I don’t think this is necessarily a priori true. The body could excrete food without digesting it, or increase metabolic rate and burn calories as waste heat. But regulation of appetite is the most obvious and efficient means to reduce effective calorie intake, and we know that mechanisms to regulate appetite do exist and could easily be modulated by natural selection (what is appetite other than a regulatory mechanism for food intake?). So I agree you’re probably right - appetite is where any regulation would likely take place, and appetite is where dysregulation is most likely happening.
There’s no mention of forcing the animal to eat, and people who weight 1000 pounds didn’t get that way eating salads, they eat carbohydrate and sugar laden foods to gain that much weight. The times I’ve seen their diets discussed it was heavy on pizza, hamburgers, and sugar laden drinks and dishes. As far as I know they also need someone to provide them with that food. I don’t think the situations are really different. And any control mechanisms that exist may not work with such ‘non-natural’ diets.
There is also a control theory question–assuming body weight (or fat excess, etc.) does play a part in appetite, how exactly does it go about it?
At the simplest level, we can distinguish between proportional (P) control vs. proportional-integral (PI) control. Proportional control would only take the current weight excess into account, and dial back weight based on that. PI control however would take the current weight excess and the excess over time into account. So it could in addition dial appetite back further if the body saw that there was an excess over an extended period.
P control is prone to inevitable bias, however. If there is some error between the measurement and the response, you will not end up at the equilibrium you wanted. If the body undercounts calories (because modern foods are too calorie-dense, for instance), you will end up at a higher weight equilibrium than the setpoint.
A PI controller would see this continued excess and dial appetite back further to account for the error. But it’s not obvious that the control system that the body uses has an integral input.
The body does a very good job of controlling complicated pathways using many forms of feedback control. Some of the pathways are well understood, others may be unknown.
Despite popular understanding, it would be very difficult for you, now, to intentionally put on one hundred pounds over the next two months or even a much longer time. You would not want to eat that much, and would stop. If forced, when you did the weight actually gained would be far less than predicted. This is because the body, naturally, does stop putting on weight. It does not much like the setpoint being decreased. But it does not care for increases either. Far less than you would think.
Indeed there is not. “Forcing a system into dysregulation” does not mean force feeding. It means any kind of articifial environment (such as availability of unnatural high-calorie foods or limitation on physical activity) that the system was not designed to regulate because those circumstances do not occur in nature.
Newer foods are designed to addict our primitive brains. Quantities may be unlimited, but common sense is not. People can choose healthy foods which taste great, contain more fibre, and provide more satiety. They can usually choose to move more as well.
I wonder how many lives have been saved by the decision of many governments to greatly reduce or eliminate the amount of trans fats in food. What other changes are worth making?
Which is correct.
Our current environment is a very abnormal one with the scope of human evolutionary history, broadly obesigenic like no other time. Oh particular individuals previously had individual environments that were obesogenic, but not broadly like we currently have.
These factors include wide exposure to foods with very high hedonic value (hits brain pleasure center hard) coupled with very low satiety value (does not hit the filled up brain center hard). Think Oreos, soda, chips … versus apples, nuts, boiled potatoes, roasted meats …) And it includes built in movement that we have less of in general.
Put an unlimited amount of bananas in front of you one evening, and an unlimited amount of Oreos another. For the former you will stop eating at fewer calories in than the latter.
The modern environment often overrides the controls that prevented obesity most of the time through most of history, including in times of plenty.
Maybe… maybe not.
If having active grandparents helping to care for you would provide a survival advantage for young, growing children before reproductive age then, in fact, survival beyond early reproductive age might matter. For a slow-maturing, care intensive species like humans that could be a factor. It might be a reason for menopause in human females (stopping the risk of death in childbirth for older women, and also freeing them up from caring for their infants to caring/providing/helping with their descendants’ children), and it also might be a factor in why humans live about twice as long as their closest ape relatives. This would also apply to human males, who invest far more energy in their offspring than most male mammals, and who likewise can continue to help raise their offspring’s offspring into old age if they remain healthy and active.
It would be relatively new and subtle, but such a pressure could exist in the human species. Thus, genes leading to a longer, healthier old age might be favored over a very, very long term.
As for food, eating, weight, and fat/obesity - I see some strong cultural factors at work as well. Many cultures have cultural practices involving self-control regarding food such as fasting, what to eat and when, and so forth. They are far from perfect, of course, but they do exist.
I really do believe that there are some mechanisms in place to regulate appetite in humans. For an example of what happens when there isn’t see Prader-Willi Syndrome, a genetic disorder where the sufferers are always hungry no matter how much they eat. While weight can be controlled with VERY strict protocols (including locking up food) it’s not at all easy. The fact the rest of us don’t struggle like this indicates that there are, in fact, mechanisms to control appetite and weight gain in normal humans. If they don’t work as well as we’d like it’s probably because they are poorly fitted to our current environment of abundance, but they do exist.
Saw an obese snake last night! We noticed a drop in egg production from our hens from ~3 a day down to 1-2 a day. The nest boxes are situated to make them difficult for all but incredibly long snakes to reach.
Last night my gf rushed me down to the barn, where a ~7 foot long Central Rat Snake (Pantherophis spiloides) was devouring eggs. He’s been eating an egg or two daily for a month, and was obese (my gf pointed out that I eat an egg or two a day). I caught him easily and we got him into a feed sack, then took him for a drive, releasing him 5 miles from home.
We love having snakes in the barn, controlling rats/mice without traps or poison, but he was way too big.
In fact, it looks like we humans have a whole host of physiological mechanisms evolved for this sort of thing. So it’s not only easy for us to pack on weight when there’s abundance, it’s also hard to lose it.
Clearly at some point in our past history as a species, some ancestors must have faced some kind of seasonal scarcity that was severe enough and prolonged enough to evolve these sorts of mechanisms.
That said, I’d be willing to bet that back in the day, people just got a little bit chubby by the onset of winter, not some sort of 42 BMI fatness as a result of these mechanisms. Not that they couldn’t, but that food was never SO abundant that they’d be able to get that fat over time (it doesn’t happen in one summer).
But now, in the days of super-abundant, super-caloric food, those mechanisms kind of work against us- our bodies are acting like we’re going to have lean times in the winters, but we can consistently eat more calories than we burn off, so we just get bigger and bigger.
I saw a thing while in Alaska about bears; the ones that live on the coasts where the salmon run are CONSIDERABLY larger and fatter than the ones that live inland and mostly live on berries/fruit/smaller animals.
For example, a bear named “747”, got so fat in 2020 that his belly dragged the ground, due to a combination of a record salmon run, and a lot less tourist fishermen for competition. They said he was fat enough to hibernate as early as July.
The two circumstances were the same, no force feeding but unlimited availability of unnaturally enriched foods. However, I don’t think that kind of test needs to be done.
To sum up, I concur with others who think there was no need to evolve a specific mechanism to keep animals from gaining so much weight they would end up with a reproductive disadvantage. I do think that our that there is a systemic protection from such overeating that is not perfect but doesn’t need to be because long term excess food availability is rare. I also think that systemic protection evolved over a very long period of time starting with the simplest animals from which our digestive and fat storage process.
Gotta remember - we’re actually tropical animals. For most of our evolutionary history we didn’t experience winter. What we probably had was episodic feasts. Day to day we lived on gathered fruits, nuts, and vegetables, quite a few of which we had no way to preserve so they had to be eaten quickly. Every so often the men would bring down a prey animal (or perhaps we’d come across something we could scavenge) and we’d stuff our faces with that… but we might not see more of the high fat, high protein stuff for weeks thereafter. So being able to cram in food when it was available and convert it to longer term storage really would have been an asset even if the feast/famine cycle was measured in days or weeks rather than months. Which probably accounts for why there is nothing that we MUST have every single day without exception (except perhaps water) but some vitamins we don’t store more than a few weeks (like vitamin C) - because we need some storage, but nothing that required months of it. Unlike animals that hibernate or at least significantly cut back on winter activity, like bears, which are much better at both putting on fat and utilizing for long-term needs than we are.
No doubt our ability to pack on fat had some use when settling more seasonal climates, and it probably helped in the South Pacific which, even in the tropics, tended to have boom-bust cycles of food. But a lot our adaption to seasonal food sources and temperate to arctic climates involved culture and technology (clothes, coats, food preservation) more than physical adaptations.
I’m not quite sure I’m understanding the distinction. We do have an appetite that affects our drive to eat. It is surely based on many factors, including how long it’s been since we last ate and the immediate availability of food. And surely it is tuned (with some exceptions that we can classify as disorders) so that we don’t waste away to nothing or gorge ourselves until we’re physically unable to move.
My suspicion is that our appetite is largely fixed, at least for a given environment; that for a typical adult male it tries to get 2000-2500 calories in us per day, which leads to a reasonable equilibrium. But since our body cannot measure calories directly, it has to do so based on little more than volume and taste. And hence when we eat an extremely rich diet instead of one including a lot of plants and lean meat, that same person ends up eating 3000-4000 calories and keeps getting fatter until their base metabolism equals their food intake.
In this sense, there is a mechanism preventing us from gaining too much weight–a fixed food intake allows some variation in the final equilibrium weight, but not enough that a normal person would reach 1000 lbs. With easy access to calorie-dense foods, though, just about everyone ends up on the high end of the spectrum of weights.
It is easy to pack on a little weight when there is abundance. It is not easy to pack on a lot of weight in a short time, because the body stops treating a calorie like a calorie, due to other feedback mechanisms.
Is it that, or is it just that hard to sustain a caloric excess? Appetite is a powerful motivator. One would expect that eating beyond one’s appetite is just as difficult as the reverse. Since almost everyone fails at restricting calories in the long term, I’d expect almost everyone to fail at overeating as well, including the same kind of lies and misjudging of intake.
Seemingly both. Despite popular belief and increasing obesity, it is not as easy as one thinks to eat much more than one does. Your body does not want to change weight by large amounts in any direction. It is a struggle to eat enough, and to continue to do so, and it is a struggle to keep from losing weight above one’s set point. And like running marathons, the change is less than one would predict from 3500 Kcal = one pound of fat calculations, since the body is not easily reduced to such a simple understanding.
Of course one can gain weight, gradually over longer periods of time and by choosing foods injudiciously with accompanying reduced activity. But to gain lots of weight quickly - not so easy. A common complaint of natural weightlifters is they cannot eat as much as they would like. One guru recommends weightlifters eat four fast food breakfast sandwiches daily, for calories and ease of consumption.
Is there a mass setpoint, or is there an appetite setpoint? Those aren’t the same thing, and my speculation is that it’s more the latter. People have gotten fatter because for the same level of appetite satiety they are eating more calories in the modern world. They would lose weight if they ate more plants, less carbs, and leaner meat, even with unlimited availability, but that is also difficult–though for different reasons than why it’s difficult to ignore one’s appetite (in either direction).
[typing quickly because that somehow makes it feel like less of a topic hijack] I gotta wonder about that, though. ISTM that the evolutionary increase in gestation growth to the point where neonatal head size is (usually) JUST small enough to fit through the vaginal canal means that there’s a substantial advantage in limiting childbearing to younger-age females.
A society where every woman eventually dies in childbirth because she’s “aged out” of being able to handle the extreme physical stress of childbearing strikes me as potentially a lot more precarious then a society where women stop being capable of conceiving children BEFORE they’re too old to handle the stress of bearing them. Irrespective of whether or not those postmenopausal women are caring for grandchildren.
Anyway, back to the question of natural obesity controls:
Apparently one of the physiological responses to obesity in wild animals, at least in the case of mice, is producing offspring. Use that food surplus to boost propagation of the species, and the extra effort required to provide food for the offspring tends to slim the parents down.
It seems to be both mass and appetite with many chemical intermediaries involved in each system. Though I agree with everything you said. Even something like appetite depends on many sensory cues and can be easily fooled by the colour of food or plates, spices, order in which foods are served, gimmicks like bowls of soup where the level of soup does not change, etc.
This is the subject of many clever psychology experiments. People will watch movies and eat large amounts of seriously stale (month old) popcorn although they wince with each handful. People will eat three times the normal amount of soup if the level does not seem to decrease (done through clever mechanical means). Spicier food may mean less is consumed.
There may be benefit to losing weight by eating all the proteins and fats in a meal, waiting a short time, then eating carbohydrates last. Though the amount of food is the same, the insulin levels are said to be significantly lower. All that it costs you is time, pleasure and funny looks. I have not tried it; I am not trying to lose or gain weight (though would welcome less fat). But possibly worth a try if you hope to lose weight. Let me know how it goes.
Well, I don’t need to lose any weight. I weighed 125 lbs when I graduated high school in 1996, and weighed 126.2 lbs this morning. Not once in that timeframe have I gone outside the 120-130 lb range. Though the past few days I’ve been consistently 1-2 lbs over my target and so I plan on having light dinners (which is my only meal of the day) until I drift back down to an even 125.
What has become clear to me over time is that while I don’t think I have any more willpower than the next person, my appetite response is basically negligible. Hunger is about the mildest discomfort imaginable, like being one degree too cool. The feeling is there, but easily ignorable.
But my friends and family appear to have no such luck, to the point that they become worse people when they are hungry–angry, rude, incapable of performing basic tasks, and so on. It’s obvious that appetite has an extreme effect for them, making weight management far more difficult.