Intake of rye fibre increases the excretion of energy. This may help to prevent the development of obesity.

High fibre diets have several positive effects on human health. One of these is helping to control body weight. The most important mechanism is undoubtedly that whole grain food may increase the bulk of the food and probably long-term satiety (Koh-Banerjee and Rimm 2003; Liu et al. 2003). The effects on satiety are not scientifically proven but they can be tested individually by trial and error. The soluble fibre in rye is expected to increase the viscosity of food in the stomach, and thus delay the evacuation of stomach contents into the small intestine. This prolonged stay of food in the stomach increases the replete feeling, and thus helps in dieting (Hagander et al. 1987).

A second and possibly less-important but significant mechanism is that some factor in the whole grain fibre complex may decrease the availability of energy from a diet. There is an increase in the excretion of nitrogen, fat and energy from the small intestine in individuals eating a whole grain rye diet and this is highly correlated with the dry matter of the small intestinal content (Zhang et. al. 1994). In a follow-up experiment, they have confirmed the first results and further characterized the components of the excreted materials. In this study on ileostomy subjects the intake of high-fibre rye bran bread or wheat bread during different dietary regimes (nibbling - 7 meals/day, or gorging - 3 meals/day) was investigated with an emphasis on the excretion of energy and nutrients. The intake of rye bran bread increased the excretion of all nutrients (fat, protein and carbohydrates) and energy in all individuals. The excretion of nutrients and energy did not differ between the two eating regimes. During the high-fibre period the energy excretion was almost as much as twice the amount (2400 kJ/day) compared to the excretion during the wheat bread period (1400 kJ/day) as measured using a bomb calorimeter.

On the other hand, even though human enzymes cannot break down dietary fibre, part of the energy in dietary fibre can become available for humans following the microbial breakdown of the dietary fibre polysaccharides in the colon and the formation of short-chain fatty acids. Therefore, the energy obtained from dietary fibre depends largely on the extent of fibre fermentation (Slavin 2003). The net effect of these processes of energy utilization has, however, not yet been clarified, but experiments are under way to study what is happening in the large intestine.

In animal experiments it has also been found that exogenous fibre-degrading enzymes added to the rye diet increase the amount of energy received from rye (Petterson et al. 1994, Boros 1995). From this it could be assumed that the fibre in rye restricts the uptake of energy from the small intestine.
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