Principles of Biochemistry, Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Lipid Biosynthesis
The biosynthesis of triacylglycerols is hormonally regulated

In normal healthy adults and animals, the Biosynthesis and oxidation of triacylglycerols occur simultaneously, establishing a specific steady state. Consequently, body fat remains relatively constant over a prolonged period, although minor temporary fluctuations may occur with changes in caloric intake. However, when CARBOHYDRATES, fats, or Proteins are consumed in excess of the body's Energy Requirements, the surplus calories are stored as triacylglycerols. The acetyl-CoA required for the actual Biosynthesis of Fatty acids and triacylglycerols can be derived from both carbohydrates (Ch. 16) and the carbon skeletons of Amino Acids (Ch. 18). The fat accumulated in this manner can later be mobilized for energy, enabling the Organism to adapt to periods of starvation (Ch. 26).

The rate of triacylglycerol biosynthesis is drastically altered by various Hormones. Insulin, for instance, stimulates The conversion of carbohydrates into triacylglycerols. In severe diabetes, impaired insulin secretion or action leaves patients unable not only to properly utilize glucose, but also to synthesize Fatty acids and triacylglycerols from carbohydrates or amino acids. As a result, the rates of fat oxidation and ketone body formation increase, leading to significant weight loss. Triacylglycerol METABOLISM is also regulated by the secretion of pituitary Growth Hormone, Adrenocortical Hormones, and Glucagon (Ch. 25).