Plain language summary
Previous studies have shown a difference between low glycaemic index (GI) and high GI energy restricted diets on mood and cognition. This randomised trial of 46 healthy overweight individuals aimed to assess the long-term effects of LG or HG energy restricted diet on mood and cognition function. Individuals were randomly assigned to a low GI or a high GI diet with caloric restriction for 12 months. The study did not observe any difference in cognitive function of individuals assigned to either the low GI or the high GI diet but it did show a beneficial effect of low GI diet on subclinical depression. The results of this small study were consistent with previous studies where low GI diets may be protective against negative mood change during weight loss whereas negative changes occur if a conventional high GI diet is consumed.
Abstract
Energy-restricted low glycemic load diets are being used increasingly for weight loss. However, the long-term effects of such regimens on mood and cognitive performance are not known. We assessed the effects of low glycemic load (LG) and high glycemic load (HG) energy-restricted diets on mood and cognitive performance during 6 months of a randomized controlled trial when all food was provided. Subjects were 42 healthy overweight adults (age 35+/-5 years; BMI 27.8+/-1.6 kg/m(2)) with a mean weight loss of 8.7+/-5.0% that did not differ significantly by diet randomization. Mood was assessed by using the Profile of Mood States (POMS) questionnaire. Cognitive performance was assessed by using computerized tests of simple reaction time, vigilance, learning, short-term memory and attention, and language-based logical reasoning. Worsening mood outcome over time was observed in the HG diet group compared to the LG for the depression subscale of POMS (p=0.009 after including hunger as a covariate). There was no significant change over time in any cognitive performance values. These findings suggest a negative effect of an HG weight loss diet on sub-clinical depression but, in contrast to a previous suggestion, provide no support for differential effects of LG versus HD diets on cognitive performance.
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