Acute metabolic responses to meals containing various amounts of carbohydrate and fat.

Mounting evidence indicates that acute physiological responses to individual meals are very important in determining and managing disease risk. Because the metabolic response to a meal is largely dictated by its macronutrient content, evaluating responses to meals containing various amounts of carbohydrate and fat is very important when assessing how diet can affect metabolic health and disease risk. The studies of my dissertation were designed to investigate the effect of the acute ingestion of fat and carbohydrate on physiologic measures associated with changes in metabolic health and disease risk. In Study 1, the elevation in plasma triglyceride concentration in the hours after a high fat meal was greater in men compared with women because of a prolonged availability of the ingested lipid within chylomicrons. Building on this finding, in Study 2, the addition of carbohydrate to a fat meal reduced the bioavailability of ingested fat into the systemic circulation similarly in men and women, but total plasma triglyceride concentration was attenuated by adding carbohydrate to the meal in women but not in men. Our data suggest that, in men, perhaps an increased contribution of an alternative source of fat (e.g., fat from a previous meal) to total triglyceride levels may help explain why adding carbohydrate to the fat meal did not reduce the lipemic response. In Study 3, one day of physical inactivity slowed the removal of triglycerides from the circulation in both men and women, but women appeared to respond more robustly to the effects of physical inactivity on plasma triglyceride concentrations. Finally in Study 4 (a paradigmatic mirror of Study 2), the removal of fat from a meal accelerated delivery of exogenous carbohydrate into the systemic circulation, without altering plasma glucose concentration. Therefore, the liver must have reduced glucose production proportionally to the accelerated rate of exogenous glucose entry during the first hour after the meal in order to maintain plasma glucose concentration. Together, the findings of this dissertation provide important insight into the interrelationship between the content of fat and carbohydrate in a meal and their affect on acute physiologic measures that are associated with metabolic health and disease risk.PhDHealth and Environmental SciencesNutritionUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126743/2/3276210.pd