The metabolizable energy (ME) of two diets that differed in their content of dietary fiber (DF) from cereal products was measured in balance experiments in six human subjects. DF intake was 19.7 g/d with the low fiber diet and 48.3 g/d with the high fiber diet. Daily gross energy intakes were 2114 kcal (8845 kJ) and 2341 kcal (9795 kJ)/d with the low and the high fiber diets, respectively. DF contributed 83 kcal (347 kJ) and 203 kcal (849 kJ) to daily gross energy intake with the low and the high fiber diets, respectively, when heat of combustion of DF of 4.2 kcal (17.6 kJ)/g was assumed. Increasing the intake of DF resulted in an increase in stool weight and a greater fecal energy loss. Total energy losses were 253 kcal (1056 kJ) and 409 kcal (1711 kJ)/d with the low and the high fiber diets, respectively. ME provided by the low and the high fiber diet were 1861 kcal (7786 kJ) and 1932 kcal (8083 kJ)/d. The total increase in energy losses due to the increase in DF consumption exceeded the gross energy provided by additional DF. Compared with the low fiber diet, ME provided by protein and fat was decreased during the high fiber diet. Calculation of the apparent digestibility of DF indicated that fiber may have provided ME in the form of short-chain fatty acids during the low as well as during the high fiber intake. However, estimation of the amount of fecal gross energy indicated that available components of the diet, such as starch, must have been utilized incompletely during both experimental periods.

The present study investigated whether the extent of fermentation of NSP in human subjects could be predicted by an in vitro batch system. Fibre sources studied were five mixed diets containing different amounts and types of fibre and three single fibre sources (citrus fibre concentrate, coarse and fine wholemeal rye bread). Fermentation in human subjects was determined in balance experiments in women who were also donors of the faecal inocula. In vitro fermentations were performed with fibre residues prepared from duplicates of the fibrecontaining foods consumed during the balance trials. Fermentation of total NSP in vivo was between 65 . 8 and 88 . 6 % for the mixed diets and 54 . 4, 58 . 0 and 96 . 9 % for the coarse and fine wholemeal rye breads and the citrus fibre concentrate respectively. For the mixed diets and the citrus fibre concentrate, mean differences between the extent of NSP degradation after 24 h in vitro incubation and that in vivo were between −0 . 7 and 5 . 0 %. Differences were significant for one diet (P < 0 . 05). For the wholemeal rye breads, the fermentation in vitro exceeded that in vivo significantly, but the magnitude of the difference in each case was small and without physiological importance. Particle size of breads had no influence on the extent of NSP degradation. These results indicate that the in vitro batch system used could provide quantitative data on the fermentation in vivo of NSP in mixed diets and some single fibre sources. An in vitro incubation time of 24 h was sufficient to mimic the NSP degradation in vivo.Fermentation: Non-starch polysaccharides: In vitro batch system NSP are the predominant components of dietary fibre (DF). Their susceptibility to bacterial fermentation is of major significance for the actions of DF in the large intestine. Fermentation of NSP affects their structural properties and water-holding capacity and thereby their effect on stool weight. Fibres that are extensively degraded have a lower faecal bulking capacity than more resistant types of fibre (Stephen & Cummings, 1980). This is especially the case if the fermentation is rapid and occurs mainly in the proximal colon ). The short-chain fatty acids (SCFA) acetate, propionate and butyrate formed from bacterial NSP breakdown are efficiently absorbed. Besides their contribution to the body's energy supply (McNeil, 1984), they have specific metabolic functions. Butyrate, for example, is the preferred fuel of colonic epithelial cells (Roediger, 1982) and is thought to contribute to the protective role of fibre against large-bowel cancer (Bingham, 1990).Fermentability of NSP and production of SCFA can be studied rather easily with in vitro batch systems utilizing faecal bacteria. These in vitro systems have several advantages over time-consuming and expensive human fermentation studies. In vitro systems are inexpensive, different NSP sources can be fermented at the same time and they can be used for screening of new fibre sources not yet permitted for human consumption. In vitro studies using rat f...

The effects of a low-phytate barley-fiber concentrate on calcium, magnesium, and zinc balances and on apparent iron absorption were measured by balance experiments. During the three experimental periods of 22 d each, all subjects consumed the basal diet alone, the basal diet with 15 g barley fiber (high-fiber, high-protein diet), and a modified basal diet containing less protein with 15 g barley fiber (high-fiber, low-protein diet), respectively. The mean daily intake of the cations was 24.4, 25.4, and 22.9 mmol Ca; 10.4, 10.1, and 10.0 mmol Mg; 165.2, 166.8, and 119.3 mumol Zn; and 154.0, 186.2, and 154.0 mumol Fe, respectively. Mean balances were 0.2, 1.9, and -0.8 mmol Ca; 0.3, -0.2; and -0.5 mmol Mg; 3.0, -4.6, and -18.4 mumol Zn. The mean apparent iron absorption was 16.1, 5.4, and -23.2 mumol when these three diets, respectively, were consumed.

The metabolizable energy (ME) of two diets, which differed in their content of dietary fiber mainly from fruits and vegetables, was determined in balance experiments in eight young women. The ME of the diets was also calculated by the specific factors of Merrill and Watt, by the general factors of Atwater, by the modification of Atwater's procedure used in the Federal Republic of Germany, and also by the equations of Southgate, of Miller and Payne, and of Miller and Judd. The daily intake of fruits, vegetables and potatoes was 505 and 1235 g with the low and the high fiber diets, respectively. Normally, young German women consume only 350 g of these foods each day. Dietary fiber intake was 18.8 g/d with the low fiber diet and 52.0 g/d with the high fiber diet. Daily gross energy intakes were 8540 and 8916 kJ (2041 and 2131 kcal) with the low and the high fiber diets, respectively. The apparent digestibility of energy was lower when the high fiber diet was consumed. Measured ME was 7665 and 7544 kJ/d (1831 and 1802 kcal/d) with the low and high fiber diets, respectively. It was calculated that fiber from fruits and vegetables contributed to ME about 3 kJ (0.7 kcal) per gram of fiber. On the average, the ME of the low fiber diet could be predicted by all calculation procedures except the formula of Miller and Judd. The ME of the high fiber diet could best be predicted by the specific factors of Merrill and Watt and by the Southgate formula.

The apparent digestibility of energy, protein, fat and non-starch polysaccharides (NSP) of low and high dietary fibre (DF) mixed diets were studied in three series of experiments with man and the rat. Low DF diets were used as control diets in each experimental series and the DF level was increased by adding fruits and vegetables (Study 1), citrus fibre concentrate (Study 2) and insoluble barley fibre (Study 3). In Study 3 the high DF diet was fed at two protein levels. There was in most cases good agreement between the digestibility of energy between man and the rat, with the digestibility of energy of the low DF control diets of 0.9414950 in man compared with 0.9334952 in the rat and of the high D F diets of 0,8974931 in man and 0.865-0.920 in the rat. The biggest difference in digestible energy between the two species was found for the diet enriched with fruits and vegetables (0.032 absolute units) and citrus fibre concentrate (0.025 absolute units). Apparent digestibility of protein was slightly lower in man than in the rat for all diets in Studies 1 and 2. In Study 3, however, apparent digestibility of protein was consistently lower in man than in the rat with differences in absolute digestibilities between the two species varying from 0.023 (high DF/high protein) to 0.071 (high DF/low protein). The digestibility of fat was the same in man and in the rat in all but the high DF diet of Study 2. The rat appears to have a lower capacity to digest fibre polysaccharides than man and the digestibility of NSP was consistently lower in the rat than in man. The biggest difference between the two species was found for the diets in Study 2 where the digestibility of N S P in man was measured to be 0.774-0.885 compared with only 0.5014517 in the rat. For the other diets the differences in NSP digestibility were 0.0774137 absolute units. In spite of some differences between man and the rat in their ability to digest nutrients the various diets are ranked in the same order by the two species. Digestibility: Dietary fibre: Man: RatThe need for appropriate animal models when studying questions in human nutrition is very great because under many experimental conditions and situations it is difficult or impossible to use human subjects. Furthermore, studies with humans are generally complicated, time-consuming and expensive.The rat is the most frequently used animal model for studying digestibility in humans and much valuable information is produced using the rat in such studies (Food and Agriculture Organization/World Health Organization (FAO/WHO), 1991). The great value of the rat model is the low cost associated with relatively simple research facilities and turnover. This allows the use of large numbers of animals and rapid production of results. One major advantage is that the rat is omnivorous, thus allowing studies on a wide variety of foods. This makes it possible to test a nutrient source as the sole dietary component and avoid Downloaded from https://www.cambridge.org/core.