Nutritional deficiency induces a high degree of autophagy

 Autophagy is an important mechanism for generating energy (ATP) in response to stress, and it can also adjust the quality of proteins and organelles. In the hungry state, cells can be broken down by autophagy to maintain a stable cell energy level. In yeast, autophagy degrades unwanted proteins, and the amino acids produced are recycled to synthesize proteins indispensable for survival. In higher eukaryotes, when cells receive information such as lack of nutrients and oxygen, autophagy is an adaptive response that can promote cell survival. In an extreme state of hunger, the components of fat cells will begin to decompose to provide stored energy for the body to use, maintain necessary functions, and promote cell survival; eventually muscle cells will undergo autophagy to maintain the body's metabolic function. Under normal and stressful environments, autophagy can mobilize different cellular energy stores, such as carbohydrates, lipids and ferritin, to provide metabolic needs.

In a non-stressed state, continuous autophagy is essential for the conversion of intracellular proteins and maintaining a stable cell balance; this function is maintained together with UPS, another key protein degradation pathway. The protein degradation effect of autophagy can maintain the supply of amino acids and protein biosynthesis in starving cells.