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Soy protein reduces inflammation in mice with colitis ulcerosa

Researchers hoped to find a protective effect of the probiotic bacteria Lactobacillus rhamnosus on ulcerative colitis in rats, but instead found that it was soy protein that was able to reduce inflammation.

Ulcerative colitis is an inflammatory bowel disease, which is an inflammatory condition of the colon and small intestine. Crohn's disease is also an inflammatory bowel disease. The inflammation of the lining of the digestive tract can lead to abdominal pain, diarrhoea, malnutrition and increased cancer risk. Millions of people in the Western world suffer from inflammatory bowel disease and its incidence is increasing yearly. The main risk factors for these diseases are smoking, oral contraceptives, diet, infections, appendectomy and hygiene during childhood.

Huanyi Jiang and co-workers at the Iowa State University explored the possible protective effects of soy protein, dairy proteins and Lactobacillus rhamnosus in a colitis mouse model. Previous studies have demonstrated that probiotic bacteria may have a beneficial effect on the intestinal mucosa. When mice are treated with dextran sodium sulphate, they develop similar symptoms as patients with ulcerative colitis. They fed mice with diets containing soy protein, whey protein or casein, with or without probiotic bacteria during 12 days. After seven days the mice were treated with dextran sodium sulphate and four days later their colon and cecum tissues were examined for signs of inflammation. The researchers found that only soy protein decreased inflammation parameters (such as colon shortening, mucin, tumor necrosis factor-alpha and trefoil factors), whereas whey protein and casein were not able to reduce the inflammatory impact of dextran sodium sulphate. Treatment with dextran sodium sulphate resulted in a significant higher mucin-1 increase in mice fed with casein or whey protein compared to mice fed with soy protein. Trefoil factor-3 was also more expressed in casein-fed mice compared with soy protein-fed mice. Mice fed with soy protein also showed lower expression of tumor necrosis factor-alpha in the colon and cecum than those fed with casein or whey protein.

The researchers wrote their most important finding was that soy protein significantly suppressed colon shortening and inflammatory response. But they were not able to identify the active components in soy protein. Often soy isoflavones are the bioactive component in many studies but for this experiment they used soy protein almost free from isoflavones. Lunasin, a bioactive soy peptide, was shown in other studies to reduce inflammation in macrophages. More studies are required to determine the potential mechanisms and bioactive components.

Source: Soy Protein Diet, but Not Lactobacillus rhamnosus GG, Decreases Mucin-1, Trefoil Factor-3, and Tumor Necrosis Factor-alpha in Colon of Dextran Sodium Sulfate-Treated C57BL/6 Mice. Journal of Nutrition. 2011 Jul;141(7):1239-46

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