Physiological modulation of plasma free fatty acid concentrations by diet. Metabolic implications in nondiabetic subjects.

OBJECTIVE: To determine the effect of varying the amount of carbohydrate and glycemic index (GI) of breakfast test meals on plasma free fatty acid (FFA) responses of nondiabetic subjects and to see whether the glycemic response at lunch was related to the plasma FFA response to breakfast.

RESEARCH DESIGN AND METHODS: We studied eight subjects over a 6-h period on four separate occasions using a randomized Latin-square design. They received isocaloric breakfast test meals that were either high (84 g) or low (41 g) in carbohydrate and had either a high (approximately 100) or a low (approximately 70) GI, followed by a standard lunch 4 h later.

RESULTS: The initial fall in plasma FFAs after breakfast was similar for all four test meals, but the extent of rebound differed significantly. The mean plasma FFA concentration just before the start of lunch (4 h) was highest after the low-GI, low-carbohydrate breakfast (418 +/- 42 mumol/l), followed by high-GI, low-carbohydrate (277 +/- 48 mumol/l), high-GI, high carbohydrate (227 +/- 32 mumol/l), and low-GI, high-carbohydrate (149 +/- 23 mumol/l) (P < 0.01). The concentration of plasma FFAs at 4 h was directly related to the total area under the glycemic response curve to lunch (r = 0.691, n = 32, P < 0.0001).

CONCLUSIONS: In nondiabetic subjects, the type and amount of carbohydrate eaten at breakfast influences the plasma glucose, insulin, and FFA responses to breakfast and also affects the glucose, insulin, and FFA responses to a subsequent standard lunch. The glycemic responses after lunch were closely related to the plasma FFA concentration 4 h after breakfast, which we speculate is due to the inhibitory effect of FFAs on insulin action.