Influence of dietary fiber from vegetables and fruits, bran or citrus pectin on serum lipids, fecal lipids, and colonic function

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Abstract
The effects of dietary fiber from different sources on cholesterol metabolism and colonic function were investigated in a group of 62 young healthy volunteers under strict dietary control. All foodstuffs except for 100 kcal/day were supplied, taking into account each subject's energy needs. The subjects consumed a relatively low-fiber diet for 2.5 weeks, after which period they were divided into four groups. For the next 5 weeks one group continued on the low-fiber diet, a second group received a high-fiber diet rich in vegetables and fruits, while the diets of the third and fourth group were supplemented with citrus pectin and wheat bran, respectively. These four groups consumed on average 18, 43, 28, and 37 g dietary fiber per day, respectively. Differences in consumption of type and amount of fat, cholesterol, protein, and carbohydrates between the groups were negligible, as ascertained both by 5-day food records and by analysis of duplicate portions. The concentration of serum total cholesterol decreased in those subjects on the diet containing citrus pectin and also in those on the diet containing vegetables and fruits, by 0.34 and 0.17 mmole/liter (13 and 7 mg/dl), respectively. The addition of bran, however, caused a statistically significant increase of 0.34 mmole/liter (13 mg/dl). The amount and type of dietary fiber had no significant effect on the concentration of serum high-density lipoprotein-cholesterol. The effects on serum total cholesterol could be explained only to a small extent by changes in the excretion of fecal steroids. The high-fiber diet with vegetables and fruits as well as the diet with bran shortened the intestinal transit time by 13 and 19 hr, respectively, and enhanced feces production by 49 and 77 g wet weight per 24 hr, respectively. Pectin had no effect on colonic functions. After 5 weeks no deleterious effect on Mg2+ or Ca2+ absorption was observed. The higher intake of potassium from the diet containing vegetables and fruits was not accompanied by a lowering of blood pressure. It is concluded that—at least in short-term controlled experiments—fiber components from vegetables and fruits, in contrast with bran, have a small favorable effect on the concentration of serum cholesterol. Both a vegetables/fruits diet and a bran diet may improve colonic functions.

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