Do proteins inhibit or boost your autophagy?
Eating a lot of protein, especially red and processed meat, likely inhibits autophagy via higher IGF-1 levels. If you want to stimulate autophagy, eating less and more deliberately is a more practical lever than supplements.
Proteins have a direct influence on autophagy, the process by which your cells clean themselves up and break down damaged material. The key lies in IGF-1, a growth hormone. People who eat less protein tend to have lower IGF-1 levels on average. Lower IGF-1 levels are in turn linked to a longer lifespan. This is an association in humans, not a proven causal relationship.
Not all proteins are equal. Eating a lot of red meat, and especially processed meat, has been linked to higher all-cause mortality in multiple large analyses. The amino acid methionine appears to play a role here: in animal and model-organism studies, restricting methionine extended lifespan. Whether that also holds for humans is not yet known. Caloric restriction, including intermittent fasting, is the only approach that reliably extends healthspan in mammals, including non-human primates.
Autophagy is not purely beneficial. In disease states such as cancer-related muscle wasting, excessive autophagy can contribute to loss of muscle mass. That is the downside: an overly strong or sustained activation of cellular clean-up processes is not always desirable.
Spermidine, a compound naturally present in food (wheat germ, fermented products), activates autophagy through a modification of proteins in the cell. In mouse studies it improved memory and mitochondrial function in the brain. In one large prospective study in humans, higher dietary spermidine was associated with less cognitive decline. Fly studies show that this effect depends on intact autophagy mechanisms. Note: several authors of that research have a financial interest in a company that sells spermidine, which calls for caution when interpreting those results. Effects on weight and the gut have only been studied in obese mice and have not yet been confirmed in humans.
The evidence base consists of associative human studies, animal and model-organism studies, and one prospective human study (with conflicts of interest). No RCTs are available on autophagy and protein intake in humans. Selenium and vitamin E were included in the claims but do not address the core question; they have not been included in order to keep the answer focused.