By Joan Brookhyser, RD, CSR, CD Soy is the buzzword in nutrition, as Ipod® is the buzzword in music. It seems you cannot pick up a magazine or newspaper without hearing it. What is it? Do you need it? Of course with soy, there is the additional concern of how the nutrients fit with chronic kidney disease (CKD). Is it safe? How much should you eat? Plant proteins are sometimes discouraged with CKD because of potassium, phosphorus or quality of this protein. How does soy protein fit into the needs of people with CKD? Sometimes animal proteins are not desirable to people with CKD. For others, they prefer not to eat animal proteins, due to religious, cultural or other ethical reasons. Therefore, soy may be a perfect option to meet some of your protein needs. Quality of Soy The quality and amount of protein you eat are of concern with CKD. Too much protein may hurry kidney damage. Too much poor-quality protein may increase urea nitrogen waste build up in your blood, making you tired, possibly causing more complications with your CKD. Soy protein is a good alternative to both of these concerns. Amino acids make up the protein you eat. All foods have varying amounts of these amino acids. The portion of these amino acids determines what foods are low in protein, quality protein or poor quality protein. Up until the last 10 years, the egg was considered the perfect protein, not far behind were other animal proteins, such as meat, poultry and fish. However, recent research shows soy protein also has a very good balance of amino acids required by the human body and is very close to the egg in this regard. Mineral Content of Soy Some soy products are high in potassium and phosphorus. The most common high-potassium soy food is natto (a Japanese paste), soy flour and soy nuts. High-sodium soy foods are miso, soy cheeses and many meat analogues, such as tofu hotdogs, some garden burgers and other meat substitutes. Phosphorus tends to be higher in soy nuts and beans. However, because of the phtytate content of these foods, this may also block some phosphorus from being absorbed. To be safe, use these in moderation. Below, is a list of many soy foods and how best to minimize excess of those high in these minerals. The best foods to fit into your diet are tofu, tempeh and soymilk. Tofu and tempeh are great alternatives to meat in many recipes and casseroles. Soymilk has half the phosphorus of regular milk and is a great alternative to milk products, which often need to be limited in kidney disease treatment. Benefits of Soy In addition to matching animal protein in quality, soy goes beyond animal products in many other benefits. Soy protein contains two phytoestrogens, called isoflavones, which have been found to have many positive roles in kidney disease. Compared with casein, dietary soy has been found to slow the progression of chronic renal injury in animals. Other studies have shown soy to decrease proteinuria. Other studies suggest a decrease in pro-inflammatory cytokines, possibly helping with the decrease in kidney disease progression. Most soy studies show a decrease in cholesterol and other lipids in the blood, suggesting a lipid-lowering effect that contributes to these results. Soy protein has also been found to have protective mechanisms against heart disease, which are often present in kidney patients. Working Soy into Your Diet If you are already on a protein-modified diet, soy can be worked into your diet quite nicely by substituting the ounce equivalent of protein listed in the table provided to the right. If you are not on a restricted protein diet, you can begin to add soy to your diet in place of meat. In any event, you will want to check with your doctor and renal dietitian to help with concerns you may have. Soymilk can be used as a milk replacement in cereal and recipes. The only problem is using soy in instant puddings or custard. Soy does not firm up these products like milk. Tofu is great for a meal replacement in stir-fries, soups and casseroles. Tempeh is a fermented soy product that can be substituted in recipes. It provides a firmer texture with a nutty mushroom flavor. Meat analogues are a great way for healthy fast foods. To avoid excess sodium, minimize these foods. Product Choices Are there any risks with using soy? As noted above, it is best to be careful of any soy foods high in potassium and sodium and keep their use to a minimum. In addition, if you are on hormone replacement therapy you may want to keep your soy intake to one serving (3 oz) per day at most. Isoflavones can act like weak estrogen, conflicting with the estrogen replacement therapy. Excess soy has been thought to be a risk with breast cancer survivors. Small amounts are okay, but soy supplements should be avoided. Keeping in mind that isoflavones in soy act as a drug, taking a supplement of phytochemical has unknown effects. GOOD CHOICES (Approximately 1/4 -1/2 tofu or tempeh = 1 oz animal protein) • Tofu • Tempeh • Garden burgers (<500 mg sodium per serving) • Soy Milk USE IN MODERATION (Limit one per day and limit bold items only if on potassium restriction) • Soy Nuts (1/4 cup) • Soybeans dried cooked (1/2 cup) • Edamame soybeans (1/2 cup) • Soy Flour ( 1/4 cup) • Natto (1/3 cup) • Meat Analogues (>500 mg sodium per serving) • Miso (1 tablespooon) • Soy cheese (3 oz) Joan Brookhyser is a registered dietitian, board certified in renal nutrition. She has been a renal dietitian for 21 years. She frequently speaks and writes on vegetarianism and kidney disease and is a vegetarian herself. She recently published the book “The Vegetarian Diet for Kidney Disease Treatment,” available at www.authorhouse.com. References: Pellett, Peter, Protein Requirements in Humans, Amer J Clin Nutr, 51:723-37, vol 339:1990;1131-1134 Patel, Chaya, Vegetarian Renal Diet and Practical Applications; Renal Nutrition Forum ADA Vol 19, No.3, summer 2000 Soroka, N, Silver berg, DS, Greemland, M, et al, Comparison of a vegetable-based (soya) and an anial-based low-protein diet in predialysis chronic renal failure patients. Nephron, 1998l 79 (2):173-80 Melina, Vesanto, Davis, Brenda, Harrison, Victoria. Becoming Vegetarian. Book Publishing Company, Summertown, Tennessee, 1995 Tovar AR, Murguia, F. Cruz, C, Hernandez-Pando R (et al), A soy protein diet alters hepatic Lipid metabolism gene expression and reducers serum lipids and renal fibrogenic cytokines in rats with chronic nephrotic syndrome. Journal of Nutrition, 2002 Sept;132(9):2562-9 D-Amico G, Gentile MG, Influence of diet on lipid abnormalities in human renal disease. American Journal of Kidney Diseases. 1993. Jul;22(1):151-7 Bhathena, SJ, Velasquez, MT, Protective effect of dietary phytoestrogens in chronic renal disease. Journal of Renal Nutrition. 2001 Oct; 11(4):183-093 Bhathena, SJ, Velasquez, MT, Dietary phytoestrogens: A possible role in renal disease protection. American Journal of Kidney Disease Anderson, JW, Smith BM, Washnock, CS, Cardiovascular Benefits of dry bean and soybean intake. American Journal of Clinical Nutrition. 1999 Sept;70 (3 supp):464S-474S Wholehealthmd.com
The information contained herein is intended for educational purposes only. It is not intended and should not be construed as the delivery of medical care. Persons requiring diagnosis or treatment, or those with specific questions, are urged to contact their local healthcare provider for appropriate care. This article originally appeared in the March/April 2005 issue of Kidney Beginnings: The Magazine, Vol. 4, No. 1.
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