Effects of short-term low- and high-carbohydrate diets on postprandial metabolism in non-diabetic and diabetic subjects.

BACKGROUND AND AIM

Low-fat high-carbohydrate diets raise plasma triacylglycerol (TG) concentrations. To test whether the nature of the carbohydrate affects metabolic responses, we conducted a randomized cross-over study using a short-term, intensive dietary modification.

METHODS AND RESULTS

Eight non-diabetic subjects and four subjects with diet-controlled type 2 diabetes participated. They followed three isoenergetic diets, each for 3 days: high-fat (50% energy from fat), high-starch and high-sugar (each 70% energy from carbohydrate). Normal foods were provided. We measured plasma TG and glucose concentrations, fasting and after a standard test meal, on day 4 following each dietary period. Fasting TG concentrations were greatest following the high-sugar diet (mean+/-SEM for all subjects 1900+/-420micromol/l) and lowest following high-fat (1010+/-130micromol/l) (P=0.001); high-starch (mean 1500+/-310) and high-fat did not differ significantly (P=0.06). There was a greater effect in the diabetic subjects (diet x diabetes status interaction, P=0.008). Postprandial TG concentrations were similarly affected by prior diet (P<0.001) with each diet different from the others (P<or=0.01). The elevation of fasting TG on the high-sugar versus high-fat diet was strongly related to the average fasting TG concentration (P=0.01 across both diabetic and non-diabetic subjects). Fasting glucose concentrations were not affected by prior diet but postprandial glucose concentrations were (P=0.018), with significantly higher values after the high-fat than the high-sugar diet (P=0.03).

CONCLUSIONS

The short-term TG-raising effect of a very low-fat diet is dependent upon the nature of the carbohydrate, with a greater effect of a sugar-rich than a complex-carbohydrate-rich diet.