How Dieting Evolved To Make Us Fatter

Standing face-to-face with an unrelenting obesity epidemic, in a world filled with the promise of a one-size-cures-all diet, only now are we beginning to ask whether dieting for weight loss is the answer. We are all familiar with the concept of “calories in calories out,” that weight loss is a simple matter of tipping the equation toward a calorie deficit. This idea appeals to us because it’s so simple. But for too long now, this traditional, short-sighted, calorie restricting approach to dieting has been blindly accepted as the most effective. Strangely enough, no one talks about what it actually means to spend your life in a state of caloric deficit. Why would you when calories are an omnipresent evil, hidden in every single bite of everything you wish to eat?

Upon reviewing the clinical evidence for the long-term success of dieting, researchers from UC Davis concluded that “there is sufficient evidence to recommend a paradigm shift from conventional weight management to Health at Every Size (HAES).” [1] Several years earlier, researchers at UCLA also highlighted that an estimated one-third to two-thirds of dieters actually regain more weight than they originally lost. [2]

Sure, it sounds like the old yo-yo effect, a common dieting outcome known as weight cycling, whereby dieters shed pounds when they stick closely to their intervention program and inevitably put them back on when they stop. The fact that dieting almost goes hand-in-hand with regaining weight at a later point made it clear to me that it simply doesn’t work. From a personal perspective, as a scientist, however, I was less concerned with the idea that dieting generally doesn’t work than I was curious as to why this would be the case. When I learned about “fat-overshooting,” the biological fate of your body after living with a calorie deficit, I was in disbelief as to how far we had been misled.

Weight Loss & Fat-Overshooting

Losing weight can be explained very simply, as it follows the laws of physics that govern our world (and our bodies). The longer you remain in a state of caloric deficit, the more weight you will lose. Your body can only create energy from the fuel that you put into it or from the fuel sources that it has stored away. However, as we dive deeper into the physiology of dieting, we start approaching the idea that weight is not the problem.

When your body goes through a period of rapid or prolonged weight loss, you are losing both fat mass and lean mass. This means that there is a change in your body composition, a term that loosely describes the quantity of muscle tissue and fat tissue relative to your total weight.

Now, let’s be honest about something. There is a harsh reality that nobody wants to talk about when it comes to dieting. You could ‘crack’ at any moment. It could be after a few weeks, or after several months, or even after years of dieting. One way or another, the calorie deficit that has controlled your life will come to an untimely end. But what has happened to your body in the meantime? How will it survive as you return to normal eating patterns?

Unfortunately for many dieters, living with a calorie deficit completely changes the way your body thinks. During the process of weight regain, fat mass and lean mass do not get recovered in the same way that they were lost. As explained by researchers from The University of Fribourg, Switzerland, “there is temporal desynchronization in the restoration of the body’s fat mass vs. lean mass, such that the recovery of fat mass reaches completion before that of lean mass.” [3] In other words, after a prolonged calorie deficit that leads to substantial weight loss, your body becomes primed for fat storage. This means that when you regain weight, your body favours a ‘fatty’ body composition.

An Evolutionary Explanation of Fat-Overshooting

After prolonged calorie restriction, your body’s memory of its fat stores and lean mass drives signalling for hunger and appetite. When you inevitably give in, the process of fat-overshooting begins.

Fat-overshooting sounds like a really bad deal. After going through the hardship of losing weight by following a restrictive diet, ending up fatter in the long term is not the outcome that anyone hoped for. You’re probably thinking “why would our bodies do this to us? However, thinking this way is what got us into trouble in the first place. You should be asking “why would we do this to our bodies?”

The problem is that the biological mechanisms explaining fat overshooting have been largely ignored by the dieting industry for decades. We still think about weight loss as “calories in calories out.” And we continue to prize body weight over body composition.

One of the biggest changes to your body that occurs after weight loss is a notable decrease in your total metabolic rate. This is partly because you have a lower body mass to sustain — less muscle tissue and less adipose tissue. However, your body also starts “preserve” fuel, a process known as adaptive thermogenesis. On the whole, you are burning less calories as your body adapts to its new shape.

Since everyone has a different set of genetic determinants and environmental influences, the proportion of fat mass and lean mass lost during a calorie restricting diet varies from person to person. However, it is thought that your body has a “memory” of its lean and fat compartments, which influences not only how weight is lost but also how it is regained. Regardless of individual differences, the depletion of both fat mass and lean mass sends signals out that drive an abnormally large increase in hunger and appetite. It’s logical to believe that this is what causes us to ‘crack’ — weeks, month and years of signalling throughout your body that is telling you to eat.

At first glance, you might think that this is your body working against you. You started this diet to lose weight, right? But your body has evolved to be very efficient at storing energy, not getting rid of it. It’s only in modern society, where we have a near unlimited access to food, that storing too much energy has ever been a problem. Your body is actually doing what it is supposed to do. It is rewarding feeding behaviour to ensure your survival.

If we are to ever attack the obesity problem from the right angle, we have to opt for long-term changes in body composition over short-term dieting. After your metabolic rate has slowed down due to calorie restriction, it can remain low even once you are done with your diet. In fact, your adipose (fat) tissue, which appears to have the greatest control over your metabolic rate during weight recovery, favours a slow metabolism [3]. This is because if your metabolic rate is low, there will be extra energy available to replenish your fat stores. Your adipose tissue still holds on to its “fat memories,” hoping to return your fat stores to their former glory. Again, this is your body trying to protect you from the next food drought by storing away a disproportionately high level of fat.

Here’s the final nail in the coffin for dieting. Your body will continue to tell you that you are hungry even once you start to build up your fat stores. Until you recover all the lean mass that you lost, you will feel plagued by increased hunger and appetite. So, as you eat and your body weight is recovered, excess levels of fat continue to be deposited away. This fat deposition can persist well beyond the point you were at before you even started dieting and until lean mass is fully recovered [3].

Is Dieting Really Worth It?

Before starting any sort of calorie restricting intervention, people need to be fully informed about the lack of long-term dieting success and the potentially demoralising effects of fat-overshooting. With so many promises of “rapid weight loss” and “getting the body you want overnight,” the multi-billion dollar dieting industry should always be viewed in a skeptical light. At the heart of the obesity epidemic is a lack of education about how our body responds to dieting, a failure to let go of the battle with body weight, and an unforgiving dieting industry that may never truly appreciate ‘Health At Every Size.’

[1] Weight Science: Evaluating the Evidence for a Paradigm Shift.

[2] Medicare’s search for effective obesity treatments: diets are not the answer.

[3] Collateral fattening in body composition autoregulation: its determinants and significance for obesity predisposition.

Using my experience in research and science communication, I aim to help people make better informed health decisions.

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