bservational studies show an inverse relationship between fibre intake and obesity. One line of reasoning suggests that fibre is protective of obesity because it can decrease the glycaemic effect of foods. Consumption of low fibre refined carbohydrates causers elevated postprandial plasma insulin and glucose concentrations compared to whole grain foods. Studies have shown that incorporating fibre into the diet either as supplements or as whole grain cereals, lowers postprandial insulin levels and improves glycaemic control. The Western diet is devoid of meaningful levels of fibre and this may be a major cause of weight gain in those who regularly consume it. Long-term consumption of refined carbohydrates causes metabolic dysfunction that eventually leads to the development of insulin resistance and metabolic syndrome, with associated weight gain. However, in the short-term low fibre refined carbohydrate diets may increase appetite when compared to high fibre whole grains.
Researchers1 have investigated the appetite suppressing effects of dietary fibre by comparing high and low fibre breakfast cereals. For breakfast 14 subjects consumed one of five cereals with milk and orange juice, and at midday they were presented with a buffet for ad libitum consumption. The cereals contained 0, 11, 18, 35 and 39 g of fibre per 100 g. When the authors analysed the results they found that there was an inverse association between the amount of fibre eaten at breakfast and the amount the subject ate at the buffet lunch, suggesting that fibre had decreased the appetite of the subjects. In a follow-up study, the subjects ate either a very high fibre cereal (0 g fibre per 100 g) or a very low fibre cereal (39 g fibre per 100 g) followed a few ours later by lunch. Those subjects who ate the very high fibre cereal consumed fewer calories at lunch compared to those who ate the very low fibre cereal.
The amount of microbial fermentation in the colon was assessed in the subjects after the breakfast cereals using a hydrogen breath test. Those subjects consuming the most fibre had the greatest fermentation in their colon. This suggests that the fibre was being converted in the colon to short-chain fatty acids, such as propionate, butyrate and acetate. These short-chain fatty acids are known to be absorbed, and then enter the liver for processing. Evidence suggests that short-chain fatty acids from colonic fermentation of fibre have a number of metabolic effects in humans, one of which is the ability to provide a source of energy. This may explain the appetite suppressing effects of dietary fibre and may explain the inverse association between fibre intake and appetite. Therefore fibre may regulate short-term appetite through a combination of improved glycaemic control and the production of short-chain fatty acids.
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