While some researchers are exploring the mechanisms by which calorie restriction brings health and longevity benefits, others are looking at how overeating harms us: "Obese people have been found to harbor proteins called branched-chain amino acids (BCAAs) at far higher levels than non-obese people. The suspicion has been that these amino acids, in combination with a high-fat diet, contribute to insulin resistance. ... In the case of the amino acids, we also are finding increased levels of their metabolic breakdown products, which suggests the whole system for handling the amino acid metabolic process has been overloaded. Our rat studies show that this overload causes changes at the cellular level that can lead to insulin resistance ... Insulin resistance occurred in animals with a diet high in the branched-chain amino acids, but only if they were ingested along with a high level of fat in the diet ... BCAAs comprise as much as 25 percent of amino acids in dietary protein, and are particularly enriched in diets high in animal (meat) proteins. ... I want to be clear that our animal data suggest that there is nothing wrong with obtaining protein from sources that are high in branched-chain amino acids, as long as you are not eating beyond what your energy needs are. If you add a lot of unneeded protein to a fatty diet, perhaps that's where you get into problems. The ancient Greeks were right: everything in moderation."