Researchers from Penn State, published in the February 7, 2007 Cell Metabolism, have discovered that when mice are deprived of only a single amino acid, their metabolisms are fooled into thinking they are starving. In response, they stop synthesizing new fats and they use up all their fat stores, losing 97 percent of their body fat in the process.
The researchers found that a certain enzyme, called GCN2 eIF2a kinase, is the critical player that kicks the body into starvation mode. It does this by monitoring deficiencies in amino acids. Removal of just a single amino acid, leucine, from the diet of the mice was sufficient to trigger GCN2 to start a starvation response. Despite the fact that the mice were consuming normal amounts of carbohydrates and fats, they shut down fat synthesis in the liver and mobilized their stored fat deposits. Their bodies were literally tricked into starvation mode by the fact that leucine was missing from the diet.
After 17 days of a leucine-deficient diet, the mice lost 48 percent of their liver mass and 97 percent of the adipose or fatty tissue from their abdomens. The response was very similar to what happens during starvation. In contrast, control mice bred to be missing the GCN2 kinase enzyme kept a steady liver mass and lost only 69 percent of the adipose tissue on their abdomens.