As a person gains body fat, obviously, each additional pound is about 3600 kilocalories of metabolic energy. That’s between 1 and 3 days of fuel to run the human body, depending on activity level, body size, gender, and metabolic rate.
So, logically, a person who is carrying around an extra 100 pounds is super safe from famine, right? They have enough fuel stored for 100 days to a year…
Now, as I understand it, the issue is, the body also needs protein - essential amino acids - to replace a constant supply of them being lost and breaking down. It’s essentially a constant supply of nuts and bolts made using processes not present in the human body. (just like colonists on Mars would need a constant supply of replacement computer chips because they wouldn’t be able to fabricate them on site)
The body can catabolize muscle to get protein, but cannot get it from fat. So your actual survival time if you have nothing but water to drink and air to breath is about a month. So you actually only need enough body fat for energy reserves for a month - 30 lbs or less. That sounds about right - a man who is a “specimen” of human fitness is about 200 lbs, 10% body fat, or about 20 lbs of fat. I guess that hypothetical man can survive 30 days or so because he can also catabolize muscles for energy.
It makes you wonder why the body doesn’t use muscles more as an energy and protein storing mechanism, hypertrophying muscle tissue in people who have excess protein in their diet.
Is this about right? If you think about it in survival times without food, people who are considered “sexy” and attractive should have about the same survival time as a person who is fat. Also, of course, a muscle-man (or woman) is more likely to successfully gather wild grain or club something to eat.
because it’s indiscriminate, and there’s one really really important muscle in the middle of your chest you don’t want your body stripping protein from.
How much body fat is useful for protecting against famine depends on just how much famine you have. If you have no famine at all, as is the norm in the First World, then none of your body fat is protective, and it’s all just waste.
In a hunter gatherer (or similar) population, during times of famine most women who lose a significant amount of weight often become (temporarily) infertile as a result.
On the other hand, an obese woman member of that group may well have been infertile before the period of famine as a result of her obesity, but will become fertile as she loses weight.
In other words, obese women can keep the gene pool going during times of famine.
It actually does. Muscle mass grows during caloric excess along with fat mass. The relationship is curvilinear - meaning the first amounts of gain are a larger fraction muscle than additional gain is. The heavier one becomes the more each additional amount gained is fat not muscle. Weight loss of course also comes from both.
Fat however has more calories per stored gram. Just counting the protein vs the fat you are looking at 9 calories/gram of fat and 4 calories/gram for protein, more than twice the weight to carry around in muscle for the same calories as in fat. Plus muscle contains glycogen (same 4 calories/gram) which automatically stores with two to three times its weight of water. You’d have to carry around much more muscle weight for the same amount of calories than you’d need to carry in fat.
Also mobilizing energy from protein is a less efficient process than mobilizing energy from fat, especially during activity that is using the muscle. The process of getting energy from the body’s protein in muscles costs more energy than getting it mobilized from fat.
Lastly, the body has a limit to how much of the protein breakdown products it can safely process and get rid of. Going much very over 30 to 35% of energy from protein usually begins to cause problems.
Yes, it does seem somewhat counterintuitive. However, unless I’ve misunderstood it, this article seems to suggest there is empiric evidence for it (third paragraph in the section subtitled ‘Survival of the Fattest’).
Body fat can protect people from other factors. Fat can be insulative against low temperatures. It can also provide energy to heat your body. It cushions your internal organs. Not just against external strikes, but from regular body motion during daily life. Fat also regulates nutrients.
Probably just need 10% body fat to gain much of these protections, but extra fat beyond that can theoretically increase some of those protective factors.
This sounds like a rehash of the “Thrifty Gene hypothesis” that James V. Neel proposed back in 1962. It has since been thoroughly discredited. 25 years ago even Neel himself said “The data on which that (rather soft) hypothesis was based has now largely collapsed.”
Apparently older people with some excess weight live longer. That is one of those stats, though, that make you wonder which is cause and which is effect. Or perhaps they are both effects of some common cause. It would be nice to know which it is. But my doctor prefers that I keep my BMI about 27 (which, as it happens, is about where it is).
I have a very sick friend who suffers from constant nausea and whose BMI has dropped below 14. She has no fat at all on her and looks like a concentration camp victim. She needs a valve job, but the heart surgeon is reluctant to operate because she has no reserve. Of course, the nausea is a serious problem that no one understands at all.
Still, I don’t believe that’s quite the same thing as what is mentioned in the cited article. Again, I admit that I may be misinterpreting it, but it sounded like there is empirical evidence for what I was getting at (in Gambia, at least). To quote the link I gave above:
"His research, particularly focused on women in Gambia, in West Africa, suggests that food shortage affects fertility, and that women with the highest body weight have greater reproductive success. (Alternatively, women who become dangerously thin cease to ovulate.) "
IOW, this is not the “thrify gene hypothesis” but, rather, another way of explaining why a tendency to obesity may confer a reproductive advantage.
Well, not exactly - as noted, fat serves other purposes, such as cushioning organs and providing thermal insulation.
Also, having the energy reserve can help you survive severe illness, injury, or other short-term emergency that interferes with energy intake which, while not common, do still occur in First World people.
It also is a major endocrine organ. Too much of it causes significant dysfunction but normal amounts are part of normal function. Females get too low on body fat percent and they stop menstruating. Men will find it harder to put on more muscle mass, will experience decreased libido and low sperm production. In general the underweight are at greater future mortality risk than the moderately obese.
Moreover mobilizing energy from fat is required almost every day, not just during “famine”, including during prolonged exercise.
Too little fat is also the result of lipodystrophy and “life with too little fat can be as fraught with medical complications as life with too much fat and, bizarrely, the complications are often exactly the same.” Surreal one blogger not liking an idea scarcely makes it “throughly discredited.” The simplistic portrayal of it? Maybe. But of note different genes strongly associated with diabetes risk are very common in Asian, Mayan, and Native American populations that seem to have popped into their gene pools through interbreeding with Neanderthals and spread rapidly (called “adaptive introgression”). Why did it spread so fast even though it has only harmful effects in today’s world? Experts believe that the gene helps storage of fat when diets are very lean increasing survival and fecundity and thus had strong selection pressure to spread in the Northern Asian populations some of whom were the founding populations of North America.