Hepatic monitoring of essential amino acid availability may regulate IGF-I activity, thermogenesis, and fatty acid oxidation/synthesis.
Diets that are low in certain essential amino acids (EAAs), whether owing to low protein content or poor protein quality, tend to down-regulate systemic IGF-I activity, boost thermogenesis, and suppress hepatic capacity for lipogenesis, while promoting hepatic fatty acid oxidation. It is proposed that for each EAA there is a regulatory protein in hepatocytes whose activity is repressed by adequate levels of its EAA; if one (or more) of these regulatory proteins is active, it serves as a signal of EAA deficiency which then mediates the aforementioned effects on IGF-I activity, thermogenesis, and hepatic fatty acid metabolism. Mechanisms which monitor EAA availability likewise play a role in appetite regulation, thus accounting for the fact that spontaneous calorie consumption tends to be lower on high-protein diets. Diets low in protein quantity or quality may decrease insulin secretion, an effect which should contribute to their impact on IGF-I activity and lipid metabolism. The fact that vegans ingest diets that tend to be relatively low in certain EAAs may play a key role in their characteristic leanness and their decreased risk for diabetes, coronary disease, and cancer.
McCarty
M F
MF
Pantox Laboratories, 4622 Santa Fe Street, San Diego, CA 92109, USA.
D000601:Amino Acids, Essential / Q000378:metabolism*; D001066:Appetite; D001833:Body Temperature Regulation; D014676:Diet, Vegetarian; D005227:Fatty Acids / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*
D000601:Amino Acids, Essential; D005227:Fatty Acids; D007328:Insulin; D007334:Insulin-Like Growth Factor I