Insulin response and changes in composition of non-esterified fatty acids in blood plasma of middle-aged men following isoenergetic fatty and carbohydrate breakfasts

It was previously shown that a high plasma concentration of non-esterified fatty acids (NEFA) persisted after a fatty breakfast, but not after an isoe nergetic carbohydrate breakfast, adversely affecting glucose tolerance. The higher concentration after the fatty breakfast may in part have been a res ult of different mobilization rates of fatty acids. This factor can be inve stigated as NEFA mobilized from tissues are monounsaturated to a greater ex tent than those deposited from a typical meal. Twenty-four middle-aged heal thy Caucasian men were given oral glucose tolerance tests (OGTT), and for 2 8 d isoenergetic breakfasts of similar fat composition but of low (L) or mo derate (M) fat content. The composition of NEFA in fasting and postprandial plasma was determined on days 1 and 29. No significant treatment differenc es in fasting NEFA composition occurred on day 29. During the OGTT and 0-1 h following breakfast there was an increase in plasma long-chain saturated NEFA but a decrease in monounsaturated NEFA (mug/100 mug total NEFA; P<0.00 1). Between 1 and 3 h following breakfast treatment differences occurred fo r total saturated and total monounsaturated fatty acids (<mu>g/100 mug tota l NEFA; P<0.05), expressed as an increase in 18:1 and decreases in 16:0 and 17:0 in treatment M relative to treatment L (P<0.05). Serum insulin attain ed 35 and 65 mU/l in treatments M and L respectively during this period. Ne gative correlations were found between 16:0 in fasting plasma and both wais t:hip circumference (P=0.0009) and insulin response curve area during OGTT (within treatment M, P=0.0001). It is concluded that a normal postprandial insulin response is associated with a rapid change in plasma saturated:mono unsaturated NEFA. It is proposed that this change is the result of a variab le suppression of fat mobilization, which may partly account for a large di fference in postprandial total plasma NEFA between fatty and carbohydrate m eals.