The role of fermentable carbohydrates on appetite regulation in humans

Abstract

This thesis investigates the ability of fermentable carbohydrates to stimulate anorectic gut hormones, which in turn reduce appetite and body weight. Fermentable carbohydrates have been shown to suppress food intake and body weight in rodents via the release of satiety hormones, glucagon-like peptide 1 (GLP-1) and peptide-YY (PYY). However, evidence of the effect of fermentable carbohydrates on modulating body weight in humans is contradictory. In this thesis, supplementing oligofructose over eight weeks has been shown to significantly reduce hunger and increase PYY secretion in overweight volunteers. However, there was no suppression on energy intake or body weight when compared with cellulose supplementation. Studies in rodents also suggested that reductions in food intake and body weight following intake of fermentable carbohydrates are associated with activation in the central nervous system. In contrast, oligofructose supplementation in this study had no significant effect on reducing activation in pre-selected brain reward regions in response to visual food cues, as measured by functional MRI. Surprisingly, the activation in these brain regions was reduced by cellulose intake. The negative findings from the oligofructose study may be due to insufficient concentrations of short chain fatty acids (SCFAs) in the colon. SCFAs, the fermentation end-products of ingested fermentable carbohydrates are thought to play a significant role in modifying energy homeostasis by stimulating PYY and GLP-1 from enteroendocrine L-cells in the colon. By applying a novel method of delivering propionate to the colon using a propionate carrier molecule (PCM), it has been shown that supplementation with PCM in healthy lean volunteers reduced hunger and energy intake in pilot studies via elevated PYY secretion. PCM also has a dose-dependent appetite inhibiting effect. The preliminary results in this thesis open up an interesting possibility of the development of the PCM as a dietary supplement to aid weight loss.