“Why we store fat” doesn’t make sense

May 23, 2014 by Joshua
in Fitness, Nature

You’ve heard the reason why we store fat. You probably never questioned it. Have you noticed it doesn’t make sense?

You’ve heard the following from any number of sources. Have you ever questioned it?

The reason our bodies store fat goes back to the earliest of times. Fat storage was a tool of survival for humans. When food was plentiful people ate as much as they could. The extra food was stored as fat tissue (also known in medical circles as adipose tissue). When food was scarce at other times of the year then the stored fat was used as energy. The bodies of these early humans required the stored fat tremendously for their energy source.

What is this talk of “When food was scarce at other times of the year then the stored fat was used as energy.“? Am I missing something or is getting the body to use fat for energy one of the hardest things to do? I don’t see any physical advantage to people with extra fat. Marathon runners look skinny, not fat. I haven’t studied human biology, so I’m sure I’m missing something, but I don’t see people with extra fat having an advantage “when food was scarce.”

I see that explanation applying to other species. Wikipedia says a female polar bear “loses 15-27% of her pre-hibernation weight and uses stored fats for energy during times of food scarcity, or hibernation.” In other words, without moving around, the bear uses up a lot of its weight in fat.

But our bodies can’t do what hibernators do. Our bodies don’t seem to use the fat usefully. People seem to have hard times getting rid of fat, suggesting you’d need specific circumstances to make fat useful to our ancestors. Imagine our ancestors when food was scarce. How much extra time would a pound of fat get someone? Because if people had no food at all, unlike the hibernating bear, I don’t see the fat extending anyone’s life at all, or maybe costing it time for having to carry the extra weight. Our bodies don’t seem able to use the fat.

Meanwhile, carrying fat uses energy. So I see a cost to storing fat but no benefit like “When food was scarce at other times of the year then the stored fat was used as energy.

I’m sure there’s an evolutionary reason, but the one everyone says doesn’t seem it.

EDIT: I stand corrected. It looks like humans can live on fat for a while, at least under some conditions. The man in this article, “A year without food,” lived mainly on fat (with some supplements and medical supervision) for over a year. Here’s a journal article on it: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2495396/pdf/postmedj00315-0056.pdf

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4 responses on ““Why we store fat” doesn’t make sense

  1. This argument would be valid only if “scarce” meant “no food at all” . Last time I checked, it meant more like “not enough”. If “not enough” was accepted, the quoted statement would make sense. Available food selection and the cost to access it would depend on the season so storing fat in winter would be able to compensate for some food that was only available in the other seasons, to maintain a certain level of energy throughout the year.

    • Storing fat in times of plenty in principle can supply energy in leaner times, but my gut tells me the math of how much energy is stored versus how much it releases over what time scale doesn’t work out. Obviously there are many variables, including the costs to carrying the extra weight.

      I suspect someone somewhere created a model and did the math that I didn’t. If the math checks out I’d learn something new. If it didn’t, we’d have to learn something new about ourselves and our evolutionary pasts. And possibly about how to manage our fat levels today.

  2. I’ve never heard of someone who starved to death while remaining fat, each time I see picture of staved people or starving people, I can always make out their skeletons underneath their skin, indeed not only is all the fat used, but even muscle is reduced when faced with starvation.

    • I haven’t seen many starving people. I suppose if they starve slowly they waste away as you describe. I suspect if you just deprived someone of food they might need energy to live faster than their bodies can burn the fat and other stores and die still fat. I don’t know.

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