Fiber, dietary hypothesis

The data on absorption efficiency of Mn are by no means consistent, but efficiency is probably in the range of one to three percent depending on the type of diet and on the presence or absence of dietary Mn antagonists (eg., ash or fiber). This range of absorption efficiencies in the chick is not greatly different from estimates of one to four percent made in mammals (28-29). Thus, the chick s high Mn requirement relative to mammals is probably not totally a result of inefficient Mn absorption. Instead, avians may experience a more rapid turnover of stored Mn than mammals, although more definitive data are needed to verify this hypothesis. 

Our own interest in dietary fiber was stimulated by the originally suggested mechanism by which primitive diets affect carbohydrate metabolism. According to the hypothesis, the... 

Dietary fiber might be a factor protecting against atherosclerotic disease ( 1.). This hypothesis is based on epidemiological data linking a large number of "Western" diseases with a low intake of dietary fiber (.1) 8° experimental support,... 

Experiments with chemically induced colon cancer in the rat have partially, but not consistently, supported the dietary fiber hypothesis (12). Thus, Bauer et al. (13,14) recently reported that both high- and low-methoxylated pectin (6.5 or 5% in a diet containing 20% casein, 20% fat and no other dietary fiber) given during induction of colon cancer with subcutaneous 1.2-dimethyl— hydrazine, enhanced the yield of tumors. Guar gum, 5%, also tended to increase the tumor yield, although not significantly compared with controls on a virtually fiber-free diet. Others(15) however reported a protective effect of 15% pectin. 

Considerably more data is available with respect to the relationship between dietary fiber intake and fecal bile acid excretion. The basic hypothesis of the role of dietary fiber in ameliorating gastrointestinal disease[41] suggests that increased fiber intake bulks the stool and dilutes the concentration of luminal contents, including bile acids. In practice depending upon the fiber supplement a range of effects on stool bulk and fecal bile acid concentrations are observed. 

The beneficial effects of dietary fiber on the alimentary tract were emphasized by another of the founders of the dietary fiber hypothesis, Denis Bur-kitt, who based his arguments largely on the concept of fecal bulk, developed as a result of field... 

It can be hypothesized that a reduction in the general and postprandial glycemic and insulinemic response may delay the development of insulin resistance and thus the development of diabetes (NIDDM) although there is very little direct evidence to support this hypothesis. However, diets high in both carbohydrate and dietary fiber have been reported to improve insulin sensitivity. Much of the research in this area has studied the effect of dietary fiber on the management rather than the prevention or etiology of diabetes. 

---