Glucagon release following experimental diets in man: effects of soybean and casein enriched diets

Double-blind study of the addition of high-protein soya milkv. cows' milk to the diet of patients with severe hypercholesterolaemia and resistance to or intolerance of statins

Total substitution of soyabean protein for animal protein in the diet has been repeatedly shown to lower plasma cholesterol levels in hypercholesterolaemic individuals. A new, highly palatable, high-protein soya drink may allow replacement of a significant percentage of animal protein in the diet. The soya drink was given, within a crossover designv. a cows' milk preparation of similar composition and taste, to twenty-one severely hypercholesterolaemic patients (mean baseline plasma cholesterol 8·74 mmol/l) with a history of resistance to or intolerance of statin treatment. Each dietary supplement was given for 4 weeks, with a 4-week interval between treatments, Plasma lipid levels were monitored every 2 weeks during each dietary sequence. The concomitant dietary treatment, which had been followed for a long time by all patients, was carefully monitored throughout the study. The soya supplementation reduced plasma total cholesterol level by 6·5%, when given first, and by 7·4% when given after cows' milk. When given first, cows' milk resulted in a small, non-significant reduction of plasma cholesterol level (-3·9%), and when given after soya, it changed total plasma cholesterol to a minimal extent (-1·6%). Changes in total and LDL-cholesterol levels after 2 and 4 weeks of soyav. cows' milk treatment were, thus, respectively -6·1, -7·0 and -6·2, -7·8% (bothP< 0·05). These first data from a double-blind study confirm a significant cholesterol-lowering effect of soyabean protein, even when only partly replacing animal protein in the diet, in individuals with extreme plasma cholesterol elevations.

Hypocholesterolemic effect of soybean protein in rats and mice after peptic digestion

Analyses of gastrointestinal contents of rats fed soybean protein isolate and casein showed that soybean protein was readily digested in the stomach but migrated slowly in the small intestine. The soluble fraction of the stomach contents of rats fed soybean protein was separated by gel-filtration on Sephadex G25 into large and small molecular fractions, the latter was not found in rats fed casein. The formation of low-molecular-weight peptides was pH dependent, and analogous peptides were produced by pepsin in vitro not only from soybean protein but also from casein. In rats the peptic digest of soybean protein was found to be as hypocholesterolemic as intact soybean protein. Meanwhile, the cholesterol-lowering action of the large molecular fraction of the peptic digest tended to be greater than that of the small molecular fraction in mice. These observations suggest a significant role of peptic digestion in the cholesterol-lowering action of soybean protein.