a1 Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7XH, UK
a2 Nutrition and Dietetic Research Group, Investigative Science, 6th Floor Commonwealth Building, Faculty of Medicine, Imperial College, Hammersmith Campus, DuCane Road, London W12 ONN, UK
Shiftworkers have a higher risk of CHD and type 2 diabetes. They consume a large proportion of their daily energy and carbohydrate intake in the late evening or night-time, a factor which could be linked to their increase in disease risk. We compared the metabolic effects of varying both dietary glycaemic index (GI) and the time at which most daily energy intake was consumed. We hypothesised that glucose control would be optimal with a low-GI diet, consumed predominantly early in the day. A total of six healthy lean volunteers consumed isoenergetic meals on four occasions, comprising either high- or low-GI foods, with 60 % energy consumed predominantly early (breakfast) or late (supper). Interstitial glucose was measured continuously for 20 h. Insulin, TAG and non-esterified fatty acids were measured for 2 h following every meal. Highest glucose values were observed when large 5021 kJ (1200 kcal) high-GI suppers were consumed. Glucose levels were also significantly higher in predominantly late high- v. low-GI meals (P < 0·01). Using an estimate of postprandial insulin sensitivity throughout the day, we demonstrate that this follows the same trend, with insulin sensitivity being significantly worse in high energy consumed in the evening meal pattern. Both meal timing and GI affected glucose tolerance and insulin secretion. Avoidance of large, high-GI meals in the evening may be particularly beneficial in improving postprandial glucose profiles and may play a role in reducing the risk of type 2 diabetes; however, longer-term studies are needed to confirm this.
(Received July 11 2011)
(Revised October 24 2011)
(Accepted October 29 2011)
(Online publication December 16 2011)
Abbreviations: GI, glycaemic index; HGI-am, high glycaemic index, with majority of energy load consumed in the morning; HGI-pm, high glycaemic index, with majority of energy load consumed in the evening; LGI-am, low glycaemic index, with majority of energy load consumed in the morning; LGI-pm, low glycaemic index, with majority of energy load consumed in the evening