Diurnal carbohydrate and fat distribution modulates glycaemic control in
rodents. In humans, the optimal timing of both macronutrients and its effects
on glycaemic control after prolonged consumption are not studied in detail. In
this cross-over trial, 29 non-obese men were randomized to two four-week
diets: (1) carbohydrate-rich meals until 13.30 and fat-rich meals between
16.30 and 22.00 (HC/HF) versus (2) inverse sequence of meals (HF/HC). After
each trial period two meal tolerance tests were performed, at 09.00 and 15.40,
respectively, according to the previous intervention. On the HF/HC diet,
whole-day glucose level was increased by 7.9% (p = 0.026) in subjects with
impaired fasting glucose and/or impaired glucose tolerance (IFG/IGT, n = 11),
and GLP-1 by 10.2% (p = 0.041) in normal glucose-tolerant subjects (NGT, n =
18). Diet effects on fasting GLP-1 (p = 0.009) and PYY (p = 0.034) levels were
observed in IFG/IGT, but not in NGT. Afternoon decline of glucose tolerance
was more pronounced in IFG/IGT and associated with a stronger decrease of
postprandial GLP-1 and PYY levels, but not with changes of cortisol rhythm. In
conclusion, the HF/HC diet shows an unfavourable effect on glycaemic control
in IFG/IGT, but not in NGT subjects. Consequently, large, carbohydrate-rich
dinners should be avoided, primarily by subjects with impaired glucose
metabolism