Do We Really Have No Control Over Weight?

If a person believes weight is controllable, they are motivated to control it.

Posted Feb 06, 2020

In their post, Charlotte Markey and Lori A. Sousa reassure the overweight that they need feel no guilt for their condition. I agree that guilt is unhelpful, but arguing that we have no control over our weight is even worse.

At the head of a long list of excuses is genetics. Markey and Sousa assert that 80% of our weight is due to genetics falsely suggesting that there is not much to change and that weight is largely out of our control.

The Genetic Fallacy

This is a common misunderstanding of the heritability statistic. In fact, heritability tells us nothing about the weight of an individual. It is a population statistic that tells us how much of the population variability is attributable to genetic ancestry.

Pursuing the genetic fallacy further, they argue that it is is pointless to feel responsible for our weight as it is to feel guilt over our height. This spurious argument exposes the problem of misusing heritability in this way.

The issue, of course, is that height really cannot be changed because bones are hard tissues that cannot be reduced by exercise or diet. On the other hand, overweight is caused by body fat. This tissue is designed to be changeable so that fat stored in good times can be withdrawn in periods of food scarcity.

The fact that height and weight both have very high heritability estimates but that one changes routinely whereas the other does not demonstrate that heritability, as such, tells us nothing about weight gain or weight loss.

Height has high heritability and low changeability whereas weight has high heritability and high changeability. So, as to the claim that “weight is written in your genes,” it isn't.

Various other excuses are advanced for our supposed lack of ability to control our weight.

Miscellaneous Excuses

The authors point out that most efforts at weight loss are counterproductive and often end up making people more energy-efficient and heavier.

Of course, this is true but it is a fallacy to claim that weight cannot be reduced if the only method examined involves dieting and starvation. Comparisons of people across societies suggest that diet is relatively unimportant to bodyweight because some of the slimmest populations eat the most. The reason is that they are highly physically active as is true of many indigenous people studied by anthropologists.

They point out that Americans suffer from a sleep deficit that disrupts circadian rhythms for eating and tends to increase weight. While this is undoubtedly true, sleep time is one of the most controllable features of a person's life. Simply go to bed earlier. Avoid caffeine in the evening. Shut down the electronic screens early.

Another straw man used to explain away overweight is the bacteria and other tiny organisms living in the gut (the microbiome). Our ancestors had a microbiome. They weren't overweight.

If the coauthors are taken at face value, one might imagine that the inevitability of overweight would afflict people in all societies. Yet most societies of the past had obesity rates close to zero. How was that possible?

Weight Variation Across Societies is Behavioral

Indigenous people studied by anthropologists provide a good lesson in the real causes of modern overweight. Anyone who has seen the Jim Carrey movie Ace Ventura: Pet Detective knows that the Mbuti tribe are remarkably fit and slim.

The same is true of other hunter-gatherers whose slenderness is attributable to a high level of physical activity. Skeptics of this view like to point out that these people are slim because they have trouble finding enough to eat.

Anthropologists collect detailed information on calorie intake and know that people living in a state of nature do not eat less than modern Americans. Indeed, they eat far more when their caloric intake is adjusted for their generally smaller, and lighter, bodies. For example, the Ache of Paraguay consume approximately 50 percent more than Americans.

What is true of highly active foragers is also true of farmers. In recent history, the Pima people of Arizona came to the attention of health researchers as the most overweight ethnic group in the US.

For a long time, researchers theorized that they carried a thrifty gene that favored survival in conditions of food scarcity.

Then, someone thought to study their ancestral population living as subsistence farmers in the mountains of Mexico. Contrary to the thrifty gene hypothesis, they were universally slender despite having high levels of caloric intake.

The reason for their effective weight control was the much more active lifestyle of farmers compared to the sedentary American population.

How Much Physical Activity?

These examples show that subsistence farmers and foragers were both good at regulating their body weight. Laboratory experiments on rodents showed that if they are denied the opportunity for exercise, they gain weight. Inactive populations are vulnerable to over-nutrition by high-fat and high-sugar diets. Conversely, wild animals do not suffer from morbid obesity.

All this should provide hope to those battling overweight. Weight is regulated in physically active populations. This raises the question — how much physical activity is necessary for people to maintain a healthy body weight? 

It is quite unlikely that urban people would match the physical activity levels of foragers like the Mbuti or the Ache of Paraguay that may be physically active for upwards of six hours per day. This far exceeds the half-hour per day recommended by medical experts.

In some indigenous societies, such as the !Kung people of the Kalahari desert in southern Africa, activity levels are far lower but are sufficient to maintain optimal physical fitness. One reason for lower levels of activity is that they subsist in a desert environment that necessitates energy conservation given the difficulty of locating food.

Being guided by the !Kung example, one might reasonably conclude that if urban people took two hours of vigorous physical activity per day, they might also maintain a healthy body weight and physical fitness.

Critics will be quick to point out that we do not live in a food desert but in an environment where large high-calorie meals are easily available and cheap.

Fortunately, what a person eats, or how much they eat, is relatively unimportant if they are physically active. Physically active, humans, and other mammals, maintain a steady body weight.

Conversely, being physically inactive is a recipe for putting on weight. Farmers apply this knowledge by restraining animals in pens when they want to fatten them up for sale

People Should Hope for Change

Far from having no control over our weight, as the authors claim, the capacity to maintain a healthy weight is a birthright of all physically active human populations whether it is the indigenous hunter-gatherer societies, or modern wealthy elites who maintain active lifestyles through year-round participation in sports and fitness activities.

Health researchers might consider looking at elite physical activity budgets as a way of determining more realistic guidelines for exercise.