Key Assumptions – Calories Part III

By Jason Fung, MD

Key Assumptions
Click here for Calories Part I . Here’s how we conventionally think about obesity.

Conventional Theory of Obesity

Assumption#1 Calories in and calories out are independent
The first key assumption is that calories in and calories out are independent of each other. That is, if you reduce calories in, calories out are not affected. This is crucial. If a reduction of ‘calories in’ causes a reduction in ‘calories out’, then weight is not lost. It is only the “margin” or the difference between calories in and calories out that matters.

We focus on the intake of caloric energy because it is easy. Simply measure what you eat in a day, add up the calories and boom. You have your answer. To understand what is going on with total energy expenditure (TEE) is much, much harder. That’s why we don’t think about it and make the erroneous assumption that it is constant.

Let’s consider the TEE of a person who is obese. Many people assume that they have ‘slow’ metabolism. In other words, the TEE is low and therefore, for the same amount of calories, this person will be prone to weight gain. This is the familiar calories in, calories out model.

For example, Adam eats 2000 calories a day and TEE is 2000 calories. Fat is neither gained nor lost. Zeke eat 2000 calories a day but TEE is 1500 calories. 500 calories of fat are put away into storage.

So, is the problem that obese people have a low TEE? Let’s look at this article “High energy expenditure masks low physical activity in obesity”. In this study, lean and obese subjects had their Total Daily Energy Expenditure (TDEE) measured by doubly labeled water, Resting Metabolic Rate (RMR) by indirect calorimetry and activity energy expenditure (AEE) or ‘exercise’, measured by multisensor activity monitors.

Sounds very difficult and even a little painful. So what were the results? Did obese subjects have a ‘slow’ or ‘low’ metabolism? Ummm… no. Actually quite the opposite. Lean subjects had a mean TDEE of 2404 calories while the obese had a mean TDEE of 3244 calories. The obese subjects also spent less time in ‘exercise’, but despite this, had a much higher TDEE. What gives?

The obese subject’s body was not trying to gain weight, it was trying its darndest to lose weight. The body was trying to burn off the excess energy. So, then, why are the obese… obese? Over time, their body should return to leanness. The short answer is that the Caloric Reduction as Primary model is incorrect. A scale is the wrong way to think about how the body handles energy.

The body acts much more like a thermostat. There is a specific Body Weight Set Point and the body tries to maintain that set point. The proper question, then is not how many calories we eat or not, but what adjusts the Set Point? In other words ‘What makes us fat’ or “What is the aetiology of obesity?”

We can also see from this example that there is quite a variation in the TEE from one person to the next. In fact, somebody can have a TEE 50% higher than another. What causes this? Do foods and eating behavior have any influence on this? We will consider this in further detail in future posts.

Assumption#2 Conscious Control of ‘Calories In’

The second assumption is that ‘calories in’ is under conscious control. We somehow ‘know’ how many calories we are ingesting. We can choose to eat or to not eat. Hunger is merely an inconvenience and plays no part in weight homeostasis (maintaining a stable weight). It is the conscious brain that makes the decision to eat or not, based on calories.

We already know that this assumption is not true. There are numerous interacting hormonal systems that tell our body when we are hungry and when we are not. Leptin, ghrelin, cholecystokinin, peptide YY are only some of the most obvious examples of hormones involved in hunger and satiety. Clearly, it is not merely the brain’s ‘decision’ to eat or not, but a complex hormonal balance.

If the decision to eat or not was purely a conscious one, then primitive tribal peoples should have seen numerous examples of both super obese and super skinny people because they did not even know what a calorie was (imagine that!). In fact, primitive peoples had virtually no obesity, even in the face of abundant food. Knowing caloric intake or the caloric value of food is not necessary to maintain a healthy weight. Until recently, we talked of foods that made us fat or thin, not calories.

This, of course, should have been entirely obvious. Consider this. We eat about 2000 calories a day. Over the course of 1 year, we will have eaten about 2000*365 = 730,000 calories. If we gain about 1-2 pounds per year of weight, that is roughly 7000 calories. So that is only an error rate of 0.00958.

In other words, we match our calories in and calories out to an accuracy of greater than 99%. This is because each and every one of us counts every morsel of food we eat, and calculate our TDEE and decide whether we should eat that extra string bean? We are designed to eat until our bodies tell us to stop, not to fulfil some caloric quota. It is important to understand hunger and satiety signaling and its hormonal control. Instead, the Caloric Reduction as Primary (CRaP) model ignores this and assumes that all eating is under voluntary control.

That is simply ridiculous. Obviously, there are automatic systems in the body that tell us when to eat, what to eat, and how much energy to expend in exercise, basal metabolic rate etc. It is just like assuming that we need to consciously tell ourselves when to breathe, and if we forget, we are likely to asphyxiate. No, that is just wrong.

Assumption#3 Conscious Control of ‘Calories Out’

The third assumption is that ‘Calories Out’ is under conscious control. We control how much exercise we do, and we assume that everything else is stable. This makes the assumption that exercise consumes a major proportion of our daily energy needs. We often assume that “Diet and Exercise” means that diet and exercise are 50-50 partners in weight management.

Consider that a person who does no exercise at all still requires almost 2000 calories/ day. If you have ever looked a calorie counter on a treadmill, you may have noticed that after about 45 minutes of a brisk walk, the amount of calories burned is usually something on the order of 150 or 200 calories. In other words – not even 10% of our daily caloric needs. The other 90% is what we should concentrate on.

Most of our daily energy expenditure is used for generation of body heat and other metabolic housecleaning (Basal Energy Expenditure). Assuming that this is a stable and unchanging over time, we ignore it. We assume that the only variable that changes is the energy expended in voluntary exercise/ activity. We shall soon see that this is also not true. Basal Energy Expenditure is not stable and can change up or down 50%.

Continue to Calories Part IV here
Begin here with Calories I
Click here to watch the entire lecture: The Aetiology of Obesity 1/6 – A New Hope

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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