The influence of variations in amount of carbohydrate in the diet (45 per cent or 65 per cent of total calories) and source (sucrose or corn syrup) on plasma insulin and glucose concentrations was evaluated in eight normal men. Four diets, which were alternated in a Latin square design, were consumed for 10 days. Plasma glucose and insulin concentrations were measured during an oral glucose tolerance test and over a 24-hour period while the test diets were consumed. The 24-hour study was completed with a portable, constant withdrawal pump, which allowed samples to be collected as a series of 48 consecutive, integrated, 30-minute samples. Thus, the 24-hour mean, or integrated, concentration as well as fluctuations during the day could be determined.

The 24-hour integrated concentration of glucose did not vary significantly with the dietary changes tested. In contrast, two of the three methods used, to evaluate the glucose tolerance test results indicated that high carbohydrate diets improve glucose tolerance. Glucose fluctuations were significantly greater during ingestion of diets containing corn syrup than during those containing sucrose. The percentage of dietary energy supplied as carbohydrate did not influence glucose fluctuations significantly.

Diets containing corn syrup were associated with significantly higher integrated concentrations of insulin than the sucrose diets. Insulin-integrated concentrations did not vary significantly with changes in the percentage of dietary carbohydrate. The insulin response to the glucose tolerance test did not vary with the source of carbohydrate and did not accurately reflect the 24-hour mean insulin concentrations.

We concluded that (1) a change in the percentage of energy supplied as carbohydrate does not significantly influence the concentration of either glucose or insulin in normal subjects; (2) concentrations of glucose throughout the day are more stable when the dietary carbohydrate is sucrose than when it is corn syrup; (3) sucrose-containing diets require significantly lower insulin concentrations to maintain euglycemia than do corn syrup–containing diets; (4) glucose and insulin responses to an oral glucose tolerance test do not accurately reflect the 24-hour glucose and insulin concentrations obtained during ingestion of the test diets.

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