Iāve heard that caloric restriction and castration both contribute to longevity in humans and seem (arguably?) affectively negative.
I wonder if caloric restriction would have been good for humans (or wild animals), historically. In times where you have to miss several meals (too little food, or injury/ādisease making it more difficult to get food), it seems like caloric restriction might have been dangerous. On the rare occasions where you have to spend a disproportionate amount of energy to escape predators, would caloric restriction hold you back?
The indirect harms of not eating more might also contribute to aging due to such rare events.
I find this comment a bit confusing, Iām afraid. Do you mean dietary restriction would be dangerous or that the metabolic response to DR would be dangerous? If the latter, why? Given that it seems to be an evolved fasting response Iād be somewhat surprised if it was bad for fitness overall.
I guess Iām a bit confused by the questions, too. Iāll try to explain better. I donāt think the point Iām trying to make is very deep, since I donāt have any expertise in this area.
In summary, if caloric restriction is both negative affectively and reduces aging in modern humans not living in poverty (and some captive animals), this is because evolution hasnāt had the time (or the evolutionary pressures are too weak) to get us to just want to eat less; caloric restriction (compared to how much they currently eat in the wild) probably just doesnāt reduce aging overall in the wild. Since this research is for animals living in the wild, the proposed examples of caloric restriction (in humans, and Iād add in some captive animals) and smoking not covered by the theory might not be very relevant. I suppose this might only be the case in the very long-term if evolutionary pressures still apply or in the short-term if we donāt make the lives of wild animals substantially easier. If we do make the lives of wild animals substantially easier, then biological aging might correlate less with welfare in the short-term than it had before, so it would be relevant.
To expand more:
I think we should doubt that animals eat (and our ancestors ate) more than is best for their fitness (or welfare) in the wild, since how much they eat is subject to natural selection. If eating less reduced biological aging, then this would mean that biological aging wouldnāt track some harms (to fitness and welfare) that result from eating less. But I think itās also plausible that eating less just doesnāt reduce biological aging *in the wild*, since animals probably need (and our ancestors probably needed) more energy in the wild for survival and reproduction than in captivity (than modern humans not living in poverty, resp.), where the experiments were performed. It could also be that animals eat more in captivity than in the wild because of ease of access or boredom or other environmental factors, and the amount they eat in the wild is roughly optimal for fitness, welfare and biological aging (regardless of predation, trouble getting food, disease recovery, etc.) The same could be true of modern humans not living in poverty compared to our ancestors; our ancestors were undergoing caloric restriction compared to what we eat today, but this might have been what was best for them because they had more important things to do than look for even more food.
Maybe itās the case that metabolism inevitably causes some harm, e.g. oxidation, and this harm canāt be āevolved outā, but the extra energy is worth some such extra harm in the wild, so that animals have a better chance to escape predators, or find food, or recover from disease, which are not really issues in captivity (and for modern humans not living in poverty). Spending less energy on the functions they have might be more harmful to fitness than eating less.
Maybe it would be helpful if I try to lay out my rough model of why fasting responses to limited food availability exist in the wild, and we can see if thereās actually a disagreement here.
I certainly agree that āwe should doubt that animals eat (and our ancestors ate) more than is best for their fitnessā. If they were eating more than was good for their fitness, youād expect them to evolve to eat less. However, wild animals exist in a state of severe food insecurity, in which food may be abundantly available one day and scarce for weeks thereafter. It probably is quite difficult to have offspring while food is scarce, and probably not very valuable anyway since those offspring will be food-deprived during crucial developmental periods. So it makes sense to use what energy you have to maintain a healthy body, and wait for better times.
The response to DR would therefore be a āmaking the best of a bad situationā sort of thing: from a fitness perspective it would be better to eat lots of food, have lots of offspring, and die young, but since that option is unavailable due to food scarcity it is better to activate an energy-conserving fasting response that will keep you in better shape until the good times return.
Importantly, the claim is not that DR improves fitness. It is that it increases lifespan. Natural selection doesnāt care about increased lifespan, or even increased healthspan, except insofar as it increases the number of descendents you have. And food deprivation is certainly very costly: DR mice show dramatically reduced fertility relative to AL (=eat-as-much-as-you-want) mice. However, they also show less age-related decline in fertility, so if you later put them back on an AL diet they are more fertile than mice of the same age that have been on AL the whole time. I think that summarises the evolutionary point of a fasting response pretty well.
Ok, this makes sense.
Flipping it (comparing non-fasting to fasting), not only is the extra energy when not fasting used for functions other than health/ālongevity, but further energy is diverted away from health/ālongevity towards reproduction, because the best time to reproduce is when not fasting.
If the comparison were to starvation instead of fasting, some of the extra energy would be used for basic survival. But fasting is milder.
Is my understanding correct?
I wonder if caloric restriction would have been good for humans (or wild animals), historically. In times where you have to miss several meals (too little food, or injury/ādisease making it more difficult to get food), it seems like caloric restriction might have been dangerous. On the rare occasions where you have to spend a disproportionate amount of energy to escape predators, would caloric restriction hold you back?
The indirect harms of not eating more might also contribute to aging due to such rare events.
I find this comment a bit confusing, Iām afraid. Do you mean dietary restriction would be dangerous or that the metabolic response to DR would be dangerous? If the latter, why? Given that it seems to be an evolved fasting response Iād be somewhat surprised if it was bad for fitness overall.
I think dietary restriction could be dangerous in expectation, because animals might really need that extra energy on rare occasions.
Okay, so from this I think you mean the metabolic response to dietary restriction, not the actual restriction of diet.
If thatās dangerous in expectation, why would it have evolved?
I guess Iām a bit confused by the questions, too. Iāll try to explain better. I donāt think the point Iām trying to make is very deep, since I donāt have any expertise in this area.
In summary, if caloric restriction is both negative affectively and reduces aging in modern humans not living in poverty (and some captive animals), this is because evolution hasnāt had the time (or the evolutionary pressures are too weak) to get us to just want to eat less; caloric restriction (compared to how much they currently eat in the wild) probably just doesnāt reduce aging overall in the wild. Since this research is for animals living in the wild, the proposed examples of caloric restriction (in humans, and Iād add in some captive animals) and smoking not covered by the theory might not be very relevant. I suppose this might only be the case in the very long-term if evolutionary pressures still apply or in the short-term if we donāt make the lives of wild animals substantially easier. If we do make the lives of wild animals substantially easier, then biological aging might correlate less with welfare in the short-term than it had before, so it would be relevant.
To expand more:
I think we should doubt that animals eat (and our ancestors ate) more than is best for their fitness (or welfare) in the wild, since how much they eat is subject to natural selection. If eating less reduced biological aging, then this would mean that biological aging wouldnāt track some harms (to fitness and welfare) that result from eating less. But I think itās also plausible that eating less just doesnāt reduce biological aging *in the wild*, since animals probably need (and our ancestors probably needed) more energy in the wild for survival and reproduction than in captivity (than modern humans not living in poverty, resp.), where the experiments were performed. It could also be that animals eat more in captivity than in the wild because of ease of access or boredom or other environmental factors, and the amount they eat in the wild is roughly optimal for fitness, welfare and biological aging (regardless of predation, trouble getting food, disease recovery, etc.) The same could be true of modern humans not living in poverty compared to our ancestors; our ancestors were undergoing caloric restriction compared to what we eat today, but this might have been what was best for them because they had more important things to do than look for even more food.
Maybe itās the case that metabolism inevitably causes some harm, e.g. oxidation, and this harm canāt be āevolved outā, but the extra energy is worth some such extra harm in the wild, so that animals have a better chance to escape predators, or find food, or recover from disease, which are not really issues in captivity (and for modern humans not living in poverty). Spending less energy on the functions they have might be more harmful to fitness than eating less.
Maybe it would be helpful if I try to lay out my rough model of why fasting responses to limited food availability exist in the wild, and we can see if thereās actually a disagreement here.
I certainly agree that āwe should doubt that animals eat (and our ancestors ate) more than is best for their fitnessā. If they were eating more than was good for their fitness, youād expect them to evolve to eat less. However, wild animals exist in a state of severe food insecurity, in which food may be abundantly available one day and scarce for weeks thereafter. It probably is quite difficult to have offspring while food is scarce, and probably not very valuable anyway since those offspring will be food-deprived during crucial developmental periods. So it makes sense to use what energy you have to maintain a healthy body, and wait for better times.
The response to DR would therefore be a āmaking the best of a bad situationā sort of thing: from a fitness perspective it would be better to eat lots of food, have lots of offspring, and die young, but since that option is unavailable due to food scarcity it is better to activate an energy-conserving fasting response that will keep you in better shape until the good times return.
Importantly, the claim is not that DR improves fitness. It is that it increases lifespan. Natural selection doesnāt care about increased lifespan, or even increased healthspan, except insofar as it increases the number of descendents you have. And food deprivation is certainly very costly: DR mice show dramatically reduced fertility relative to AL (=eat-as-much-as-you-want) mice. However, they also show less age-related decline in fertility, so if you later put them back on an AL diet they are more fertile than mice of the same age that have been on AL the whole time. I think that summarises the evolutionary point of a fasting response pretty well.
Ok, this makes sense. Flipping it (comparing non-fasting to fasting), not only is the extra energy when not fasting used for functions other than health/ālongevity, but further energy is diverted away from health/ālongevity towards reproduction, because the best time to reproduce is when not fasting. If the comparison were to starvation instead of fasting, some of the extra energy would be used for basic survival. But fasting is milder. Is my understanding correct?