In fact, it says: "Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left." That's because the body is cannibalizing muscle tissue right away, because the benefits are twofold compared to the onefold benefit of exhausting fat stores.
A lot of what we think we know about starvation comes from animal models, but the issue there is that relatively few animals are adapted to famine the way humans are, so their biochemistry isn't as tuned for absolutely last-stand, no-macronutrient survival as human bodies are, or as tuned for hair-trigger lipogenesis, either.
If famine wasn't such an evolutionary bottleneck probably more mammals would be like PEPCK+ supermice.
"And how do people lose fat without losing all their muscle first if this is the case?"
Well, they don't. People on diets typically lose more muscle than they do fat. Most nutritionists think that if you can keep the loss to 60% fat/40% muscle, you're doing really well but most people on caloric restriction go the other way and we've known that since the 70's. There's a cost function coefficient at work here, clearly; all of the Warsaw Ghetto victims did lose substantial fat reserves as they starved. But they lost muscle first, as nearly everyone does after they exhaust glycogen, and they continued to until they died from it. But the coefficient of loss, fat vs. muscle, will tend to be different for different people based on competing hormonal signals and your differing sensitivity to the signals. Muscle and fat cells compete to draw blood calories for their purposes, and they compete to donate calories, too.
It says that after this though: Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left.
So I'm very confused :) Apparently starvation is when all fat is exhausted, and protein is the only fuel source left. But also, you can die after starvation even though you still have fat. Wat?
People on diets typically lose more muscle than they lose fat: What? This also contradicts my own experience and everything I've ever heard. Most people think 25% lean loss is normal and that 40% from GLP-1 drugs is terribly bad.
It must be (I don't think normal weight loss or dieting is likely to harm anyone's heart) but the metabolic logic is more of a matter of a weighted cost function (it becomes more costly to the body to lose muscle as it loses muscle) than the hard logic of "WHILE starving, GOTO burn fat, IF fat == 0 GOTO burn muscle."
And I think one of the differences between fat people and thin people is that they have different coefficients for these functions - fat people might be people who respond to starvation by preferentially losing muscle over fat. In fact we know that if you've lost significant weight in the past, and are losing now, those cost functions in your body will have shifted so that you're even more likely to lose muscle before fat.
Yea I think it's more of a gradient, like reverse nutrient partitioning. Maybe the best case is 95% fat/5% lean loss, and the worst case the other way around. Thus it makes a huge difference how you are "starving." E.g. eating nothing at all is probably not that bad, but eating 100g carbs and otherwise nothing seems to be super bad, I remember reading a study about that. Basically, a certain threshold of carbs seems to prevent fat adaptation and then you starve real bad, whereas people who truly eat nothing, or just oil, can live off their fat somewhat comfortably.
That's not what the Wikipedia page on starvation says: https://en.wikipedia.org/wiki/Starvation
And how do people lose fat without losing all their muscle first if this is the case?
In fact, it says: "Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left." That's because the body is cannibalizing muscle tissue right away, because the benefits are twofold compared to the onefold benefit of exhausting fat stores.
A lot of what we think we know about starvation comes from animal models, but the issue there is that relatively few animals are adapted to famine the way humans are, so their biochemistry isn't as tuned for absolutely last-stand, no-macronutrient survival as human bodies are, or as tuned for hair-trigger lipogenesis, either.
If famine wasn't such an evolutionary bottleneck probably more mammals would be like PEPCK+ supermice.
"And how do people lose fat without losing all their muscle first if this is the case?"
Well, they don't. People on diets typically lose more muscle than they do fat. Most nutritionists think that if you can keep the loss to 60% fat/40% muscle, you're doing really well but most people on caloric restriction go the other way and we've known that since the 70's. There's a cost function coefficient at work here, clearly; all of the Warsaw Ghetto victims did lose substantial fat reserves as they starved. But they lost muscle first, as nearly everyone does after they exhaust glycogen, and they continued to until they died from it. But the coefficient of loss, fat vs. muscle, will tend to be different for different people based on competing hormonal signals and your differing sensitivity to the signals. Muscle and fat cells compete to draw blood calories for their purposes, and they compete to donate calories, too.
It says that after this though: Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left.
So I'm very confused :) Apparently starvation is when all fat is exhausted, and protein is the only fuel source left. But also, you can die after starvation even though you still have fat. Wat?
People on diets typically lose more muscle than they lose fat: What? This also contradicts my own experience and everything I've ever heard. Most people think 25% lean loss is normal and that 40% from GLP-1 drugs is terribly bad.
Is it just skeletal muscle that is lost first? Wouldn't nonskeletal muscle like the heart be preserved more carefully?
It must be (I don't think normal weight loss or dieting is likely to harm anyone's heart) but the metabolic logic is more of a matter of a weighted cost function (it becomes more costly to the body to lose muscle as it loses muscle) than the hard logic of "WHILE starving, GOTO burn fat, IF fat == 0 GOTO burn muscle."
And I think one of the differences between fat people and thin people is that they have different coefficients for these functions - fat people might be people who respond to starvation by preferentially losing muscle over fat. In fact we know that if you've lost significant weight in the past, and are losing now, those cost functions in your body will have shifted so that you're even more likely to lose muscle before fat.
Yea I think it's more of a gradient, like reverse nutrient partitioning. Maybe the best case is 95% fat/5% lean loss, and the worst case the other way around. Thus it makes a huge difference how you are "starving." E.g. eating nothing at all is probably not that bad, but eating 100g carbs and otherwise nothing seems to be super bad, I remember reading a study about that. Basically, a certain threshold of carbs seems to prevent fat adaptation and then you starve real bad, whereas people who truly eat nothing, or just oil, can live off their fat somewhat comfortably.