A medium-sized United States study (Alekel et al.) evaluated the effects of soy protein with isoflavones on bone in perimenopausal women. This was a double blind study of 69 women who were divided into three groups: isoflavone-rich soy, isoflavone-poor soy, or whey (control). Smokers were excluded from the study and the medium age of subjects was 50.6.
Diet, physical activity, hormonal levels and bone mineral density were evaluated before and during the 24 week study. All three groups were fed muffins (with the three different ingredients in them and were given powder to mix with food or beverages. They had a high level of subject compliance (the majority of subjects ate most of the muffins) which they evaluated by doing urine analysis. The control group was the only group that showed bone loss. The isoflavone-rich soy had a positive effect on change in bone mineral density.
Weight gain did not confound the results nor did physical activity explain some of the variability in bone loss that was observed. The researchers concluded that soy isoflavones are a benefit to perimenopausal women who can't or don't want to take HRT. The primary limitation of the study was the small sample size.
An Italian study (Chiechi et al.) evaluated the effects of soy rich diet in preventing osteoporosis in postmenopausal women. The study had 187 subjects, ages 39-60 and excluded women who drank alcohol. The 187 diverse subjects were divided into three groups: Diet group, HRT group, and the control group. The diet group was instructed to include one soy food serving per day (e.g., soymilk, miso soup, tofu, tempeh or soybeans).
Compliance in the diet group was assessed by urinary analysis. In addition, the women in the diet group often reported a dislike of soy and difficulty in finding and cooking soy foods. More than half of this group discontinued the study, while only around 80% did in the HRT and control groups.
The control group had bone loss, while both the HRT and the diet groups did not. Overall, diet was not found to be as effective as HRT in preventing bone loss. However, the diet group was found to have high levels of osteocalcin which is an indicator for bone formation. The study was conducted for three months. The researchers concluded that the most troubling outcome of their study was low compliance with their proscribed diet.
A small Scottish study (New et al.) evaluated the effectiveness of a diet rich in fruit and vegetables and bone health. This was a cross-sectional (non-homogeneous group) consisting of 62 healthy women, aged 45-55. Hormonal status was monitored and women were grouped in pre-, post- and perimenopausal groups. Past dietary habits were assessed with the two main groups being: childhood (< 12 y) and early adulthood (20-30y). They were unable to get information from the ages of 12-20y due to the fact that women had a much more difficult time answering questions that pertained to those years. The researchers concluded that this was due to the fact that women have "tremendous change" during that time period. Current physical activity levels were evaluated as well.
Bone mass, markers of bone metabolism and dietary intake were measured within a short time period (< 6 wk). Higher intake of magnesium, potassium and alcohol were associated with higher bone mass. The researchers called the association with alcohol intake and bone mass to be an "intriguing finding." They did not find a significant difference in the variables of bone mineral density and bone metabolism between smokers and nonsmokers, though they found what they called "nutrient differences" between smokers and nonsmokers. The smokers had a higher fat intake than nonsmokers and a lower intake of vitamin C, potassium, and calcium.
The limits of the study include that it was cross-sectional and that the number of subjects studied was relatively small. Thus, the researchers cautioned against making causal relationships and preferred to state that there may be an association between diet and bone health. They concluded that a long-term diet of alkaline-forming foods (including fruits and vegetables) is beneficial.
Alekel, D., St Germain, A., Peterson, C., Hanson, K., Stewert, J., & Toda, T. (2000). Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. American Journal of Clinical Nutrition, 72, (3), 844-852.
Chiechi, L., Secreto, G., D'Amore, M., Fanelli, M., Venturelli, E., Cantatore, F., Valerio, T., Laselva, G., & Loizzi P. (2002) Efficacy of a soy rich diet in preventing postmenopausal osteoporosis: the Menfis randomized trial. Maturitas, 42, (4), 295-300.
New, S., Robins, S., Campbell, M., Martin, J., Garton, M., Bolton-Smith, C., Grubb, D., Lee, S., & Reid, D. (2000). Dietary influences on bone mass and bone metabolism: further evidence of a positive link between fruit and vegetable consumption and bone health? American Journal of Clinical Nutrition, 71, 142-151.