In part 1 of this series I discussed how there are many complex factors that influence the “calories in vs calories out” equation that is used for weight loss. We looked at the various factors that influence our caloric intake on a daily basis.
When it comes to caloric output, there are more considerations beyond exersize to take into account. And just like caloric intake, the factors governing the amount of calories burned per day is quite complex. However, similarly to the factors governing caloric input, addressing the factors that govern caloric output can allow us to develop a diet and lifestyle template that addresses and utilises these factors to enhance weight loss.
Factors effecting caloric output:
1) Basal metabolic rate (BMR): BMR is the estimated amount of calories that we burn per day just to survive and keep all our organ systems ticking over. It makes up approximately 60% of our caloric output and it is related to our age, sex, weight, hormonal status (i.e. thyroid, sex hormones, leptin cortisol), gut bacteria, muscle mass and whether we are stressed, injured or sick.
While BMR does vary from person to person, it is not always as large as most people think. It is often thought that a person who is overweight has a slow metabolism (BMR), however these people in fact have a higher metabolism to upkeep their weight and moving a heavier body around requires more energy.
A “slow metabolism” is also usually blamed for weight gain and while it does differ from person to person, due to the factors above, for a given life stage (i.e. slows with age), it doesn’t vary as much as people think, which is why studies show it is not a good predictor of weight gain. The other factors effecting caloric input discussed in the last post are greater determinants of weight gain.
Furthermore, thyroid function does effect metabolism, however it is negligible in terms of its effects over weight loss when compared to caloric intake and caloric output. If thyroid function is slowed (which may be due to insulin resistance, inflammation in the body and leptin resistance from weight gain), it will cause hypothyroid symptoms and exacerbate weight gain by increasing caloric intake. However, a slow thyroid has a very negligible effect in overall caloric output.
Lastly, BMR reduces as a person loses more weight, because there is less weight to move around and sustain. This is why people need to keep lowering their caloric intake as they lose more weight.
Obviously this varies from person to person due to the type of exercise, the intensity and duration.
There is much debate in the fitness industry about the best form of exercise. However for weight loss, some form of strength and conditioning, in which a person can increase their muscle mass, appears to be the best.
This is because increasing muscle mass, increases a persons resting metabolic rate as muscle requires a lot energy to house in the body and repair after a workout.
Therefore if a person is not over consuming calories, their fat stores will be used as energy to maintain their muscle mass (as long as adequate protein is ingested to support muscle repair and growth). It is also important to make sure that strength-training regimes keep a persons heart rate elevated for extended periods of time, as simulating the cardiovascular system is also important for health.
Despite this, ultimately some exersize is better than none. As long as a person is in a caloric deficit, they will loose weight. Increasing caloric output via exersize simply helps with increasing the caloric deficit due to increased energy output.
As a person loses more weight, their caloric output during exercise becomes less, because they are moving less weight, which requires less energy. This is why the duration and intensity of exercise must increase as weight loss occurs.
3) NEAT (Non-exercise activity thermogenesis):
NEAT is also variable between people and it involves all the things we do in our day that is not exercise related but it is movement that obviously requires caloric output from the body. Implementing habits such as using a stand up desk at work, using the stairs instead of the elevator, pacing while on the phone, requiring good posture while sitting, fidgeting and parking further away from your destination can all increase your NEAT substantially and can contribute to weight loss.
As hunter gatherers we used to be less sedentary and move around a lot more in our day, this was because if we sat down all day, we would starve. We had to move around to forage food and hunt, as well as survive. We were genetically designed to move throughout the day. However, nowadays there is a mismatch between our genetic code and our environment, which contributes to disease and weight gain.
In our modern world, we lack consistent movement on a daily basis, especially because we no longer have to “fight” to survive. For example, to get food we simply can go to the supermarket or even sit on the couch and order it to our door. Also, many people work at desk jobs, drive/commute to work in a seated position, only to come home after work and continue sitting on the bed, couch or at the diner table.
This creates limited movement throughout the day and decreases the amount of energy expended throughout the day, which in turns decreases overall caloric output. This is also compounded by increased caloric intake during the day of high calorie, readily available foods. On top of this, as we get older we become even less active/mobile, we move around less and our metabolism slows, which is one reason as to why weight gain increases with age, even if our caloric intake stays the same.
Therefore, while daily exersize is important for increasing caloric output, so is daily movement throughout the day.
4) Thermic effect of food:
This relates to the amount of energy required to digest and store the food we eat. The energy output required to digest and absorb food varies between foods. There is a particularly large difference between the energy required to digest whole foods compared to processed foods.
Whole foods that are minimally processed require a lot of energy for the body to digest when compared to processed foods due to the presence of things like fibre and protein. Protein dense food require the most energy to digest and they are very satiating foods, which is why protein is a very important part of weight loss diets.
It must also be noted that it is commonly thought that eating small meals throughout the day “boosts” metabolic rate due to the thermic effect of food. However, as long as the caloric intake between two people are the same, food frequency seems to have little effect on overall calories burned throughout the day.
What does this all mean?
The weight loss industry is a billion dollar industry. Despite the amount of money poured into weight loss diets and supplements, obesity rates are still on the rise. The issue with most weight loss diets is that they fail to take into consideration the complex mechanisms and habits behind weight gain.
Most fad diets severely restrict calories via a low caloric diets, food group removal or meal replacement shakes, however they do not involve helping people to change the poor habits that lead to weight gain in the first place. If followed correctly, there is no doubt that these diets will help people lose weight very quickly because their caloric restriction is so severe. However, most people regain their lost weight (and more) after these diets because it didn’t help them change their poor habits that lead to weight gain in the first place.
Fad diets can also advocate for total elimination of food groups, which is unsustainable and lacks scientific evidence. They may advocate for a one size fits all approach to diets, which is never ideal. They also can lead to nutrient deficiencies due to low caloric intake (the body needs nutrients to function properly). Sometimes these diets can initially make people feel really good if the person is transitioning from a high calorie, low nutrient density diet.
Also fad diets can cause obsessiveness over food, social exclusion due to food restriction, as well as feelings of guilt/shame if a person strays from the diet, leading to binging, which is obviously counter productive.
Accumulation of failures on fad diets kills a person’s motivation, especially if they keep gaining more weight. What tends to happen is that people go through “all or nothing” diet phases where they make drastic and unsustainable changes. Then once they stray from their “diet,” they usually go backwards in the opposite direction.
Muscle loss can also occur due to restricting calories and not eating enough protein on these diets. Muscle is an important marker of health and it also helps to burn fat as it is metabolically expensive to hold in the body. This is why on a caloric restrictive diet, the first thing the body will do is eat at your muscle. This is a means of conserving energy.
Furthermore, as seen the the last post, fat is our body’s main energy reserve an it is regulated by our bodies set point. The set point is the preferred amount of body fat the body tries to maintain and will defend. The body fat set point increases as people gain more weight because the body prioritises weight gain. This is an evolutionary mechanism that ensured our survival as a species in times where food was scarce. However, nowadays food is readily available, which leads to this mechanism causing weight gain.
When individuals eat below their set point (i.e. caloric deficit), the body activates physiological mechanisms to try and up regulate fat storage, in order to re-establish the set point. These mechanisms are things like increased hunger cravings, lowered metabolic rate, fatigue and down regulating all “non-survival” mechanisms like reproductive health. The more severe the caloric deficit, the more overweight a person is and the longer the amount of time they have been overweight for, the stronger these mechanisms are. This demonstrates that the undesirable effects of dieting and weight loss are variable between people.
These metabolic processes in place to resist weight loss (e.g. fatigue, lowered metabolism and hunger cravings) are part of a particular evolutionary mechanism, which ensured our survival as a species. When a person eats below their set point, the body literally thinks it is starving and there is a famine, so it does all that it can to make up for the lost calories, which is why people experience fatigue and hunger cravings. The body is slowing down its metabolic rate to conserve energy until food arrives.
This evolutionary mechanism does not fit into our modern environment, because these metabolic processes are in place to help us cope with food scarcity, which is no longer an issue. This shows how our genes are at a mismatch with our current environment.
Also, if a person has been yo-yo dieting for quite sometime, these mechanisms become more intense. This s because yoyo dieting and fluctuations in weight lead to an increase in set point over time. Which is usually why people gain even more weight than they tried to initially loose after a fad diet.
The body does this as an adaptive response. As mentioned above, caloric restriction, especially drastic caloric restriction is seen as a stressor on the body and it thinks it is starving. Once the metabolic processes are put in place to replace lost calories, the body will raise the set point in order to prepare for the next time there is a “famine” or period of “food scarcity,” which is now in the form of dieting.
These factors are why people who have been dieting for years, find that the hunger cravings with dieting are unsustainable. The many failures on these diets can kill peoples confidence as well as their motivation.
As mentioned above, if these diets are followed, it will cause weight loss, however it very hard to maintain long term due to all of the metabolic processes in place to try get you to re-feed your body. In weight loss, your body is literally working against you and doing all that it can to resist the loss of more body fat.
Losing weight rapidly makes the body panic and causes these metabolic processes to go into overdrive. The set point will only change if weight loss is sustained for a long period of time, which is unlikely due to food cravings and a lack on knowledge around good diet and lifestyle habits to maintain weight loss.
Also, losing weight very quickly can actually damage a person’s metabolism, where their body takes up to 7 years to re-adjusts to a new set point. This means the adaptive mechanisms of the body in response to a lowered caloric intake (e.g. fatigue, cravings, hunger and lowered metabolic rate) persist, even when the person is at a new body weight. This makes sustained weight loss extremely difficult.,
Resetting the body’s set point takes consistent, sustainable, healthy diet and lifestyle choices that lead to gradual weight loss. The slower the weight loss, the more time the set point has to change as you go. The body doesn’t panic as much as it doesn’t think that there is a drastic “shortage” of food.
Lastly, these adaptive mechanisms also mean that a person, who has lost weight, may have to consume fewer calories than a person of the same weight that has never been overweight..
The appealability of fad diets is that we live in a world of instant gratification and quick fixes. Even the medical model functions in this way where we treat symptoms of health issues with a tablet, rather than addressing the underlying diet and lifestyle causes. Good health and weight loss takes time and consistency. It is about doing the right things, majority of the time.
Ultimately part 1 and part 2 of this blog series show the interact complexities of weight gain and weight loss. There are a multitude of factors that govern our caloric output and input. However, now that we understand this, it is easier to form sustainable diet and lifestyle strategies that can help us with weight loss, which address all the factors that govern caloric intake and output, rather than purely focussing on caloric intake – which is the main issue around fad diets as shown above. In Part 3, I will outline strategies to lose weight, which take into consideration the factors that drive weight gain.