We have investigated the functional properties of food ingredients and nutrients in the intestine with special reference to anti-disease functions. This review article introduces our nutritional studies of protective factors such as resistant protein and vitamin B₆ through their effects in the intestine. (1) We have obtained evidence that the hypocholesterolemic activity of buckwheat protein is at least partially due to its lower digestibility by intestinal proteases. On the basis of these studies, we proposed the novel concept of “resistant protein”. This issue has been investigated in studies using a silk protein, sericin, as a resistant protein. Furthermore, we have successfully developed a method for production of the undigestive fraction from sake cake. (2) We have demonstrated a strong anti-tumor effect of dietary vitamin B₆ in the colon of mice, and studied the molecular mechanisms involved. According to several recent studies, the anti-tumor effect of vitamin B₆ appears to be more profound in the colon than in other organs. Therefore, vitamin B₆ is now considered to be a protective food factor against colon cancer.

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[Objectives] In a randomized placebo-controlled double-blind trial, we investigated the safety of long-term intake of chocolate containing plant sterol (1,200 mg/day) and its effect on serum cholesterol in subjects with borderline-high cholesterol or mild hypercholesterolemia. [Methods] Ninety-nine subjects (53 males and 46 females) were randomly assigned to two treatment groups: a placebo group given placebo chocolate, and a test group given chocolate containing plant sterol at 1,200 mg/day for 12 weeks. Every 4 weeks, fasting blood and urine samples were taken and several serum and urinary parameters were measured, including serum lipids. Adverse physical effects as well as signs and symptoms were also examined. [Results] In the test group, serum total cholesterol and LDL-cholesterol levels were significantly reduced at 4, 8, and 12 weeks after the start of taking chocolate containing plant sterol. In comparison with the placebo group, the test group showed significantly lower serum total cholesterol and LDL-cholesterol levels at 4 and 8 weeks. Results of laboratory examinations for adverse effects were all within the normal ranges. No adverse physical effects were found, nor were any signs or symptoms of adverse events observed during the experimental period in the test group. [Conclusions] Long-term intake of chocolate containing plant sterol reduces the serum total and LDL-cholesterol levels, and raises no safety concerns in subjects with borderline-high cholesterol or mild hypercholesterolemia.

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The effect of fermented brown rice （FBR） containing high levels of nucleic acids on glycemic control was examined in rats. Male Wistar rats aged 9 weeks were used. Rats in a control group （BRC） were orally administered a solution containing 0.5 g of starch, 0.5 g of normal brown rice, and 4 mL of distilled water. Rats in the FBR group were administered a solution containing 0.5 g of starch, 0.5 g of fermented brown rice, and 4 mL of distilled water. Rats in a nucleic acid group （BRN） were administered a solution consisting of the starch mixture given to BRC group with an addition of nucleic acid containing DNA （0.003 g） and RNA （0.02 g） levels equivalent to those in FBR. The increases in the blood sugar and insulin levels in the FBR and BRN groups were significantly slower than in the BRC group. From these results, it is suggested that intake of fermented brown rice would minimize insulin secretion, thus attenuating any subsequent rise in the level of blood sugar.

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