The GI provides a good summary of postprandial glycemia. It predicts the peak (or near peak) response, the maximum glucose fluctuation, and other attributes of the response curve.

Background: Low glycemic index (GI) carbohydrates have been linked to increased satiety. The drive to eat may be mediated by postprandial changes in glucose, insulin and gut peptides. Objective: To investigate the effect of a low and a high GI diet on day-long (10 h) blood concentrations of glucose, insulin, cholecystokinin (CCK) and ghrelin (GHR). Design: Subjects (n ¼ 12) consumed a high and a low GI diet in a randomized, crossover design, consisting of four meals that were matched for macronutrients and fibre, and differed only in carbohydrate quality (GI). Blood was sampled every 30-60 min and assayed for glucose, insulin, CCK and GHR. Results: The high GI diet resulted in significantly higher glucose and insulin mean incremental areas under the curve (IAUC, P ¼ 0.027 and P ¼ 0.001 respectively). CCK concentration was 59% higher during the first 7 h of the low GI diet (394 ± 95 pmol/ l min) vs the high GI diet (163 ± 38 pmol/l min, P ¼ 0.046), but there was no difference over 10 h (P ¼ 0.224). GHR concentration was inversely correlated with insulin concentration (Pearson correlation À0.48, P ¼ 0.007), but did not differ significantly between the low and high GI diets. Conclusions: Mixed meals of lower GI are associated with lower day-long concentrations of glucose and insulin, and higher CCK after breakfast, morning tea and lunch. This metabolic profile could mediate differences in satiety and hunger seen in some, but not all, studies.

Acne vulgaris may be improved by dietary factors that increase insulin sensitivity. We hypothesized that a low-glycemic index diet would improve facial acne severity and insulin sensitivity. Fifty-eight adolescent males (mean age ± standard deviation 16.5 ± 1.0 y and body mass index 23.1 ± 3.5 kg/m2) were alternately allocated to high or low glycemic index diets. Severity of inflammatory lesions on the face, insulin sensitivity (homeostasis modeling assessment of insulin resistance), androgens and insulin-like growth factor-1 and its binding proteins were assessed at baseline and at eight weeks, a period corresponding to the school term. Forty-three subjects (n = 23 low glycemic index and n = 20 high glycemic index) completed the study. Diets differed significantly in glycemic index (mean ± standard error of the mean, low glycemic index 51 ± 1 vs. high glycemic index 61 ± 2, p = 0.0002), but not in macronutrient distribution or fiber content. Facial acne improved on both diets (low glycemic index −26 ± 6%, p = 0.0004 and high glycemic index −16 ± 7%, p = 0.01), but differences between diets did not reach significance. Change in insulin sensitivity was not different between diets (low glycemic index 0.2 ± 0.1 and high glycemic index 0.1 ± 0.1, p = 0.60) and did not correlate with change in acne severity (Pearson correlation r = −0.196, p = 0.244). Longer time frames, greater reductions in glycemic load or/and weight loss may be necessary to detect improvements in acne among adolescent boys.

Intramyocellular lipid (IMCL) and plasma NEFA are important skeletal muscle fuel sources. By raising blood insulin concentrations, carbohydrate ingestion inhibits lypolysis and reduces circulating NEFA. We hypothesised that differences in the postprandial glycaemic and insulin response to carbohydrates (i.e. glycaemic index; GI) could alter NEFA availability and IMCL use during subsequent exercise. Endurance-trained individuals (n 7) cycled for 90 min at 70 % V O 2peak and then consumed either high GI (HGI) or low GI (LGI) meals over the following 12 h. The following day after an overnight fast, the 90 min cycle was repeated. IMCL content of the vastus lateralis was quantified using magnetic resonance spectroscopy before and after exercise. Blood samples were collected at 15 min intervals throughout exercise and analysed for NEFA, glycerol, glucose, insulin, and lactate. Substrate oxidation was calculated from expired air samples. The 90 min cycle resulted in .2-fold greater reduction in IMCL in the HGI trial (3·5 (SEM 1·0) mM/kg wet weight) than the LGI trial (1·6 (SEM 0·3) mM/kg wet weight, P, 0·05). During exercise, NEFA availability was reduced in the HGI trial compared to the LGI trial (area under curve 2·36 (SEM 0·14) mEq/l per h v. 3·14 (SEM 0·28) mEq/l per h, P,0·05 respectively). No other differences were significant. The findings suggest that HGI carbohydrates reduce NEFA availability during exercise and increase reliance on IMCL as a substrate source during moderate intensity exercise.Glycaemic index: Intramyocellular lipid: Magnetic resonance spectroscopy: Exercise: Skeletal muscle During moderate intensity exercise, the energy for ATP homeostasis in skeletal muscle is primarily obtained from the oxidation of glycogen and lipid. Glycogen plays a pivotal role in producing energy and preventing the development of muscle fatigue in submaximal exercise 1 -4 . Intramuscular lipid levels are also readily oxidised during prolonged exercise 5 -7 and are elevated in endurance-trained individuals 8 . The rate of substrate oxidation, whether glycogen or lipid, is influenced by both existing pre-exercise substrate within the muscle 9 , and circulating substrate availability during exercise 10 -13 . Although considerable work has been undertaken on optimising glycogen storage with diet, less is known about the relative influence of diet upon both glycogen and lipid oxidation.High levels of carbohydrate intake have been shown to improve glycogen repletion after exercise 14,15 . An early study also reported that consuming carbohydrates which are rapidly absorbed into the circulatory system, termed high glycaemic index (HGI) carbohydrates, optimised the storage of plasma glucose as skeletal muscle glycogen following glycogen-depleting exercise 16 . It has also been reported that the postprandial hyperinsulinaemia accompanying high carbohydrate intake reduces the rate of fat oxidation 17 -19 , increasing reliance upon glycogen oxidation during exercise. Although high postprandial levels of insulin may increas...