In societies that consume soy products, the populations have a lower incidence of osteoporosis. The soy components thought to be responsible for this are the isoflavones genistein and daidzein.
Isoflavones are secondary vegetable substances, which can act as estrogens in the body and have protective functions, explains LSU AgCenter nutritionist Dr. Heli Roy.
Genistein binds with estrogen receptors at cell membranes and causes cellular changes similar to estrogen. In terms of bone changes, stimulation of estrogen receptors by estrogen or by soy isoflavones causes increased bone building and reduced bone breakdown.
"Our bones are living parts that are broken down and re-built continuously," Roy says, adding, "In an ideal world, once we have matured and developed strong bones, the building and breaking down would happen at the same rate so our bones would stay as strong as they were during our youth. Newer bones would continue to replace older bones."
The nutritionist notes, however, there are many instances where bone breakdown occurs at a higher rate than bone building. Causes include inactivity and lack of estrogen, vitamin D and calcium. Also as we age, bone breakdown occurs at a higher rate than re-building. Inactivity reduces bone mass significantly; this is why forced bed rest can many times lead to fragile bones.
At the other end of the spectrum, bone re-building occurs at a higher rate during growth and development because of estrogen and when bone is stressed, such as during weight training.
Weight lifting is a stress on the bone, and when applied during regular intervals, it helps to increase bone strength. The stress causes additional bone matrix to be built, and calcium is then deposited on that matrix.
Bone rebuilding is regulated by a fine balance of hormones and enzymes. Roy says for bone re-building to occur, there has to be a protein or collagen matrix to which calcium is then deposited. Eating a diet high in soy with soy isoflavones increases the building of the collagen and the protein matrix.
Once the matrix is built, we obviously need enough vitamin D and calcium to be able to deposit it in the matrix. Sources of calcium are dairy products, greens and bony fish. Soy is also a good source of calcium.
Calcium also is added to traditionally low-calcium foods such as orange juice, which becomes an excellent source of calcium for those who are lactose intolerant and cannot have milk.
Lactose-intolerant people may be able to eat yogurt, many cheeses and ice cream. There are also lactase products that can be taken to supplement the lactase enzyme. Supplemental calcium can also be taken in pills, tablets and chews.
Soy products come in many forms: tofu, soy milk, soy cheeses, edamami (soybeans in the pod), dry soybeans, soy flour and textured vegetable protein. Tofu can be incorporated into almost any mixed recipe such as casseroles or soups. Dried and salted soybeans can be used in place of peanuts in many recipes without any change in the taste of the product.
On the Internet: LSU AgCenter: www.lsuagcenter.com
Source: Heli Roy (225) 578-4486, or HRoy@agcenter.lsu.edu