Monkeys (more precisely chimpanzees) do not have fasting mechanisms. They never start fasting and go into ketosis, they just die from starvation after week or two. In tropics they have food available all year. They never venture far from food sources.
Humans (and other non-tropic animals like mice) have adaptation for seasonal food availability, and can go through extended fasting.
This should be higher up. Humans split from primates (including chimpanzees) roughly 5 million years ago. Early hominids only evolved the ability to store large amounts of fat and fast for extended periods of time in the Pleistocene, less than 2 million years ago. Any study done on calorie restriction using monkeys has a serious caveat. Mice offer a much better starting point for comparing metabolic activity.
You're kidding, right? I can see saying neither one tells you much about human beings, but saying monkey studies aren't relevant to human but mouse studies are just sounds bizarre.
If you're specifically studying something that is a stark difference between other monkeys and apes on one side and humans on the other, studying monkeys and apes is obviously not a smart thing to do.
> Five healthy rhesus monkeys, three male and two female, weighing from 2.4 to 6.1 kilos, were fasted for periods of 2 to 4 days... With one exception, the monkeys developed a ketosis within 2 days
Note that ketosis != fasting; ketosis == low carb, which can also be induced without fasting (but only by eating a low (near zero) carb diet). So are you sure you're not conflating 2 dimensions (how much we eat, vs what we eat)?
Funny enough, one of the reasons I respect Peter Attia, is that he's changed his mind several times, after new information came to light (i.e. he had an initial assumption based on weak evidence, then changed his opinion after he found stronger evidence). This is quite rare in general, an even rarer among the "influencers" (a.k.a. professional grifters).
The first time Peter Attia had to change his mind, is when his Nutrition Science Initiative (NuSI) collapsed. Long story short, his hypothesis was that carbs (or rather, the insulin response) make people obese, and that low carb diets drastically improve health. NuSi funded proper experiments to test this, i.e. they provided calorie-matched low-carb and non-low-carb diets. They failed to confirm the hypothesis.
Since you showed up on a Google alert (I co-founded NuSI with Peter) I'll respond.
NuSI funded two trials that could test the energy balance hypothesis. (This is an important point: these experiments tested the null hypothesis, which was energy balance, although the experimental tests were based on predictions made by the carb insulin model.) One trial, led by Kevin Hall and Eric Ravussin, was a non-randomized pilot study that they interpreted as consistent with the energy balance hypothesis. That interpretation was challenged by David Ludwig who led the other trial, an RCT that Ludwig interpreted as inconsistent with the energy balance, calorie-is-a-calorie model. Hall et al challenged that interpretation.
If Peter changed his mind, which his book suggests he did, it could not have been based on the results from the NuSI-funded trials because their interpretations were contradictory, as experiments in science often are. Peter cares deeply about scientific method so I'm sure he understands this.
Humans (and other non-tropic animals like mice) have adaptation for seasonal food availability, and can go through extended fasting.