Soy and Isoflavones:
Important Nutrition for Pets

The excellent nutrition delivered by soy is often overlooked when it comes to pet food diets. This “Nutrition Brief” will address this topic and discuss this ingredient’s many benefits. Nestlé Purina began research on the topic of soy isoflavones more than 5 years ago, and this newsletter will also present those positive findings.

Soy: A High Quality Ingredient

Soy is an excellent source of protein and carbohydrates. Whole soybeans contain 40% protein. And soybean germ meal, soybean meal, soy protein concentrate and soy protein isolate contain 42%, 48%, 65% and 90% protein, respectively. Soy is also rich in polyunsaturated fatty acids, very low in saturated fats and contains no cholesterol. In addition, it contains calcium, iron, zinc, phosphate and magnesium.

Soy as a Source of Highly Digestible Protein

The soy proteins in most commercial pet foods have digestibility values comparable, or superior to, protein from animal sources.^{1, 2} The apparent digestibility of protein from soy sources in diets of dogs has been variously reported as 71% to 90%.^{3, 4, 5, 6} Three isocaloric, isonitrogenous dry dog foods with primary protein sources of either beef and bone meal, soybean meal, or a combination of these two ingredients showed no difference in protein digestibility.¹ Other studies have shown that protein in soybean meal is at least as digestible as beef or poultry meals used in dog foods.^{2, 7} Based on this data, the bioavailability of amino acids from soybean protein is comparable to that of protein from animal sources.

Health Benefits of Soy

Many health benefits have been associated with regular consumption of soy products in humans. For instance, soy has been found to reduce the risk of cardiovascular disease and certain types of cancer (breast and prostate cancer in humans); relieve a number of problems in post menopausal women including hot flashes, osteoporosis, and decline in cognitive function; reduce cholesterol and triglycerides in plasma; improve symptoms of hypertension, and prevent abdominal fat
accumulation.^{8, 9, 10}

Soy has a long history of safe use in both humans and animals, including dogs and cats. On the following page, you'll discover how soy isoflavones can produce benefits for the health and well-being of pets.

The Beneficial Role of Isoflavones

Isoflavones are natural plant-based nutrients which have beneficial antioxidant properties. Isoflavones can be found naturally in plant sources such as chickpeas and green tea, but they are highest in soy products.

Soy isoflavones occur naturally in three different forms: daidzein, genistein, and glycitein. Soybean germ meal naturally contains high levels of daidzein and glycitein, the isoflavones found to be beneficial in healthy weight management in dogs.^{11, 12} A research study using ovariectomized rats found that the isoflavones daidzein and glycitein prevented increases in body weight and abdominal fat accumulation.¹³

The level of isoflavones in soybean germ meal is approximately four times the level in soy meal.^{14, 15}

Isoflavones and Obesity

Recognizing the safety of soy and the benefits observed in other species, Nestlé Purina began studying the benefits of soy isoflavones in dogs more than 5 years ago, using randomized, controlled
studies.^{11, 12, 15} Compared to the control diet, the isoflavone-containing diet was found to:

• Slow body fat accumulation and weight gain in overfed dogs.¹²
• Help reduce oxidative stress in overweight dogs, which may help reduce the risk of arthritis and diabetes.¹⁵
• Improve insulin clearance (the Purina Life Span Study showed that chronic high blood insulin was associated with certain chronic health problems, such as diabetes).¹⁵
• Increase energy metabolism (energy expenditure) in neutered male dogs.¹⁵

The safety of soy isoflavones was evaluated during long-term testing and no clinical evidence of adverse effects were observed, and the isoflavone-containing diet had no adverse effects on thyroid function, blood chemistry, or complete blood counts.

References
1. Huber, T.L., D. Laflamme, K.M. Comer, W.D. Anderson. 1994. Nutrient digestibility of dry dog foods containing plant and animal proteins. Canine Practice. 19:11
2. Zuo, Y., G.C. Fahey, Jr., N.R. Merchen, N.L. Bajjalieh. 1996. Digestion responses to low oligosaccharide soybean meal by ileally-cannulated dogs. J. Anim. Sci. 74:2441.
3. Kendall, P.T., D.W. Holme. 1982. Studies on the digestibility of soya bean products, cereal, cereal and plat by-products in diets of dogs. J. Sci. Food Agric. 33:813.
4. Meyer, H. 1980. Nutrient digestibility and its relationship to alimentary disorders in dogs. In: R.S. Anderson (Ed.) Nutrition of the dog and cat. P. 55. Pergamon Press, Oxford.
5. Kendall, P.T., D.W. Holme, P.M. Smith. 1982. Methods of prediction of the digestible energy content of dog foods from gross energy value, proximate analysis and digestive nutrient content. J. Sci. Food Agric. 33:823.
6. Wiernusz, C.J., R.G. Shields Jr., D.J.V. Vlierbergen, P.D. Kigin, R. Ballard. 1995. Canine nutrient digestibility and stool quality evaluation of canned diets containing various soy protein supplements. Vet. Clin. Nutr. 2:49.
7. Bednar, G.E., S.M. Murray, A.P. Patil, E.A. Flickinger, G.C. Fahey, N.R. Merchen. 1998. Selected animal and plant protein source on nutrient digestibility and fecal characteristics of ileal cannulated dogs. Proceedings of 1998 Purina Nutrition Forum, St. Louis, MO.
8. Kritz-Silverstein D, Von Muhlen D, Barrett-Connor E, Bressel MA. 2003. Isoflavones and cognitive function in older women: the Soy and Postmenopausal Health In Aging (SOPHIA) Study. Menopause. 10:196-202.
9. Setchell KD, Cassidy A. 1999. Dietary isoflavones: Biological effects and relevance to human health. J Nutr. 129:758S-767S.
10. Sites C, Cooper B, Toth M, Gastaldelli A, Arabshahi A, Barnes S. Effect of a daily supplement of soy protein on body composition and insulin secretion in postmenopausal women. Fertility and Sterility, 2007 (in press).
11. Pan YL. 2006. Use of soy isoflavones for weight management in spayed/neutered dogs. FASEB J. 20:A854-A855.
12. Pan YL. 2007. Effects of isoflavones on body fat accumulation in neutered male and female dogs. FASEB J. 21:551.20.
13. Uesugi T, Toda T, Tsuji K, et al. Comparative study on reduction of bone loss and lipid metabolism abnormality in ovariectomized rats by soy isoflavones, daidzin, genistin and glycitin. Bio Pharm Bull 2001; 24:368-372.
14. USDA-Iowa State University Database on the Isoflavone Content of Foods – 1999.
15. Pan YL. 2007, unpublished data.