The Effects of Soy Protein Supplementation on Lipid Profiles and Bone Biomarkers

The attention to the role of functional foods in preventing and reversing disease processes has grown in recent years, as has the identification of specific functional foods with multiple health benefits. In the United States, cardiovascular disease is still the leading cause of death, while osteoporosis is the most common skeletal disorder as well as a major cause of morbidity and mortality in both women and men. In osteoporotic individuals, the rate of bone resorption often exceeds the rate of bone formation, leading to net bone loss. Hyperlipidemia as a measure of cardiovascular health and the net bone loss in regards to osteoporosis have both been shown to be influenced by diet. Soy proteins have been shown to reduce blood cholesterol levels, likely due to both the upregulation of low‐density lipoprotein (LDL) receptor activity as well as the estrogen‐like properties of its isoflavones. Soybean isoflavones also have beneficial effects on bone health due to their estrogen‐like properties, albeit not all studies have supported this. Thus, the objective of this study was to determine the effects of soy protein on lipid profiles and bone metabolism in adults. To this end, 90 men and women were randomly assigned to consume 40 g of protein per day in the form of either soy or casein for three months. Soy consumption reduced bone‐specific alkaline phosphatase activity, a marker of bone formation and/or turnover, significantly ( P <0.03); however, soy also tended to decrease ( P <0.08) tartrate‐resistant acid phosphatase 5b activity, a marker of bone resorption. Soy also significantly increased serum insulin‐like growth factor‐I concentrations ( P <0.0001), which is known to stimulate osteoblast proliferation and differentiation. Soy protein did not significantly lower serum levels of total‐cholesterol, LDL‐cholesterol, or lipoprotein(a), or increase high‐density lipoprotein (HDL) levels. The results of this study demonstrate that soy protein isolate given as a daily supplement has positive effects on some indices of bone metabolism in both men and women, while having little effect on total‐, HDL‐, and LDL‐cholesterol concentrations in normolipidemic and mildly hypercholesterolemic men and women. Future mechanistic studies may be warranted to understand the role of soy protein in bone health.