Fibre has some interesting nutritional properties that may make it useful in the control of body weight. Removing fibre from the diet, as occurs when refined and processed starches are consumed, may therefore have detrimental effects. In fact, the typical Western diet, characterised by such processed and refined starches, has been shown to increase the risk of obesity, the metabolic syndrome, type 2 diabetes and insulin resistance when regularly consumed. Fibre likely has two main effects with regard weight control, and these centre on its effects on postprandial glycaemia. Firstly, soluble fibre has a gel-like consistency when exposed to the aqueous environment of the gut and this inhibits the digestion rate of starch and the absorption rate of the subsequent glucose. This flattens the blood sugar curve postprandially which may have beneficial appetite regulatory effects. Insoluble fibre adds bulk to the food, and this limits the amount of food that can be consumed and also slows its consumption.
Supplements of fibre may therefore be beneficial to weight loss. For example in one study1, researchers investigated the effects of one week of supplementation with guar gum in obese women following a period of weight loss. In one experiment, supplementation with 40 grams of fibre decreased energy intake from 1601 to 1290 kcal without a change in hunger or satiety. In another experiment, 40 grams of fibre significantly decreased hunger scores in subjects consuming 956 kcal per day following supplementation with 40 grams of fibre. At higher energy intakes of 1434 kcal, no changes to appetite were observed. Therefore guar gum fibre may decrease the energy intake of subjects consuming higher energy intakes and decrease the hunger of those consuming lower energy intakes. The effects of water soluble fibre such as guar gum on appetite and energy intake may explain the weight loss effects of whole grain traditional diets that contain foods naturally rich in their original fibre, including gums.
However, while studies have investigated the weight loss and postprandial glycaemic effects of supplemental fibre, the results have been inconsistent. Some have interpreted this as a lack of efficacy for fibre at controlling blood sugar and body weight. However, supplemental fibre is not in the same form as fibre found in foods, because supplemental fibre is processed. Whole foods tend to contain their fibre and starch as structurally linked components. Fibre in plant material tends to surround or be intertwined with starch. This relates to the location of the fibre in the cell walls of the plants. Supplemental fibre can be present in the gut along with starch, but it does not surround it and is not structurally continuous with it. Therefore the postprandial effects and by extrapolation the weight maintenance effects of supplemental fibre may not be as apparent as fibre in whole foods. The fibre in whole foods therefore tend to form a stronger and more consistent physical barrier to digestion when compared to supplemental fibre.
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