The effects of dietary fibre on weight control can be summarized as follows: Few controlled clinical studies have been carried out showing that supplementation with dietary fibre improves weight loss. In one study, patients were asked to maintain their dietary habits, while receiving 10 g guar gum twice daily for 8 weeks; average weight fell from 95.6 to 91.3 kg, but this was difficult to evaluate, since no control group was included (33). In further studies patients were given a reduced diet of 1000kcal/day, which in one group was supplemented with 24 g of fibre as oat bran biscuit, for 8 weeks (34). Weight loss in the fibre group was reported as high as 5.1 + 1.7 kg/week, compared with 3.8 + 1.8 kg in the control group. This study was, however, not blind, as the authors themselves also point out.
A few studies with adequate designs have been published that demonstrate that dietary fibre supplementation improves weight loss. Tuomilehto et al. (35) demonstrated that in a 16-week study period 15 g of guar gum daily resulted in a signifi cant weight loss compared with placebo, in normal weight subjects. Walsh et al. (36) treated 20 obese women with 3 g of purified glucomannan or placebo for 8 weeks. Patients on fibre lost a mean of 2.5 kg, whereas in the placebo group surprisingly a weight increase of 0.7 kg was seen during the corresponding time.
The most systematic approach to evaluating the role of dietary fibre supplementation on weight loss and weight maintenance seems to be the data summarized by Ryttig et al. (Table 30.5). In these studies, tablets consisting of combinations of 10-20% soluble (citrus) and 80-90% insoluble (grain) fibres were used (37). The studies were double-blind, randomized and placebo-controlled. A 1600 kcal diet was given for 12 weeks and this design resulted in similar weight losses in both groups. As indicated in Table 30.5, the other six Ryttig studies demonstrated that fibre supplementation significantly improved weight loss compared with placebo. These studies comprised 45 to 97 patients, who were mildly to moderately obese. The fibre supplementation was up to 7 g/day, the hypocaloric diets up to about 1800kcal/day, the treatment period ranging from 8 to 52 weeks. Overall, fibre improved the weight loss obtained by the diet by about 40%. In these studies hunger feelings in fibre groups decreased with time, in contrast to ratings in controls, and the number of withdrawals was significantly lower in fibre-treated patients than in controls.
These studies were performed with fibre-supplemented diets. No studies performed with diets varying in fibre content have tested the effect of dietary manipulation with fibre. The overall effects of dietary fibre on obesity treatment are summarized in Table 30.6.
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