According to Form’s Head of Nutrition, Dr. Adam Collins, the spot reduction myth is just that: a myth. “You can strengthen and grow muscle in a specific area, but you can’t choose where your body burns fat,” he explains. “Your body decides that, based on factors far beyond your control.”

In this article, Dr. Adam debunks the science behind spot reduction, outlines what does work for fat loss, and shares strategies to help you reach your goals without falling for fitness fads.

Why Spot Reduction Is So Appealing

From ab workouts promising a six-pack in six weeks to arm-toning routines for “Pilates arms”, fitness culture is filled with misleading claims. Many of these ideas are amplified by viral trends, influencer content, and algorithm-driven workout advice.

The truth? “There’s no shortcut to fat loss in a specific body part,” says Dr. Adam. “It’s a physiological process governed by your hormones, genetics, and overall energy balance.”

What Determines Where You Store Fat?

We all store body fat, but the where and how much is not random. It’s largely influenced by four key factors: gender, hormones, age, and genetics.

1. Gender

Women naturally carry more body fat than men, around 25 to 30 percent versus 15 to 20 percent, to support pregnancy and breastfeeding. But fat distribution also differs: men tend to store fat around the abdomen (apple-shaped or android pattern), while women store more in the hips, thighs, and buttocks (pear-shaped or gynoid pattern).

Women typically distribute fat more evenly across the body. In contrast, men often accumulate excess fat in a more centralised pattern, particularly around the waist and abdominal area.

2. Hormones

Hormones play a central role in how fat is stored and distributed. Oestrogen is a major factor in the gynoid fat pattern seen in women. It encourages fat storage in the lower body and helps regulate energy balance.

In men, androgens like testosterone contribute to abdominal fat storage. Another key hormone is cortisol, a stress hormone released via activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. Cortisol, particularly when chronically elevated, is linked to fat accumulation in the upper body and around the waist. Combined with higher testosterone levels, this can lead to increased visceral fat, the fat stored deep around internal organs. This type of fat is especially harmful and has strong links to metabolic and cardiovascular risk.

Insulin also influences fat storage. When combined with elevated cortisol levels, common in high-stress lifestyles, it can promote fat retention in central regions.

3. Age

As we age, fat levels tend to increase due to gradual declines in energy expenditure, changes in hormone levels, and shifts in lifestyle. In women, menopause plays a significant role. The drop in oestrogen not only increases the likelihood of weight gain but also shifts fat distribution toward the abdomen, a pattern more commonly seen in men.

“This creates a more male-pattern fat distribution and levels the playing field when it comes to health risks,” says Dr. Adam.

Men also experience hormonal changes with age, such as reduced testosterone, which contributes to further fat accumulation around the waist. In both sexes, ageing increases the risk of storing visceral fat, the type associated with higher long-term health risks.

4. Genetics

Your genes play a significant role in determining where and how you store fat. Research suggests that genetics may account for approximately 60 percent of the variation in fat distribution between individuals. [1]

Genome-wide association studies (GWAS) have identified numerous genetic loci linked to specific fat storage patterns. [2] These findings help explain why fat distribution varies so much between individuals, even when body weight is similar.

Ethnic background further influences fat storage. For example, South Asian populations typically have lower levels of subcutaneous fat (the type found just under the skin) and a greater tendency to store visceral fat, the deeper, more metabolically active fat linked to increased health risks. [3] Conversely, individuals of African or Caribbean descent may have different fat distribution profiles despite having similar overall fat levels. [4]

All of this reinforces the point that fat storage is not solely dictated by diet or lifestyle. Your genetic blueprint and ancestry play a meaningful role in shaping your body’s fat patterns and associated health risks.

How Fat Loss Actually Works

Losing body fat, regardless of whether it’s around your waist, thighs, or arms, requires your body to enter a state known as net lipolysis. This means your fat cells are breaking down more fat than they’re storing.

“Your fat cells are constantly shifting between storing and releasing fat,” explains Dr. Adam. “To lose fat, you need to tip the balance toward breakdown, and that only happens with a consistent calorie deficit.”

A calorie deficit occurs when you consume fewer calories than you burn. Initially, your body may draw on stored glycogen or muscle energy, but after a few hours of sustained deficit, it turns to fat reserves for fuel. This is how meaningful fat loss happens over time.

“Whether you cut calories through diet, increase your physical activity, or combine both, the deficit is non-negotiable,” says Dr. Adam. “It’s the foundation of any successful fat loss strategy.”

Not All Weight Loss Is Equal

In the early stages of weight loss, your body sheds water and glycogen, but around 50 percent of the weight lost is fat. As the calorie deficit continues, that percentage typically increases to 70 to 80 percent.

Importantly, visceral fat, the fat stored around your organs, is often the first to go. Even before you see visible changes, fat inside organs such as the liver begins to shrink. A modest 5 percent reduction in body weight can improve blood sugar control, reduce triglycerides and cholesterol, and lower cardiovascular risk.

“Fat around the abdomen often decreases before fat from the arms or legs,” adds Dr. Adam. “The so-called ‘stubborn’ fat is usually subcutaneous and slower to shift, but it’s also less harmful.”

What About Low-Carb and High-Protein Diets?

You might have heard that low-carb diets accelerate fat loss by reducing insulin and forcing your body to burn fat. While there’s some logic to this, since insulin does promote fat storage, research shows that when calories are controlled, low-carb diets do not outperform low-fat diets in terms of body fat loss. In fact, low-fat diets may even prove to be more effective in certain cases.

“People often lose more weight on low-carb diets simply because they eat fewer calories without realising it,” says Dr. Adam. “But it’s still the calorie deficit doing the work, not the absence of carbs.”

High-protein diets are often recommended during fat loss phases, and for good reason. Protein helps preserve lean muscle mass and increases satiety, which can make it easier to stick to a reduced-calorie diet. However, it’s not a shortcut.

“Protein is helpful, especially when paired with resistance training,” says Dr. Adam. “It supports muscle retention, but it won’t make you lose more fat unless you’re still in a deficit.”

Learn more about how much protein you should be eating.

Can You Target Fat Loss in Specific Areas?

The idea that you can burn fat from a specific body part, like doing crunches to lose belly fat, is one of the most persistent myths in fitness.

“You can strengthen muscles in a specific area, but that won’t necessarily reduce the fat covering them,” says Dr. Adam. “Everyone has a six-pack. You just need to lose the fat covering it to see it.”

Some studies have explored whether exercising a specific muscle group can lead to regional fat loss. These typically involve targeted resistance exercises followed by cardio to burn off released fat. But the evidence is weak and results are inconsistent.

“The studies that exist tend to be small and not particularly rigorous,” says Dr. Adam. “You might see improved tone or strength, but the fat loss still happens on a whole-body level.”

The Shivering Theory: A Glimpse Into Future Research

Some emerging research on shivering and cold exposure offers intriguing insights. Shivering stimulates the release of myokines, proteins from muscle, that signal fat cells to burn energy, a process known as non-shivering thermogenesis. This turns white fat into more metabolically active brown or beige fat.

“Shivering releases proteins called myokines, which signal fat cells to start burning fat for heat,” explains Dr. Adam. “Interestingly, some of the same myokines are also released during exercise.”

Because your body needs to dissipate heat during endurance workouts, fat breakdown may occur more readily near active muscle groups. While not true spot reduction, this mechanism might explain why fat loss sometimes appears more pronounced in areas being trained.

Smarter Toning Strategies That Actually Work

While spot reduction is a myth, you can absolutely work toward a leaner, more defined physique by focusing on overall fat loss and muscle retention. Dr. Adam recommends:

• Create a calorie deficit through a combination of diet and exercise
• Prioritise protein to preserve lean muscle
• Incorporate resistance training to build shape and strength
• Use cardio or endurance training to support fat burning
• Try time-restricted eating or reduce snacking to improve fat mobilisation
• Be patient: “The fat you care about most often takes the longest to shift,” says Dr. Adam, “but it will go.”
• Avoid drastic solutions like liposuction, which may alter appearance but not metabolic health

Final Word from Dr. Adam

Not all fat is created equal. Visceral fat is the most metabolically harmful, but also the most responsive to lifestyle changes. Fat on the hips and thighs? It’s slower to shift, but often protective, especially for women.

“No supplement or shortcut can override your body’s basic energy balance,” says Dr. Adam. “Fat loss happens when your body draws from its energy reserves to meet a shortfall. That means burning stored fat.”

“Instead of chasing quick fixes or spot-reduction myths,” he adds, “focus on sustainable habits. Be consistent, train smart, eat well, and give it time. Your body will lose fat where it needs to most, and it will thank you for it.”

So the next time you come across a fat-burning tea or 10-day toning challenge, remember, science says otherwise.

Read more: NHS – Why visceral fat matters

References

1. Pulit, S.L. et al. (2019). Meta-analysis of genome-wide association studies for body fat distribution in 694,649 individuals of European ancestry. Nature Genetics, 51(9), 1225–1233.
2. Shungin, D. et al. (2015). New genetic loci link adipose and insulin biology to body fat distribution. Nature, 518(7538), 187–196.
3. Kirk, A. et al. (2022). Ethnic differences in body fat distribution and liver fat between South Asians and white Europeans. Diabetologia, 65, 157–167.
4. Speakman, J.R. et al. (2021). GWAS for body fat distribution: Lessons from ethnicity and evolution. Genes, 12(6), 841. 

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Some people take them to support an active lifestyle or training regimen. Others turn to them in the hope of optimising their intake beyond the minimum requirements. But how many people actually take a multivitamin because of a diagnosed deficiency?

It raises an important question: Do most of us truly need a daily multivitamin, or are we just hedging our bets? According to Dr. Adam Collins, Form’s Head of Nutrition, the answer isn’t black and white.

“It’s not about whether multivitamins are inherently good or bad.” explains Dr. Adam. “It’s about who you are, what your lifestyle looks like, and what your diet is providing or lacking.”

Let’s break it down.

Can You Really Get All the Nutrients You Need from Food?

In theory, yes. A well-balanced, varied diet can provide all the essential vitamins and minerals we need. But in practice, it’s more complex.

“Not all nutrients are easily available in all foods,” says Dr. Adam. “Some, like vitamin D and iodine, are found in limited dietary sources. If those foods aren’t part of your regular intake, there’s a risk of falling short.”

Take vitamin D, for example. While our bodies can synthesise it from sunlight, this only occurs during certain months in the UK, typically between April and September, when UVB rays are strong enough. During the darker months, dietary sources like oily fish, eggs, and fortified foods become more important. Yet, data consistently shows that vitamin D intakes in the UK are often too low [1].

Iodine is another concern. Found mainly in dairy, seafood, and seaweed, it’s often lacking in modern diets, particularly those that limit animal products. The same goes for selenium and iron, depending on dietary patterns.

What About Plant-Based Diets?

Multivitamin needs become even more relevant for those on vegetarian or vegan diets. “Vitamin B12 is a textbook example,” says Dr. Adam. “You simply can’t get enough B12 from a plant-based diet without fortified foods or supplements.”

Plant-based milks and cereals are commonly fortified with B12 and iodine, which helps. But relying solely on fortification doesn’t always guarantee adequacy.

Even the EAT-Lancet planetary health diet, praised for its sustainability, may present challenges in meeting micronutrient needs [2]. With the reduction of animal products, risks of low intake for nutrients like iron, zinc, calcium, and omega-3 fatty acids increase. This makes supplementation more relevant.

What About the “Average” Diet?

Even those who aren’t plant-based may benefit from a daily multivitamin, especially if their diet is lacking in variety or whole foods.

This is where the concept of “hidden hunger” comes in. Despite overconsumption of calories, many people still fail to meet their micronutrient needs. This paradox – overnourished but undernourished – is widespread, and it’s not always obvious.

“You can be eating plenty of food but still fall short on key nutrients,” Dr. Adam explains. “In these cases, a multivitamin isn’t a cure-all, but it can help cover the gaps while you work on improving your diet.”

When Is a Daily Multivitamin Especially Helpful?

While a food-first approach is always the goal, Dr. Adam highlights several scenarios where a daily multivitamin or targeted supplementation makes particular sense:

• Pregnancy and preconception: Folic acid is essential, and excess vitamin A (as retinol) should be avoided.
• Calorie-restricted diets: Lower food intake means reduced nutrient intake.
• Weight loss medications (e.g. GLP-1 agonists like Wegovy or Mounjaro): Appetite suppression can reduce food variety.
• High training loads: Athletes may have higher micronutrient demands that aren’t always met through food alone.
• Busy lifestyles: Those who struggle to consistently eat nutrient-dense meals may benefit from baseline coverage.

“It’s not about replacing a healthy diet,” Dr. Adam concludes. “It’s about recognising when your diet isn’t doing all the heavy lifting, and when a little support from a multivitamin might help.”

So, Should You Take a Daily Multivitamin?

If your diet is consistently diverse, rich in whole foods, and well-planned – especially if you’re not avoiding any major food groups, then a daily multivitamin might be unnecessary. But for many people, life isn’t that tidy. Work, travel, stress, restrictive diets, or personal preferences can all interfere with nutritional adequacy.

That’s why we created Multi, Form’s high-quality, plant-based daily multivitamin supplement. It’s carefully formulated with bioavailable forms of essential nutrients, including vitamin D, B12, iodine, and zinc. It supports your body where your diet might not.

“The goal is to complement your lifestyle, not complicate it,” says Dr. Adam. “Multi is about giving people peace of mind, nutritional support that’s as smart and intentional as the rest of your routine.”

References

• Public Health England. Vitamin D: advice on supplements for at risk groups. GOV.UK, 2016.
• Willett, W. et al. (2019). Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. The Lancet, 393(10170), 447–492.

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Recently, you may have seen a growing number of social media posts waxing lyrical about the potential benefits of intermittent fasting, with some people claiming that it can help to reduce menopausal weight gain, as well as minimise the onset of tricky vascular issues like hot flashes. The buzz surrounding this popular eating plan has gained momentum in recent months, racking up a mammoth 5.2 million Instagram posts under the popular hashtag #intermittentfasting.

But like many things related to women’s health, the relationship between menopause and fasting is not straightforward. To help clear up matters, we asked Form’s resident health advisor, Dr. Adam, to tell us more about intermittent fasting, its safety, and its potential benefits for women during midlife.

First up, what exactly is intermittent fasting?

Intermittent fasting is a dieting approach that emphasises when you eat, rather than what you eat. The plan consists of timed ‘eating windows’ – when you can eat your usual diet – and fasting periods, when you’re encouraged to abstain from food entirely, aside from water, coffee, and tea.

The general gist is that by abstaining from grazing outside of these strict time windows, we can expand the amount of time our bodies experience being in a fasted state. Some fairly recent research indicates that the human body may experience a laundry list of health benefits from resting the digestive system, as the process is said to increase cellular repair throughout the body.

The length of each fasting window depends on the specific schedule you follow. For example, the popular ‘16:8’ method involves 16 hours of fasting sandwiched between 8 hours of eating, although some people opt to restrict their eating for longer or shorter durations.

What are the benefits of intermittent fasting during or after menopause?

Although there haven’t been specific studies on fasting during menopause, Dr. Adam says that there is some limited research into how it affects women at earlier and later stages.

“Interestingly, these research studies found that fasting can help women lose weight and improve their metabolism, both before and after menopause,” he notes. “The researchers also found that fasting eating patterns are generally easier for people to stick with than regular diets, leading to a higher likelihood of long-term sustainable results.”

Dr. Adam adds that while the benefits of intermittent fasting are generally discussed in a perimenopausal context, but strategically planning your mealtimes may actually be more helpful after menopause. “This is because of the increased weight gain, insulin resistance, and cardiometabolic risk that is more prevalent during this stage of menopause,” notes Dr. Adam.

But that’s not to say it should be overlooked in perimenopause, as the benefits of fasting seem to have ripple effects elsewhere. “A general reduction of visceral body fat tends to improve vascular function, as well as metabolic markers like glucose and cholesterol, which has been found to reduce menopausal symptoms like hot flashes,” says Dr. Adam. “Whether it’s through time-restricted feeding or alternate-day fasting plans like the 5:2 diet, fasting has been scientifically shown to improve these health markers.”

Are there any drawbacks to intermittent fasting during perimenopause?

It’s difficult to say. Dr. Adam says that it’s challenging to answer this question because there are no published studies that have specifically looked at how fasting affects women during the menopausal transition. “Key hormonal changes during this period, such as shifts in testosterone, estrogen, and progesterone, as well as regulators like sex hormone-binding globulin (SHBG) and dehydroepiandrosterone (DHEA), are all important to consider in a peer-reviewed context,” he notes.

That said, Dr. Adam believes there is little evidence that fasting has a negative effect on these hormones, apart from a slight decrease in DHEA levels before and after menopause. “Lower DHEA levels are linked to symptoms like dry skin, vaginal dryness, and reduced sex drive, but these changes are usually minor,” he assures, “and DHEA levels generally stay within normal ranges without clinical issues.” Interestingly, studies also conclude that hormone replacement therapy (HRT) doesn’t seem to impact weight loss or gain.

Added to this, an accelerated rate of bone loss, which can lead to bigger issues like osteoporosis, is a key health concern during the perimenopause. “Some people on social media argue that fasting could worsen bone loss, but there’s no evidence supporting this theory,” stresses Dr. Adam. “In fact, intermittent fasting seems to be better for bone health than traditional calorie-restricted diets, which might limit calcium intake.”

So is intermittent fasting safe and should you do it?

Overall, Dr. Adam says there’s no strong evidence to suggest that fasting poses risks during menopause, or that one type of fasting (like only eating during certain hours versus the popular 5:2 diet) is better than another.

“The benefits of fasting, such as weight loss and improved metabolism, seem to apply equally well to women during menopause,” he concludes. “However, more studies are needed to fully understand how fasting affects women during this transitional period.”

While intermittent fasting can be an approachable way to stay within a healthy weight range, it might not be right for everyone – particularly if you are taking regular medication or have type 1 diabetes. As with any major health change, it’s always a good idea to run a new eating plan past your GP first, who can help you to weigh up the personal risks and benefits.

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Thanks to the rise of fitness influencers on TikTok, fasted cardio has become a big trend amongst gym-goers; the term has racked up an impressive 55 million views on the platform, after all.

But what exactly is fasted cardio, how does it work, and if your ultimate fitness goal is weight loss, should you be doing it?

Fasted cardio explained

Fasted cardio involves doing cardio exercise on an empty stomach, typically in the morning before eating breakfast. Many people believe it enhances fat burning, but the reality is a bit more nuanced.

The idea behind it is that when you exercise without eating first, your body relies more on stored fat for energy, potentially helping with fat loss.

Does fasted cardio work?

Yes and no. While there are metabolic adaptations associated with ‘training low’ that can improve endurance and increase fat burning, these benefits are more pronounced during low to moderate-intensity cardio exercises. However, it’s important to note that the fat-burning effect of exercise extends beyond the workout itself.

A significant portion of fat burning occurs during the recovery phase after exercise, known as the EPOC effect (excessive post-exercise oxygen consumption). This phenomenon causes your body to continue burning fat to replenish energy stores depleted during exercise, particularly after high-intensity workouts like resistance training.

So, while fasted cardio can enhance the benefits of cardio-based training, it’s essential to remember that other forms of physical activity and exercise also contribute to fat burning. Plus, achieving fat loss ultimately depends on maintaining a calorie or fuel deficit, meaning you consume fewer calories or fuel than you expend.

In this context, it’s crucial to pay attention not only to your exercise routine but also to your overall diet and fueling habits. Overfueling, even if you exercise regularly, can impede your progress toward fat loss. Remember, being mindful of your calorie intake and fueling appropriately is key to achieving your fitness goals – particularly those of weight loss.

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Lack of sleep doesn’t just leave you feeling cranky and reaching for the office coffee machine throughout the day, chronic sleep issues can also increase your risk of certain health issues like depression, anxiety and hypertension.

But what effect does it have on your workout gains? If you’re religiously sticking to your early-morning gym schedule, but you’re spending night after night staring at the ceiling, will it hinder muscle growth, recovery and performance? Let’s explore.

Why sleep matters… but diet does too

When you sleep, your body goes into a mode where it repairs and rebuilds itself, including your muscles. This is what’s otherwise known as ‘rest and repair’.

But for this repair to happen effectively, your body needs the biological process of protein synthesis to take place, which is basically the process of building new proteins in your muscles. This synthesis is triggered by both exercise and having enough amino acids (the building blocks of protein) and energy from your diet in your system.

So, if you’ve worked out during the day and eaten a good high-protein meal afterwards, your body is primed to build and repair muscles while you sleep. But if you’re lacking sleep, or you’ve skipped dinner, your body might not be able to do this properly.

The effects of poor sleep

Poor sleep is associated with a higher risk of muscle injury and overtraining effects due to increased release of cytokines, similar to the body’s inflammatory response, as a consequence of inadequate sleep.

Also, when you don’t get enough sleep, your hormone levels can become unbalanced. You might have lower levels of growth hormone and testosterone, which are important for muscle repair, and higher levels of cortisol, which can interfere with muscle recovery.

Exercise can hinder sleep too

Another thing to consider is that if your muscles are sore from overdoing it during exercise, that can also affect your sleep quality. So, if you’re feeling achy after a workout, it might be harder for you to get a good night’s sleep.

There is evidence to suggest that certain foods or drinks, like tart cherry juice, might help reduce muscle soreness and improve sleep after exercise, so you might want to try stocking up your fridge ahead of your next gym session.

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Some people swear by hitting the gym first-thing in the morning, on an empty stomach, while others prefer to get a sweat on after they’ve eaten an energy-boosting breakfast.

When it comes to understanding both your blood sugar levels and the way your body burns fat, it can be tricky to know which option is better. Let’s take a look into the science, so you can make an informed decision ahead of your next workout.

First up, let’s focus on fat loss

When it comes to fat loss, we need to understand how exercise affects our metabolism. Exercise triggers a response similar to our fight or flight instinct, releasing hormones like adrenaline to provide fuel for energy. This includes mobilising fat from our fat stores to be burned during exercise.

Exercise also puts stress on our muscles, which prompts them to adapt and become better at using fuel, both glucose and fat, in the future. This adaptation involves improvements in blood supply, cellular function, and the creation of more mitochondria, the energy powerhouses of our cells. Ultimately, this enhances our ability to burn both glucose and fat during exercise.

These metabolic effects of exercise can be influenced by how you eat around your workout. The concept of “training low” involves exercising in a fasted state, with depleted glycogen stores, or without consuming carbohydrates, which are the primary fuel for exercise. The idea behind this approach is to increase the metabolic stress of exercise, triggering favorable adaptations in the body.

In contrast, supplying fuel, especially carbohydrates, can dampen this response. This leads to the logic that exercising before meals may be better for fat burning. However, it’s important to consider differences between men and women in this context. Men tend to burn carbohydrates more efficiently during exercise, while women are better at burning fat.

Unlike men, women don’t switch to burning fat as aggressively after exercise to replenish spent carbs. For women, consuming carbohydrates after exercise may blunt fat burning. This finding is consistent with studies on exercise and fat oxidation. Therefore, women may benefit from eating before exercise rather than after, or at least waiting an hour or so before consuming carbs after exercise.

What about blood sugar control?

Regarding blood sugar control, a similar strategy can be applied. Regular exercise, whether before or after meals, helps regulate blood sugar levels generally in non-diabetic people.

There is some suggestion that exercise ‘snacking’ (small bursts of activity) before meals can help minimise blood sugar spikes, and generally improve clearance of both fat and carbohydrates in the body. But exercise doesn’t need to be so regimented around meals.

I would argue that exercise, or simply being physically active, is critical to ensuring you have a turnover in your body’s carbohydrate stores, also known as glycogen, which in turn supports healthy blood sugar and fat levels.

Put simply, whether you exercise before or after meals, the key is to stay physically active consistently to support both fat loss and blood sugar control.

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The suggestion that men and women are not the same is not necessarily new and shouldn’t come as a surprise. Nevertheless, it is helpful to take this opportunity to explore how men and women differ, particularly concerning how they respond to diet and exercise.

Body Fat Differences Are Important

The first thing to note is that women have proportionally more body fat than men. As a percentage of body weight, healthy women typically have 20-30 percent body fat versus 10-20 percent in males. Moreover, women store body fat differently from men. Women preferentially store fat in subcutaneous adipose tissue, particularly around the gluteo-femoral region (hips, thighs and buttocks). Men, however, typically store fat more centrally in the abdominal area, both subcutaneously and viscerally (i.e. around the organs).

These distinctions are particularly pronounced during periods of weight gain and are partly down to hormonal differences. These are not just sex hormone differences (e.g. oestrogen) but also differing glucocorticoid release (i.e. cortisol). Because of menopause, however, preference toward peripheral fat storage becomes less pronounced, leading to more body fat centralisation.

Yet, you need to look beyond just the amount and location of body fat and appreciate how this body fat operates. Subcutaneous fat, particularly in the gluteo-femoral region, acts as a very effective “metabolic sink” for storing surplus lipid (and indirectly glucose) without issue. The turnover and release of fatty acids from this subcutaneous fat “sink” also serve as a fuel supply to other tissues like muscle. By design, this helps women fuel the energy needs of pregnancy and lactation.

Moreover, given the higher overall body fat and bigger subcutaneous fat stores, women generally have higher circulating levels of fatty acids and are better fat oxidisers than men.

It’s also one reason why, despite higher body fat, pre-menopausal women of normal body weight have a relatively lower metabolic risk than men.

Differences In Response To Exercise

Exercise is obviously associated with increased energy demand, but how we fuel the muscle to do the work is particularly important. The energy demand, and therefore the fuel mix used, depends on the exercise’s intensity. At relatively low intensity, a mixture of carbohydrates and fatty acids are oxidised to meet the demand. Still, much of the energy must come from carbohydrates at a higher intensity, along with other faster energy systems.

However, at any given exercise intensity, there is good evidence to suggest that women are better fat burners than men. There are a couple of reasons for this, one of which is the body fat differences between men and women that we have just discussed. Hormonal differences also play a role, not just androgens like testosterone, but because men release more catecholamines (e.g. adrenalin) as a consequence of exercise.

This more prominent “fight or flight response” drives greater carbohydrate utilisation during exercise. Yet simultaneously releasing more fatty acids from mainly central body fat stores, especially visceral adipose tissue, makes the body more sensitive to these catecholamines. It is incredibly relevant when it comes to post-exercise, where there is a pronounced switch to fat-burning (see my explainer on the ‘afterburn affect’, or EPOC, for more on this).

This switch to burning fat after exercise is more exaggerated in men than women, even at relatively modest exercise intensities. At the same time, in this post-exercise period, men are primed to take up any glucose and replenish their spent carb stores. Overall, men are more prominent carb burners and are better at sparing and replenishing carbohydrates post-exercise.

In contrast, women are less aggressive carbohydrate burners during exercise and generally better fat burners. Consequently, the switch to fat-burning after exercise is not as pronounced in women, particularly at low to moderate exercise intensities. In short, the fuel utilisation and exercise EPOC effect differ between men and women.

Given all the above, it is logical that the interplay between diet, meal timing and exercise may be gender-dependent. Although we have mainly looked at endurance-type exercise effects, for resistance exercise the anabolic drivers of muscle repair and protein synthesis are generally more evident in men than women. However, knowing the differences in fuelling can give some insight into how women and men can achieve the same benefits.

How Timing And Feeding With Exercise Differ

Appreciation of this systematic difference in exercise response will likely translate into different strategies for men versus women. Regarding feeding around exercise, one goal for endurance exercise is to maximise the adaptation to exercise through enhancing the cell signalling in the muscle. The recent advent of” training low” is very much in keeping with this, exercising either fasted or glycogen depleted to amplify the cell signalling effect.

However, much of this work is done in males and fits the logic that as carb burners, refraining from feeding carbs before exercise can have a significant effect. However, this may not necessarily hold for females. In contrast to males, we have observed in several studies that the blunting effect of feeding carbs is actually in the post-exercise period rather than pre-exercise.

Mainly as this dampens the more subtle switch to fat-burning and can serve as a carbohydrate overload, males may benefit from training low, but females may be better off recovering low. That’s not to say women must eat before, nor that women can’t have anything post-exercise, especially as we have seen that protein does not have a blunting effect, it is just the feeding of carbohydrate afterwards that has an impact.

Relating this to the recent study mentioned in the intro, on the optimum time of day to exercise, the researchers noted that women in both the AM and PM groups didn’t change their fat oxidation, unlike the men, partly explained by the fact that all exercises (AM and PM) were performed “fasted”. In addition, meals for all participants, both male and female, were eaten post-exercise.

Nevertheless, both female exercise groups still lost body fat, with the AM group losing more, possibly because breakfast was a smaller meal and less blunting than dinner. In contrast, males seemed to benefit more regarding resting fat burning, with the PM group having a more significant increase. Such an observation is in keeping with the “train low” model. It could also be because the PM group will likely continue this elevated fat oxidation to the following day when the resting measurements were taken.

Fuel availability is one of the critical anabolic drivers of muscle repair and protein synthesis, mainly feeding carbohydrate and amino acids, like leucine. So nutrition post-exercise in both men and women is helpful for these anabolic adaptations to the muscle. But what about resistance exercise? The observation that strength gains were more pronounced after PM exercise may be down to generally better exercise performance at that time of the day (i.e. more work achieved). However, it could also be because the post-exercise meal may be more substantial (e.g. in terms of protein and carbohydrate).

So, in summary, knowing the physiological differences can help tailor your exercise and your diet for maximal gain — a simple way of achieving a level of personalised nutrition.

Further reading

Shamlan G, Bech P, Robertson MD, Collins AL. Acute effects of exercise intensity on subsequent substrate utilisation, appetite, and energy balance in men and women. Appl Physiol Nutr Metab. 2017 Dec;42(12):1247-1253. DOI: 10.1139/apnm-2017-0280. Epub 2017 Aug 1. Erratum in: Appl Physiol Nutr Metab. 2020 Aug;45(8):915. PMID: 28763620

Fuchs, A., Young, H., Booth, H., Armitage, F., & Collins, A. (2011). Investigation into gender differences in the effects of feeding around exercise on energy expenditure and substrate utilisation. Proceedings of the Nutrition Society, 70(OCE6), E380. doi:10.1017/S0029665111004654

Honnor, M., Herdsman, M., & Collins, A. (2012). The effect of food timing on fat oxidation during exercise and resting recovery. Proceedings of the Nutrition Society, 71(OCE3), E236. doi:10.1017/S0029665112003278

Morencos, C., Scott, G., & Collins, A. (2017). Investigation into the influence of food timing around exercise training and the effects on energy and metabolic health: Is it better to eat before or after exercise? Proceedings of the Nutrition Society, 76(OCE2), E36. doi:10.1017/S0029665117000921

The post Ask Dr Adam: How Do Women Need to Train Differently From Men, and Vice Versa? appeared first on Form.

Firstly, calories are an established, quantifiable and clearly defined unit of energy, like any other designated unit, whether that be volts, kg, metres, or minutes. They do not change. A meal of 800kcal will still be 800kcal, irrespective of where those 800kcal are coming from (i.e. carbohydrate, fat, protein, fibre and alcohol). Not all dietary components generate the same diet-induced thermogenesis and net metabolisable energy. But, after factoring in these variations in diet-induced thermogenesis, the consumed 800kcal is all accountable in terms of energy balance. Hence, we do not just magically lose or gain calories.

Sadly, the truth is complicated and often oversimplified or misunderstood by many. Nevertheless, questioning whether a calorie is a calorie is helpful as it implies that the fate of the consumed calories is different depending on where these calories come from, which is technically accurate.

To better understand and contextualise what this means, we must look beyond just “calories in and calories out” and even beyond energy homeostasis, and fully appreciate energy metabolism which is crucial if wanting to predict the likely metabolic fate of the fat, protein, carbohydrate, and alcohol consumed. Indeed, such knowledge and understanding are fundamental to all of nutrition science and its application (health, disease, weight management, exercise science and beyond).

Beyond Energy Balance

We do not get our energy (calories) by plugging ourselves into the mains, but by burning the “fuel” that we have assimilated from food and drink. These fuels are our macronutrients (carbohydrate, fat, protein) and alcohol. Indeed, we know that our calculated energy intake hinges on knowing how much (e.g. in grams per day) of our “fuels” we are consuming and converting this into energy (calorie) equivalents. But rather than doing this, we can just consider the absolute amounts of carbohydrate, fat, protein and alcohol consumed, as this reflects our fuel (substrate) intake or, from a metabolic perspective, our intake of energy substrates.

On the other side of the energy balance equation, we consider how much energy we are expending like taking meter readings at home to calculate our energy bill. But instead, we can alternatively look at what fuels we are actually “burning” to provide this energy i.e. how much of our energy substrates carbohydrate, fat, protein and alcohol, have we burnt.

Combined, this fuel’s view of energy balance overall compares “fuels consumed versus fuels oxidised (burnt)”. Furthermore, you can view this on a fuel-by-fuel basis i.e. carbohydrate intake versus carbohydrate oxidation, fat intake versus fat oxidation, protein intake versus protein oxidation, and alcohol intake versus alcohol oxidation. Helpfully, we can measure substrate oxidation, as well as substrate intake.

Indirect calorimetry can assess oxygen consumption and CO2 production, and from this, we can calculate the respiratory exchange ratio (RER), which simply divides CO2 produced by O2 consumed. This ratio is also commonly termed your respiratory quotient (RQ), but this assumes that what you are measuring through breath reflects what is going in your tissues. Significantly, your measured RER (or RQ) will differ depending on what fuel you are oxidising.

We typically oxidise a mixture of fuels simultaneously, but the RER (or RQ) value indicates what fuel you are predominantly oxidising. Amino acids are typically not directly used as an energy substrate, so we often assume a fixed or constant protein contribution to the fuel mix or look at the non-protein RQ. Unless we are burning alcohol, the variability in the fuel mix is between fat and carbohydrate. An RQ (or RER) closer to 1.0 indicates carbohydrate oxidation predominantly, whereas closer to 0.7 implies more fat oxidation.

More usefully, we can use this tool to determine how our fuel mix changes, for example, after feeding or exercise. For example, feeding carbohydrate will typically shift you towards more glucose oxidation. With the help of metabolic chambers, we can also assess how 24-hour substrate oxidation rates may match up to the fuels consumed.

The Problem With Fat Balance

Let us now examine fuel balance over a typical 24-hour period for a typical healthy adult. We shall compare intake versus oxidation (or expenditure) for each substrate (carbohydrate, alcohol, protein and fat), and we shall compare intake versus oxidation (or expenditure), as depicted in the chart below.

So, when considering alcohol, metabolically, all alcohol (ethanol) consumed will be oxidised within 24 hours; we do not have ethanol stores in the body. Hence there is always a perfect balance between alcohol intake and alcohol oxidation. When we consider protein, we also know that, unless someone is undertaking growth or has infection or trauma, amino acid intake is near perfectly matched with amino acid oxidation. Indeed, this is the whole premise behind protein (nitrogen) balance, where nitrogen intake (mainly from protein) equals nitrogen excretion (urea and ammonium ions in the urine).

Carbohydrate intake will also lead to increased carbohydrate utilisation, predominantly through the action of insulin to maintain glucose homoeostasis. This regulation means, over a typical 24-hour period, carbohydrate intake is equal to carbohydrate oxidation. Overall utilisation and oxidation of alcohol, protein and carbohydrate are regulated to match their availability/supply. That is not the case for fat though.

Fat oxidation is influenced and controlled by the availability of other substrates, mainly carbohydrate and alcohol, not fat intake itself. Unlike the other energy substrates, there is no regulated balance between fat intake and fat oxidation. Fat oxidation will mainly occur in the absence of carbohydrate. Similarly, surplus carbohydrate may lead to net storage of fat and possibly increased fat synthesis (i.e. more available fat as a fuel).

Viewing energy balance in terms of substrate balance then helps us understand more about the operational consequences of any energy imbalance. It suggests any overall energy (calorie) imbalance will likely manifest as a change in fat balance, explaining why, certainly in the medium to long term, shifts in energy balance result in significant changes in body fat.

This is an edited excerpt from Dr. Adam Collins’ upcoming book the Metabolic Manual. To read more articles by Dr Adam click here.

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However, viewed from a different perspective, these side effects of exercise are representative of the very processes that are helping the muscle to “get better” and improve you in the long run. To explain, we can look at the two main types of exercise.

Endurance Exercise

Endurance exercise, sometimes referred to as cardio or aerobic exercise, describes a moderate intensity of exercise sustained over a prolonged period. Endurance exercise requires continual energy (ATP) production in the muscle, mainly through oxidative processes in the mitochondria. However, the rate at which you can generate ATP is dependent on the respiratory chain — a series of redox reactions moving electrons from one molecule to another to end up combining with oxygen ultimately — and is reliant on a supply of oxygen.

When demand for energy production increases, some electrons will inevitably “leak” out of the respiratory chain. Given that more oxygen is in the muscle, these electrons can interact with the present oxygen and nitrogen. They are creating free radicals, specifically reactive oxygen species (ROS) and reactive nitrogen species (RNS).

These ROS and RNS are natural byproducts of mitochondrial respiration and are produced in significant amounts during exercise when energy production is high. However, levels are still within a manageable range in the muscle and will not necessarily cause damage. Instead, they act as a helpful trigger in the muscle to orchestrate cellular changes. Through mediators such as nuclear kappa beta and mitogen activating protein kinases, changes in gene transcription instruct the cell to alter manufacturing.

The goals are to trigger changes such as increased muscle fibre production, metabolic enzymes, and the creation of more mitochondria. All of which will adapt the muscle to better cope next time.

In addition, other cell signalling mechanisms are initiated in response to more free radicals and energy depletion. AMP kinase, in particular, is activated when the energy status of the cell is low. Via the cellular survival mechanism of PGC1a and SIRT1, this can further enhance mitochondrial production and better glucose uptake (increased GLUT4) and improved insulin receptor function (i.e. insulin sensitivity) in the muscle.

It may also help with the uptake and temporary storage of fat in the muscle, as an additional fuel reserve, with a greater ability to oxidise fat due to the increasing mitochondria and other metabolic adaptations — all helpful to import and utilise fuel better next time.

Resistance (+ High Intensity) Exercise

With resistance exercise, similar mechanisms to those described with endurance exercise will also occur, and also in higher intensity exercise to some extent. However, resistance exercise is also conducive to the physical strain on the muscle and potential damage to muscle fibres, particular when that exercise has some concentric features like unfavourable lengthening of the muscle and muscle ‘micro-tears’.

In essence, you damage the muscle fibres through the physical load or pull them apart. Such stress will trigger a traditional inflammatory response to facilitate repair, by example, increasing blood flow and fluid to the muscle — which makes your muscles look artificially more significant after a heavy workout — and releasing inflammatory cytokines.

This collective inflammatory response triggers the same cell signalling response described for endurance, with gene transcription changes altering manufacturing and an increase in importing materials and energy. In this case, the emphasis is on increasing protein synthesis of myofibrillar proteins for muscle fibre repair, rather than mitochondrial proteins in endurance exercise.

There is, therefore, a more pronounced trigger of the mTOR pathway to drive this protein synthesis. In keeping with this, the uptake of amino acids and glucose is enhanced, helped by the general inflammatory response that has already increased blood flow to the muscle.

Help Or Hindrance?

Appreciating these natural adaptation processes can help decide how best to achieve the benefits of exercise. With endurance exercise, the energy crisis created is an essential initiator of improvement. Hence, there is the suggestion that over fuelling the muscle, can potentially blunt some of the cell signalling that facilitates metabolic adaptation. In addition, free radicals are not necessarily bad guys, and levels produced do not necessarily represent oxidative stress which can be damaging.

There is some evidence to suggest that overdosing on antioxidants may also have a blunting effect, particularly in the pharmacological doses found in many supplements. This may be more apparent when the overall volume of exercise is low such as in the amateur athlete or average exerciser.

Nevertheless, there is some suggestion that more natural provision of antioxidants through diet, and certain polyphenols like curcumin for example may be of benefit. Plus, if the training volume is very high, a consideration of antioxidant supplementation may be more appropriate.

For the resistance exercisers, the muscle soreness experienced is likely a signal that your muscle is repairing, and while you should rest and refrain from straining the muscle again in the short term, this is not to say you should stop exercising altogether. However, don’t ignore the soreness; repeated damage and stress on the muscle without time to repair will ultimately lead to declines in muscle function and ultimately gains in performance.

Further reading

Hawley JA, Burke LM, Phillips SM, Spriet LL. Nutritional modulation of training-induced skeletal muscle adaptations. J Appl Physiol (1985). 2011 Mar;110(3):834-45. doi: 10.1152/japplphysiol.00949.2010. Epub 2010 Oct 28. PMID: 21030665.

Slattery K, Bentley D, Coutts AJ. The role of oxidative, inflammatory and neuroendocrinological systems during exercise stress in athletes: implications of antioxidant supplementation on physiological adaptation during intensified physical training. Sports Med. 2015 Apr;45(4):453-71. doi: 10.1007/s40279-014-0282-7. PMID: 25398224.

Merry TL, Ristow M. Do antioxidant supplements interfere with skeletal muscle adaptation to exercise training? J Physiol. 2016 Sep 15;594(18):5135-47. doi: 10.1113/JP270654. Epub 2016 Jan 18. PMID: 26638792; PMCID: PMC5023714.

Gomez-Cabrera MC, Viña J, Ji LL. Role of Redox Signaling and Inflammation in Skeletal Muscle Adaptations to Training. Antioxidants (Basel). 2016 Dec 13;5(4):48. doi: 10.3390/antiox5040048. PMID: 27983587; PMCID: PMC5187546.

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Ultimately, this device is a simplified method of indirect calorimetry using CO₂ percentage in the breath as a proxy measure for the Respiratory Exchange Ratio (RER). However, RER requires a measurement of O₂ alongside CO₂ to ascertain substrate utilisation truly.

Nevertheless, the devices have undergone some validation through comparison with traditional indirect calorimetry and actual measures of RER in a fasted state and after consuming a lot of pure glucose solution (150g).

As expected, RER increased in response to drinking the glucose, reflecting an increase in carbohydrate oxidation. CO₂  percentage measured by the device also increased, albeit the size of difference varied a lot between people. It supports the idea that simple at-home measures of CO₂ through devices like this may give insight into whether you are burning carbs.

But it is by no means an accurate measure, and how reflective or accurate this is will likely be very variable among people. We know that spot measures of RER are influenced by many different factors and down to the device’s technique. Moreover, we are not measuring just a series of individual breaths in indirect calorimetry. We typically measure many breaths over time, perhaps over several minutes, repeated over many hours or even measured continuously across a whole day.

Despite these limitations, the success of these devices is that they can serve as an educator and enforcer of behaviour. Getting people to appreciate the importance of what you are burning for calories, not just how many calories you are burning, can be helpful. Like all tracking devices, its impact is that it makes people more conscious of what they are eating and can help people follow new regimes by perhaps demonstrating the “benefit” of what they are doing.

It is a potentially powerful convincer, sold as a way that you can “hack your metabolism”. It can also help introduce people to metabolic flexibility – the ability to switch fuels, for example, in response to eating or fasting – which is an important consideration.

This is an edited excerpt from Dr. Adam Collins’ upcoming book the Metabolic Manual. To read more articles by Dr Adam click here.

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