Those of us who have been, or are obese have heard all sorts of theories as to why people are overweight. Of course there’s the perennial “favorite”, that we just plain ate too much and moved too little. /end_cynacism
Another hypothesis is that we just have too much food available, that the calorie-dense but nutritionally deficient food we have available… and available ALL the time has led to much of the surge in obesity over the last few decades. I came across an article that addresses this a bit by looking at orangutans.
Starving orangutans may explain why humans evolved to become obese - on io9.com
First off, yea, I know orangutans are apes, not monkeys… but I thought monkey made for a better headline.
Second, the article talks about how orangutans on the Indonesian island of Borneo have been isolated for the last 400,000 years and adapted to a feast/famine feeding cycle that many say our hunter/gatherer ancestors faced. So because of this, during times of plenty, the orangutans would bulk up and when times were leaner they would take to eating foods that were tougher and less nutritious foods like seeds and the starchy tissues found behind tree bark. And by studying their urine, the found during these time they were going in to ketosis – which anyone reading this probably knows from the many low-carb diets they were on at various times is an indicator that the body is burning up fat reserves for energy.
Their article is based on a study done by a researchers at Dartmouth and Rutger’s, and here’s an interesting quote they cited:
“There is such a large obesity epidemic today and yet we don’t really understand the basis of the obesity condition or how these high-protein or low-protein diets work. I think studying the diets of some of our closest living relatives, the great apes; may help us understand issues with our own modern day diets. We discovered through this research that the daily amount of protein the orangutans take in when fruit is not available is inadequate for humans and one-tenth of the intake of mountain gorillas. But it is sufficient to avert a severe protein deficit.”
I’m not sure there’s a whole lot new here, except maybe some of the researcher at Rutger’s questioning some of what’s been touted lately regarding protein intake… but one of the more interesting things I got from this posting was a comment by a user by the name of BioLady that was posted…. because I’m not sure how comments get displayed for posterity, I’m going to copy it in it’s entirety here…
oh! This is the subject I actually do research on! yay!
Now let me get my nerd on and tell you why it’s all wrong (maybe):
The hypothesis that they’re referring to- that humans become obese because our bodies are designed to store food for lean times- is called the “thrifty gene” hypothesis, and has been the standard theory for the obesity epidemic for a few decades now. The problem is, there is very little evidence that it is actually true.
A few problems with thrifty gene:
1. This is the biggest problem with the theory: why aren’t we all obese? If starvation pressure was so important in our evolutionary history, all humans should be prone to obesity. But we’re not. About a third of the population (in wealthy countries) are very prone to becoming obese, another third are a little prone- they can go either way depending on their diet and exercise level. The last third, however, are not really prone to obesity at all. I’m sure you know someone like this- they can eat pretty much as much as they want and never become fat. According to the thrifty gene hypothesis these people should have died off millenia ago. I don’t know their data, but I’m going to guess that all of the orangutans had similar fat storing abilities.2. If thrifty gene was true, you’d see members of hunter-gatherer societies (who today still live very similarly to how our ancestors once lived) gain and store weight during times of plenty. But this just isn’t seen. The BMIs of people in hunter/gatherer societies stay fairly constant (and low).
3. Famines aren’t really all that common. As far as we can tell, bad famines happen only once every 100 years or so and usually the majority of the mortality from famines is concentrated in the very old or very young.
The alternative theory I study is called “drifty gene.” It posits that the obesity epidemic is caused by genetic drift due to lack of selection pressure to stay lean. Most animals regulate their body size very closely and are not prone to obesity. If it gets too low, it’s bad for reproduction, and if gets too large than the animal can’t move very well, and becomes more vulnerable to predation. Humans, on the other hand, have been freed from any serious predation pressure for around 2 million years, so this new hypothesis suggests that the genes that control the upper body limit in humans have simply drifted over time. That explains why not all people are prone to obesity.
ok that’s it.
I apologize for my probably boring rambling nonsense.
This whole “drifty gene” theory is one that I’ve never heard of… but it may be worth looking more in to. If there is something to the science behind it… who knows, maybe it could lead to some sort of non-surgical treatments or even prevention….? Either that, or we need to get invaded by alien Predators to drift our genes back the other way. I’d be interested in hearing what others think…
image credit: one of mine from a Como Zoo trip
