Under the pressures of fasting, our cells start to repair themselves. In mitochondria, this is called mitophagy, and in the cell, autophagy (literally: self-eating).20 Rather than holding on to worn-out organelles, proteins, and membranes, cells in eukaryotes (everything from yeast to humans) can recycle their parts and use them to meet their energy needs. A lack of nutrients from food is a key trigger for this process. There are several ways this is signaled in the body. A spike in AMPK, mentioned above, is one. A drop in another protein kinase called mTOR is a second. (mTOR is a sensitive
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