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How Our Obsession With Calories Buried A Fitness-Oriented Approach To Weight Loss

The Problem With Calories

As a biomedical researcher and fitness enthusiast, nothing sparks my curiosity more than understanding the multitude of ways that exercise influences our health. Our very existence, the evolution of humans beings, is intricately tied in with our capacity to perform physical activity. Although to a much lesser extent in modern society, speed, strength and endurance have shaped the course of history. While we are each confined by the walls of our unique genetic limitations, we still possess a substantial level of control over our physical fitness.

I always hoped to spend part of my career studying how different types of physical activity affect cellular and physiological processes and, in turn, how these processes influence the development and prevention of lifestyle diseases. Before pursuing my doctorate degree, I remember speaking with several academic researchers about the future of the field. I quickly came to learn that I was a generation too late, that research into the benefits of exercise had already become far less lucrative. But it’s not for the reason you might think. Although we had discussed some scientifically meritable theories, the problem that I kept running into, as far as Ph.D. research projects were concerned, was that “everybody already knows that exercise is good for you.” And, as a consequence, funding studies on the benefits of exercise has seemingly becoming more difficult.

The world is starting to look elsewhere for answers because there’s simply nothing new or exciting about exercise. Although I don’t agree with the direction we are headed, it’s true, you can only get out as much as you put in to a workout. There are no hacks or shortcuts.

Most people fall into one of three categories when it comes to exercise. If you’re like me, you love working out, you feel as if you can’t function properly without it, you’re completely hooked. On the other hand, you may be someone who gets little pleasure from exercise. You do it because you know it’s good for your cardiorespiratory health, your metabolism and managing your body weight. For the most part, it’s an obligation that you don’t look forward to. Finally, you may be someone who just doesn’t exercise much. It’s not one of your priorities and working out is not a major part of your lifestyle.

Regardless of your commitment to physical activity, there are some clear observations that we can make about regular exercise and body composition. People who perform physically demanding exercise tend to be in better shape than those who don’t. And this can easily be explained by the way your body adapts to working out. Think about professional athletes. Even think about friends and colleagues who are dedicated to hitting the gym on a regular basis and play on sports teams. It’s not much of a stretch to say that the more you physically challenge your body, the more athletic your body composition. I’m not saying that exercise is the be all and end all of looking good and feeling healthy. Diet and other lifestyle choices certainly play an important role too. But there is something about high-performance exercise that cannot be replicated when striving for improvements in body composition.

Unfortunately, in the dieting industry, a single buzzword has become more powerful than all forms of scientific reasoning. When we talk about losing weight or getting into shape, we immediately think about “calories.” The word alone can make or break your day. Many people, in my view, spend far too much time tracking the calories in their food, counting their calories on the treadmill, and obsessing relentlessly over the idea of “calories in, calories out.”

Diet fads are so named because they can only offer short-term, albeit rapid, weight loss. They are fads for a reason and, sooner or later, their scientific flaws turn into practical shortcomings. This is evidenced by the fact that, under clinical settings, the vast majority of dieters end up putting back on all the weight that they lose. If the story were truly as simple as “calories in, calories out”, all you’d need to do to is stop eating entirely until you reached your desired body weight. This is precisely where our obsession with calories has led us astray. In most cases, we undertake a new diet and exercise plan either to get healthier or to look better. The ultimate endpoint, in either case, is not really about a number on the scale, but rather, a measurable improvement in body composition.

Logically, a calorie deficit can be created by either reducing the amount of food you eat (calories in) or increasing your level of physical activity (calories out). The greater the calorie deficit, the faster you will lose body weight. But your body doesn’t think in calories. Living in a prolonged state of calorie deficit usually leads to adaptive thermogenesis, a global reduction in metabolic rate. On top of this, as you lose weight through a calorie deficit, you have little control over the proportional loss of fat mass and lean mass. And this is an important consideration since lean mass is a greater contributor to your metabolic demands than fat mass.

If we think of our bodies as highly adaptable machines, in order to create sustainable long-term changes in body composition, we can’t solely focus on how much fuel we put in or how much fuel we go through. Wouldn’t it make more sense to modify the machine so that it starts to burn fuel the way we want it to?

Burning Carbohydrates & Fats: The Exercise Effect

Can exercise lead to sustainable changes in body composition? How is it any different to the revolving door of diet crazes?

Your body produces energy primarily by burning two fuel sources, carbohydrates and fats. From an evolutionary perspective, neither is inherently better or worse than the other, and you can adapt to using different proportions these fuel sources based on your diet. However, when you are performing metabolically demanding physical activity, your body follows a set of guidelines that determine how fuel sources are to be used. Clinical research has highlighted that maximal fat oxidation occurs at an exercise intensity of 45–65% of your maximal aerobic capacity (VO2 max). It is important to clarify that your VO2 max is not the upper limit of your workout intensity. Activities such as sprinting and resistance training go well beyond your maximal aerobic capacity and depend on rapid energy production that does not require the delivery of oxygen to your muscles. This type of anaerobic energy production allows us to make spontaneous and high-intensity movements. Imagine if we had to start breathing heavily before we even started to run. It certainly wouldn’t be an evolutionarily stable approach. Aerobic and anaerobic energy production work hand in hand and allow us to meet the demands of physical activity. While anaerobic means of energy production are immediate, they are also limited and exhaust rapidly. Your maximal aerobic capacity, on the other hand, defines the upper limit of how much oxygen your body can use to generate energy. Theoretically, you could continue to meet energy demands while working at your VO2 max indefinitely. However, in reality, your body would burn through its fuel sources and fatigue would set in, bringing an end to your work out.

Since the discovery of a target exercise intensity for maximal fat burning, there has been ongoing debate surrounding the best kind of physical activity for getting rid of excess fat. Much of the discussion surrounds the fact that when exercise intensity goes beyond the fat burning zone (>65% VO2 max), carbohydrates take on an increasingly important role in energy production at the expense of fat oxidation. While it’s true you can optimise fat oxidation during the course of a single workout by exercising at 45–65% of your VO2 max, there are several arguments for why this is not necessarily the best long-term strategy for improving your body composition.

Firstly, VO2 max is only a relative measure of exercise intensity. In other words, it varies from person to person and changes with your fitness level. Exercising at 50% VO2 max is drastically different between a trained runner and a sedentary individual. The runner, with a higher base level of fitness, would be performing a more intense workout than the sedentary individual and would therefore utilise more energy during their workout, burning both more carbohydrates and more fats. The point here is that in order to drive metabolic adaptations that favour fat burning, you should aim to improve your physical fitness (speed, strength and endurance). In other words, you want to become the runner. But this can only be achieved by progressively challenging your body with increasingly demanding training sessions.

Secondly, your body is better designed to store fat than it is to burn it. From an evolutionary perspective, fat stores are your body’s insurance policy. Accessing food has never been as easy as it is today. So, it makes sense that an efficient strategy for energy storage was critical throughout the course of evolution. However, there is an exception to this rule. When performing demanding physical activity, it is in your body’s best interest to burn fats, rather than carbohydrates, whenever it is possible. This phenomenon is known as carbohydrate sparing.

Generally speaking, the higher your fitness level, the greater your capacity to spare carbohydrates. But why would such a strategy have evolved given the high priority for fat storage in our bodies? Although many theories have been expressed by researchers, carbohydrate sparing is considered a means to prolonging physical activity. At all times, your body must maintain its blood sugar concentration above a critical minimum level. If blood sugar drops too low, we experience symptoms of hypoglycemia, such as dizziness, lightheadedness and fainting. The same rule applies to when we are exercising. We have to maintain a critical blood sugar level, otherwise, the symptoms of hypoglycemia will bring our workout to an end.

Today, performing physical activity to the point that you faint only occurs in fairly contrived circumstances, such as marathon running or overexertion during high-intensity sport. However, it is not so far-fetched to see how fainting during physical activity had more severe outcomes in the context of evolutionary processes. It could definitely have made the difference between escaping and being caught or surviving long-distance migration.

Metabolic Adaptations For Survival & Weight Loss

Putting exercise back into an evolutionary context empowers us to make better informed decisions about our body. So, rather than fixating on calories and working within our current metabolic limitations, why don’t we use our knowledge of exercise physiology to drive the adaptive changes in body composition that we desire?

So, what does it actually mean to improve your fitness? For me, it comes down to the same three factors that have been so critical throughout history, speed, strength and endurance. Speed and strength are primarily derived from fast-twitch muscle fibres, which can be developed using both resistance and high-intensity training methods. These types of training are performed beyond the VO2 max and result in increased muscle mass, which not only requires energy to build, but also to maintain. Endurance, on the other hand, is mainly derived from slow-twitch muscle fibres, which can be developed by exercising for prolonged periods of time slightly below the VO2 max. While these muscle fibres do not generally increase greatly in size, they are capable of greatly upregulating mitochondrial density.

Improved fitness can be viewed as the ability to perform physical activity with greater ease over time. But this ability is underpinned by adaptations to metabolically demanding exercise. Increased mitochondrial density enhances your VO2 max, which ultimately promotes carbohydrate sparing and preferential fat burning. Increased muscle mass, in the context of weight loss, enhances your total metabolic rate. These changes are the new parts of your ever-adaptable machine, which is now better equiped for burning fats and sparing carbohydrates. Although reprogramming your body may be a gradual process, it explains why exercise can actually drive sustainable changes in body composition.

And all that talk about calories? Perhaps we have greatly underestimated the body’s ability to reshape itself according to metabolic demands. The one thing that I’m sure of, however, is that there is definitely more to the story than “calories in, calories out.”


The Regulation Of Carbohydrate And Fat Metabolism During And After Exercise

Understanding the factors that affect maximal fat oxidation

Relationship between percentage of VO2max and type of physical activity in obese and non-obese adolescents

Weight Science: Evaluating the Evidence for a Paradigm Shift

Collateral fattening in body composition autoregulation: its determinants and significance for obesity predisposition