Physiological Considerations of Lipid Storage and Utilization

Abstract

Normally, rats and mice eat chow-type rations. When fed such a ration, body fat usually ranges between 11 and 18%. If a semi-purified diet high in fat is fed instead of the chow-type ration, some strains of rats and mice respond by accumulating abnormal amounts of weight and fat. Their bodies now contain as much as 40% fat and fat depots are enlarged. Rats which respond to a high fat diet with excessive weight and fat gain consume more kilocalories in the same time interval and are more efficient in energy utilization than rats of the same strain which consume a grain diet. For these rats, if medium-chain triglycerides are substituted for the long-chain triglycerides in the high fat diet, there is a depression in food intake, accretion of body weight and fat as well as energy utilization. Blood makes up 3.5 to 5.1% of the fat organ weight. The lower value represents the quantity present in adipose tissue of obese rats while the higher value is for “normal-weight” rats. The triglyceride content of perirenal and epididymal fat depots is around 90%. On the other hand, the triglyceride content of inguinal fat tissue ranges from 56 to 80% and is affected by strain, age and diet. If diets are high in fat, the proportional distribution of fatty acids in the adipose tissue reflects the proportional distribution in dietary fat, except when medium-chain triglycerides are fed.