Origins of Fitness: Why People Get Fat

Stupid, lazy, and ugly. Those are the three adjectives most commonly paired with the word fat in the English language, making these particularly unpleasant times to be overweight. Not to mention hazardous. For the first time in our history, we have reached the point where most people in the world alive today will die from being too fat – its close correlation with a host of chronic diseases including heart disease, cancer, diabetes, and hypertension means that obesity has overtaken even tobacco and alcohol as the leading avoidable cause of premature death worldwide. 

So let’s cut to the chase here – if obesity is avoidable, which it almost certainly is, and if its consequences are so dire, why are there so many fat people? 

The official story is based on what I call the Drunken Sailor Theory, likening the way a fat person consumes food to the way a drunken sailor spends money – rashly, imprudently, and without a flicker of a thought to tomorrow. 

It’s a persuasive theory partly because it draws upon the scientific thinking of the unassailable Professor Einstein, the man who proved that “energy cannot be created or destroyed, it can only be changed from one form to another”. Since fat is just the storage of excess energy, the reason why people get fat must be because they are consuming more energy than their bodies require. Case solved.

The Drunken Sailor Theory very much underlies the global obsession for counting and cutting calories. The nutrition facts label, a label now required on every single item of food we buy, starts by telling you its calorie content. The first bullet point in the 2015-2020 Dietary Guidelines for Americans, arguably the most influential text on how to eat in the world, implores readers to “choose an appropriate calorie level to help achieve and maintain a healthy body weight”. Not to be outdone, Public Health England’s 2018 health report manages to get the word into its actual title: “Calorie reduction: The scope and ambition for action”. 

The new U.S Nutrition Facts label, announced in May 2016

Notice in the new label the emphasis on calories becomes even greater than before

And the theory even lends support to those cruel associations of being lazy (why don’t fat people just do some exercise?) and stupid (why don’t fat people just stop eating so much?). 

Persuasive, pervasive, and pernicious. But deeply flawed. The use of the calorie model as an explanation for overweight and obesity is a textbook case of confusing proximate and ultimate cause. Just as we would mock the person who explained why a room is full of people by saying that more people had entered the room than left the room, so should we ridicule the person who attempts to explain why somebody is fat by saying that they had consumed more energy than they had expended. Both statements are valid in the sense of being mathematically true, but barely relevant at all to the understanding of what actually caused those situations to come about. Of course the fat person has consumed more energy than they have expended, the question is why?

Let me put forward an alternative story which is based on what I call the Blind Beggar Theory. Imagine for a minute our fat person behaves not like a drunken sailor but more like a blind beggar – as careful with money as anyone, in fact frugal to the extreme, but deprived of the most important of all of the senses for the careful handling of notes and coins – sight. 

“Nothing in biology makes sense except in the light of evolution,” said the great geneticist Theodosius Dobzhanksy. Would we explain the height of a giraffe or the mass of a blue whale by saying they had consumed more calories than they expended? Such talk would be absurd. To understand why people get fat, we need to understand how we evolved. We need to look at why we store body fat in the first place and we need to understand what happened to the mechanisms managing our fat storage.

In the beginning, fat was the answer to our preeminent survival crisis. When humans first evolved around two million years ago, our biggest threat was an energy balance problem. Of course every animal has an energy balance problem to solve, but ours was made particularly acute because we were saddled with such an enormous brain. All those things which would eventually allow us to rise to the top of the food chain – the development of language, social networks, the ability to solve complex mathematical and engineering problems – they were only enabled by having a big brain. But in the beginning our brains contributed almost nothing to our ability to obtain energy and yet were responsible for one quarter of our energy consumption. The evolutionary gamble was compounded by the fact that even a temporary shutdown of energy supply to the brain meant instant death. Faced with this type of burden, how could we ensure a constant supply of energy to the brain even through periods of food scarcity? Fat. 

Our energy balance problem is particularly acute due to the enormous size of the human brain, responsible for one quarter of our energy consumption

At 15% body fat, human infants have the highest body fat levels of any mammalian species. Human infants continue to gain body fat during their early postnatal life to around 25% before settling back down in adult hunter gatherers to about 10% in males and 20% in females – low for modern human standards, but in fact much higher than most other primates. The significant discrepancy between male and female adults reflects the fact that female humans not only need to store fat to meet their own energy requirements, but also as an energy reservoir for potential pregnancy and breast feeding.

Adult hunter gatherers have body fat of 10% in males and 20% in females

But of course, having a high level of body fat in itself was another huge evolutionary gamble. A fat animal, as well as being a particularly juicy target for predators, is a slow animal. And a slow human would not have survived long enough to produce descendants. We are all therefore, without exception, descended from humans who developed robust self-balancing mechanisms to prevent the body from ever exceeding healthful levels of body fat, even during times of abundance. When you feel hungry, what you hunger for, what foods you choose to eat first when presented with a selection, how much you eat – these are far from random occurrences. They are the result of a complex interplay between hormones and the nervous system which evolved over millions of years to ensure our survival. 

Our self-balancing mechanism for fat storage relies heavily on a single hormone, leptin, which controls hunger. The more fat cells the body has, the more leptin we produce, thereby greatly diminishing our appetite for food and eliminating the possibility of gaining excess fat. For two million years, this mechanism functioned perfectly. Then something unexpected happened. The leptin mechanism broke down because it started to be blocked by another hormone – insulin, the metabolic hormone which regulates energy metabolism. Insulin is produced whenever blood sugar levels rise and allows the body’s muscle and fat cells to uptake glucose from the blood stream. It also temporarily blocks leptin from working because it needs your body to store energy in fat cells, not use your fat cells as fuel.

During the two million year period of history when we were hunter gatherers, this relationship between insulin and leptin was not problematic because our insulin levels were never elevated for long periods. The Paleolithic diet was a fat predominant, low carbohydrate diet. The bulk of our energy supply came from eating animals, and even the plants which we ate were either starchy in-ground sources such as roots and tubers, or above-ground fat sources such as coconuts and palm fruits. Sweet fruits were incredibly rare. Although there was no doubt a significant degree of variation in the dietary intake of indigenous populations in warmer and colder climates, one thing of which we can be certain is that entire categories of carbohydrate-rich modern foods – sugars, grains, and dairy, were completely absent from the Paleolithic diet.

Understood correctly, the problem of obesity is therefore what Harvard anthropologist Dan Lieberman would classify as a mismatch disease. Our hunter gatherer bodies have a perfectly adequate mechanism for avoiding obesity when we consume a hunter gatherer diet. The problem is we have stopped eating a hunter gatherer diet. 

The Paleolithic diet was a fat predominant, low carbohydrate diet consisting of meats, fish, eggs, nuts, fruits, and vegetables

When considered from an evolutionary perspective, the idea that people get fat because they have got their calorie calculations wrong is not only nonsensical but completely incompatible with numerous phenomena we observe in the natural world, the most obvious of course being the absence of obesity in every other animal species. There is not a single animal in the world which has been observed to eat itself to the state of obesity even during times of abundant food supply and a total absence of threat from predators. Researchers attempting to induce obesity in animals under laboratory conditions have scratched their heads wondering why it doesn’t happen. Tellingly, the only ‘successful’ cases of where we have induced obesity has been in the case of zoo animals and human pets – animals who no longer consume the foods they evolved to eat but instead eat foods manufactured by humans. 

An obese siberian tiger in a China zoo 

Then there is the other obvious anomaly. If, during the last few decades, we suddenly started getting our calorie calculations wrong either through shameless gluttony or sheer idiocy, how on earth did we ever manage to keep obesity levels so low before that? Are we to assume that at the point where the food industry started manufacturing and marketing foods chock full of sugars and refined carbohydrates the human population was also infected by a plague of laziness and stupidity? 

Trends in obesity among adults aged 20-74 years: United States, 1960-2008

Of course the idea that what you are eating might be more important than how much you are eating is hardly something new. It was first put forward in 1878 by Max Rubner, the first man to show that the law of energy conservation holds in living organisms. Even after proving that “a calorie is a calorie” by studying the heat expenditure and respiration of a dog for 45 days, Rubner observed that “the effect of specific nutritional substances upon the glands” may be more important than the quantum of energy consumed. How prescient those words would turn out to be.

German physiologist and hygienist Max Rubner

The real reason why the Drunken Sailor Theory continues to be propagated is because anything else would be a threat to the food giants who rely on sugary food products and beverages for their profits and who wield such devastating influence over public policy. Pin all the blame on the consumer for consuming too much and we can escape the awkward truth that the only way any animal can consistently overconsume is when its body has been poisoned. A colossal mismatch exists not only between our bodies and the modern human diet but also between the advice we are being given and the advice we need to address the problem. For as long as we continue telling people to reduce their calorie consumption, we will have as much success as telling the blind beggar to be more careful counting his notes and coins.

About the Author 

Victor Rowse is a fitness researcher and personal trainer based in Beijing, China. He works with numerous celebrity clients including Yao Chen and Li Jian, with whom he has also produced a series of workout videos. Victor holds a Master of Arts Degree in Philosophy, Politics, and Economics from Oxford University, UK.