Humans have evolved to gain weight

July 13, 2016

It is interesting to think about food and our relationship with it. There doesn’t appear to be any other animal in the world that consumes food quite like humans do. And based on the fact that when you get to the foundational reasons for consuming food - i.e. to sustain life and survive, it is quite perplexing that we, as humans, consume as much food as we do.


There is no doubt that we as a species have evolved for generations, including food and drink as a leisurely activity. Entire events and celebrations are based around what we can consume. And whether or not you consider yourself to be a food aficionado by preparing food yourself, humans love to eat. We derive pleasure from consuming food, especially fatty and sugary foods. When you combine the fact that food targets the pleasure centres of our brain, with our industrialization of the world, you get a lethal combination where we, as humans, live to eat rather than eating to live.


It makes sense, from an evolutionary standpoint. Our early ancestors not only needed food to survive, but craved food, especially our sugar-hungry brains. When times are good, we seem to have an endless appetite. We use the energy we need now, and then our bodies store the rest in storage (adipose tissue, aka, body fat) for times in need. The main problem with this survival mechanism is our lack of trigger to stop eating more than we need.


There have been a number of studies or theories that have come out in previous years trying to come up with a solid foundation for the mechanisms determining metabolism and fat storage. One theory, which I wrote about a few years ago called the “Set Point Theory” discusses the idea that we all have an upper and lower limit to how much weight we can easily gain/lose.


A recent review in the Proceedings of the Royal Society B: Biological Sciencesdiscusses the Set Point Theory as well as reviews some other evolutionary theories as to why we metabolize and store fat the way we do.


“To explore the logic of evolutionary explanations of obesity we modelled food consumption in an animal that minimizes mortality (starvation plus predation) by switching between activities that differ in energy gain and predation. We show that if switching does not incur extra predation risk, the animal should have a single threshold level of reserves above which it performs the safe activity and below which it performs the dangerous activity. The value of the threshold is determined by the environmental conditions, implying that animals should have variable ‘set points’. Selection pressure to prevent energy stores exceeding the optimal level is usually weak, suggesting that immediate rewards might easily overcome the controls against becoming overweight. The risk of starvation can have a strong influence on the strategy even when starvation is extremely uncommon, so the incidence of mortality during famine in human history may be unimportant for explanations for obesity. If there is an extra risk of switching between activities, the animal should have two distinct thresholds: one to initiate weight gain and one to initiate weight loss. Contrary to the dual intervention point model, these thresholds will be inter-dependent, such that altering the predation risk alters the location of both thresholds; a result that undermines the evolutionary basis of the drifty genes hypothesis. Our work implies that understanding the causes of obesity can benefit from a better understanding of how evolution shapes the mechanisms that control body weight.”


So we know humans have evolved to carry a little extra body fat at all times - women carry a bit more than men. During times of need, such as going days without eating, our bodies have a contingency plan in the form of stored energy (adipose tissue). Our ancestors didn’t have the luxury of having a McDonald’s on every corner to go grab a quick lunch, so body fat kept them going in times of need. On the flip side of this coin, we also don’t want to get too fat, because if you are too fat to run, your predator is going to catch you and kill/eat you.


Hence the Set Point Theory which states that everyone has a lower limit and an upper limit. The lower limit being the weight in which once you start to lose too much weight, your body initiates mechanisms to slow down metabolism in order to prevent further starvation potentially leading to death.


On the other hand, it is theorized that an upper limit is also set to prevent us from being too gluttonous and gaining so much weight that makes us immobile and physically prone to predation.


So what happened?


Well, the aforementioned review paper theorizes that due to our dominating position in the world, essentially removing all of our natural predators, has seemed to by-pass our evolutionary checks and balances, causing a genetic drift towards nearly unlimited fat storage.


So what is the point to all of this? Why write about it?


Well, it is interesting to think of new ways to research and potentially target therapies that prevent unneeded and unwanted fat storage. Keeping in mind that all drug therapies carry with it some sort of side-effects, we may see a future where individuals consume as they please and just pop a pill to halt unwanted fat storage.


There is an almost unending list of ethical and moral issues that can and should be discussed regarding therapies in the future. I think in the meantime, individuals who are looking to either maintain or lose weight should remember this one thing: Foods target pleasure centres in our brain. Sure, eating is enjoyable and is part of what makes us human. Having said that, remind yourself that treats or savoury foods should be kept at a minimum. Less than healthy food options, although pleasurable, are short-lived and fast acting. Instead, aim for healthier food options for longer-term health and longevity.


Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit

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