Effect of konjac glucomannan on metabolic responses and appetite regulation in healthy adults

Awlya, Ohaad F (2022) Effect of konjac glucomannan on metabolic responses and appetite regulation in healthy adults. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Background: The rapid rise in the prevalence of obesity and type 2 diabetes (T2DM) has caused major health concerns worldwide. There is evidence that increased dietary fibre (DF) intake may protect against T2DM in adults. Furthermore, several studies underscore the effectiveness of viscous soluble DFs, including konjac glucomannan (KGM), in reducing body weight and blood cholesterol levels. Recent market research indicates the public awareness of the health benefits of DF and their preference for more convenient ways to improve DF consumption, including drinking fruit juice and smoothies. Nevertheless, there are concerns about their high sugar content, which may adversely affect metabolic homeostasis. Aim and objectives: This research aims to determine the impact of KGM preloading on the acute metabolic and appetite response to meal consumption. To achieve this goal, fives studies were conducted: A survey to elucidate the attitudes and perceptions of smoothie consumers in a university cohort; an experiment to examine the effect of KGM powder fortification on the rheological properties of commercial fruit smoothies; a survey of UK adults to explore their knowledge and awareness of DF consumption; a randomised crossover trial of healthy adults to evaluate the effectiveness of KGM capsule consumption at improving 2hr metabolic and appetite response to the ingestion of sugar-rich smoothies; a systematic review to assess the metabolic benefits of KGM capsules in healthy adults and adults with obesity and/or T2DM. Results: This research demonstrated that smoothie consumption was above the national UK average in the university cohort (92% vs 40%), and the majority of respondents described health benefits (65.5%) as their motivation for drinking smoothies but raised concerns about their sugar content (%). In addition, the majority of UK respondents to a second survey who consumed DF regularly believed that whole fruit contained more fibre and enhanced satiety and glycaemic control more so than fruit beverages. However, the addition of 0.5g,1g and 2g KGM powder to commercial fruit smoothies to improve their DF content, significantly increased viscosity (p<0.001), firmness (p<0.001), cohesiveness (p<0.001) and consistency (p<0.001) of smoothie samples, both immediately and after overnight storage causing rheological and sensory issues. To overcome this issue, KGM capsules were used in the subsequent human intervention. The consumption of KGM capsules before smoothie ingestion was associated with a significant (p=0.01) decrease in 2hr postprandial serum insulin concentration compared to 1g KGM and placebo. The effects of KGM on other measures (blood glucose and lipids, gastric emptying rate, subjective appetite, and circulating gut hormone (ghrelin, GLP-1, PYY and PP) concentrations were nonsignificant. In contrast to these non-significant acute effects, the systematic review found some evidence from RCTs on the effectiveness of KGM capsule supplementation (1g to 3g daily) for 4 to 8 weeks at reducing body weight, blood glucose, as well as total and LDL cholesterol in adults. Conclusion: This research demonstrated the awareness of health benefits of DF but limited knowledge about the fibre content of food products in the study population. It also showed that smoothies were popular, but there were concerns about their sugar content. However, the fortification of fruit smoothies with KGM powder was challenging and caused undesirable rheological changes in smoothies. Importantly, KGM capsule consumption had a modest effect of on acute (2hr) improvements in appetite and metabolic response to sugar-rich smoothie ingestion. Additionally, the systematic review found some evidence on the beneficial chronic effect of supplementation with KGM capsules on body weight, glycaemic control, and lipid profile (total and LDL cholesterol).