Effect of glucose, sucrose and fructose on plasma glucose and insulin responses in normal humans: comparison with white bread

Objective: To determine the plasma glucose and insulin responses of various doses of glucose, sucrose, fructose and white bread in normal human subjects.

Design: Plasma glucose and insulin were measured before and at various times after 8 subjects ate 13 different test meals in randomized order on separate days after an overnight fast. Test meals consisted of 500 ml of tea or water to which was added either nothing, 25, 50, or 100 g of glucose or sucrose, 25 or 50 g fructose, 50 g glucose plus 50 g fructose, or a 25, 50 or 100 g carbohydrate portion of white bread. The glycaemic (GI) and insulinaemic index (II) values of the sugars were calculated by expressing the incremental areas under the plasma glucose and insulin curves (AUC) after glucose, sucrose and fructose as a percentage of the respective AUC after white bread containing the same amount of carbohydrate.

Setting: University teaching hospital clinical nutrition centre.

Subjects: Lean, normal subjects (4 male, 4 female) 21–33 y of age.

Results: Plasma insulin responses increased nearly linearly as carbohydrate intake increased from 0 to 100 g, but glycaemic responses increased by only 68% and 38% as carbohydrate intake increased from 25 to 50 g and 50 to 100 g, respectively. The GI and II values of glucose, 149±16 and 147±18, respectively, were significantly greater than those of bread (100; P<0.05), while the values for fructose, 16±4 and 22±3 were significantly less than those of bread (P<0.001). GI values did not differ significantly from II values.

Conclusions: It is concluded that, in normal subjects, as carbohydrate intake is increased from 0 to 100 g, plasma insulin responses increase at a greater rate than plasma glucose responses. The insulinaemic responses elicited by glucose, sucrose or fructose are similar to those that would be expected from a starchy food with the same glycaemic index.

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