The digestion of four sources of resistant starch (RS) has been studied in twelve healthy volunteers who ate controlled diets for 15d periods. RS from potato, banana, wheat and maize (17-30g/d) was compared with a starch-free diet, a diet containing wheat starch that was fully digested in the small intestine, and with 18.4 g NSP from bran/d. RS increased stool wet weight by 1.6 g/d per g RS fed for potato, 1.7 for banana, 2.5 for wheat and 2.7 for maize, but this was significantly less than bran NSP at 4.9 g/g. RS was extensively digested in twenty-seven of thirty-four diet periods but five subjects were unable to break down one or two of the RS sources. Faecal N and energy excretion were increased. RS decreased NSP breakdown and RS, (resistant starch granules) tended to prolong transit time. All forms of RS increased faecal total short-chain fatty acid excretion. RS, (from potato and banana) gave greater proportions of acetate in faeces, and RS, (retrograded starch from wheat and maize) more propionate. We have concluded that RS, and RS, are broken down in the human gut, probably in the colon although in 26% of cases this breakdown was impaired. RS exerts mild laxative properties, predominantly through stimulation of biomass excretion but also through some sparing of NSP breakdown.

The digestibility of the starch in plant foods is highly variable, and is dependent on a number of factors, including the physical structure of both the starch and the food matrix. An in vifro technique has been developed to categorize starch in plant foods according to its likely rate and extent of digestion in the human small intestine. The in vitro method provides values for rapidly digestible starch, slowly digestible starch and resistant starch (RS). In the present study values for the RS content of foods, as measured by the analytical technique, were compared with the recovery of starch from these foods when fed to healthy ileostomates. Nine ileostomy subjects were given a plysaccharide-free diet with a breakfast supplement, on each of 2 d (two subjects) or 3 d (seven subjects), of biscuits made from wheat, potato or banana flours or from moist-heat-processed wheat or maize flours. RS intakes measured in vifro ranged from 8.5 to 15.0 g/d for the test biscuits, and mean starch recoveries in ileostomy effluent were 1004 (n 5, range 91-106) % of those values, but there was substantial variation between individuals. It is proposed that RS is defined as 'the sum of starch and starch-degradation products that, on average, reach the human large intestine'. The analytical method for the measurement of RS in vitro based on this definition is shown to provide an accurate prediction of the average amount of starch that is likely to escape complete digestion and absorption in the human small intestine.Resistant starch: lleostomy : Human small intestine In 1982 we reported that a fraction of starch in cooled, cooked foods was highly resistant to digestion by pancreatic amylase (EC 3.2.1 . 1) in vitro, and used the term resistant starch (RS) to describe this fraction (Englyst et al. 1982). Following a series of studies in healthy ileostomy subjects, who were used as a model for digestion in the small intestine (Englyst & Cummings, 1985, 1986, 1987, it became clear that this type of starch represented only a proportion of the starch that can resist digestion in the human small intestine. Starch that is trapped within whole plant cells or within the food matrix, and some starch granules that have not been fully gelatinized, are hydrolysed only very slowly by a-amylase and therefore may escape complete digestion in the small intestine. We therefore extended the term and modified the analytical procedure to include these sources, i.e. the definition of RS and its measurement in vitro were enlarged to include starch and starch-degradation products (Englyst & Cummings, 1987;Englyst & Kingman, 1990; Englyst et al. 1992a). The material included in the definition of RS reaches the human large intestine and thus becomes a substrate for microbial fermentation. The end-products are H, and CO,, CH, in about half the population, and short-chain fatty acids, which are absorbed and utilized. However, the energy yield to the body from this source is less than that provided if starch is digested and absorbed in the small intestine. The h...

When large amounts of sugars are included in the diets of humans and other animals, alterations in concentrations of plasma lipid constituents may be observed; usually elevation of triacylglycerol concentrations and sometimes elevation of low-density-lipoprotein cholesterol and depression of high-density-lipoprotein cholesterol. These effects are not seen with amounts of sugars typical of those in the Western diet, although more information is needed on postprandial triacylglycerol concentrations, which may be affected more readily than fasting concentrations. The elevation of triacylglycerol concentrations appears to reflect both increased hepatic very-low-density-lipoprotein triacylglycerol secretion and impaired clearance. Some people are more responsive to these effects of dietary sugars than are others. Perhaps surprisingly, in many studies people with diabetes mellitus, either insulin dependent or non-insulin dependent, seem to be protected from alterations in plasma lipid concentrations brought about by large amounts of dietary sugars.

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