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In the Vegetarian & Vegan News...
From
American Journal of Clinical Nutrition
March 2001 (Volume 73)

Back A High Ratio of Dietary Animal to Vegetable Protein Increases the Rate of Bone Loss and the Risk of Fracture in Postmenopausal Women

Sellmeyer DE, Stone KL, Sebastian A, et al.
Am J Clin Nutr. 2001;73:118-122

The hypothesis that a high dietary ratio of animal protein to vegetable protein increases bone loss and risk of fracture was studied in a prospective cohort of 1035 women who participated in the Study of Osteoporotic Fractures (SOF). White community-dwelling women were recruited for the study and were aged > 65 years.

Recent dietary history (over the preceding 12 months) was assessed using a "validated" food frequency questionnaire. Intakes of protein were calculated from this questionnaire. BMD was measured using DXA at the total hip and subregions. Two BMD measurements were taken with an average of 3.6 years (SD 0.4 years) between each assessment. The rate of bone loss was calculated as the percentage difference between 2 BMD measurements in a subset of the participants (n = 742). Hip fractures were assessed prospectively for 7 years (SD 1.5 years), and fracture data were available for all the 1035 women for whom the dietary data were collected. Fractures were confirmed with radiographs and a review of the radiologist reports.

Results were intriguing. Women with a higher ratio of animal to vegetable protein intake had a higher rate of bone loss at the femoral neck than did those with a low ratio, as well as a greater risk of hip fracture (relative risk = 3.7). These findings remained significant after adjustment for important confounding factors, including age, weight, estrogen use, tobacco use, physical activity, and total Ca and protein intake.

These findings provide further support for a link between vegetable-based proteins and indices of bone health and suggest that a decrease in animal protein and an increase in vegetable protein may decrease bone loss and risk of hip fracture.

Clinical Commentary

This is a fascinating study by Professor Anthony Sebastian (Division of Endocrinology) and Professor Steven Cummings (Department of Epidemiology and Biostatistics) from the University of California, San Francisco. The Study of Osteoporotic Fractures (SOF) is currently the largest population-based investigation (N = 9704 white women aged > 65 years) and has been the focus of some very important publications over the past decade.[1] Sebastian and his colleagues have been at the forefront of the field linking the skeleton to acid-base balance, and his 1994 paper is key to demonstrating that diets rich in animal foods and low in vegetable foods can lead to a dietary net acid load that has a negative effect on Ca balance and markers of bone turnover.[2]

This paper provides further support for a randomized, controlled supplementation trial of fruit and vegetables, or animal- vs vegetable-based proteins, on indices of bone health and lends further support to the idea of a link between acid- and alkaline-forming foods.

The role of the skeleton in acid-base balance has been gaining increasing prominence in the literature from a combination of experimental (at the human, animal, and cellular level), clinical, and observational studies.[3,4] As shown in Table 3, there have been a number of population-based studies suggesting a positive association between high intakes of fruit and vegetables and bone health, with remarkable similarities of findings in 2 of the largest (and most recent) nutrition and bone health observation studies.[5-7]

Table 3. Impact of Fruit and Vegetables on Bone: A Review of Population-Based Studies Showing a Positive Link

Author Year Country Details Findings
Eaton-Evans et al 1993 UK 77 females, 46-56 years Vegetables
Michaelsson et al 1995 Sweden 175 females, 28-74 years K Intake
New et al 1997 UK 994 females, 45-49 years K, Mg, fiber, vitamin C
Past intake of fruit & vegetable
New et al 1998 UK 164 females, 55-87 years K, fruit & vegetables
Tucker et al 1999 USA 229 males: 349 females, 75 years K, Mg, fruit & vegetables
New et al 2000b UK 62 females, 45-54 years K, Mg, fiber, vitamin C
Past intake of Fruit & Vegetable
denotes positive effect of nutrients with indices of bone health
Source: New SA. Nutrition, exercise and bone health. Proceedings of the Nutrition Society 2001;60(2):265-274. Reproduced with permission

The findings of the first population-based fruit and vegetable intervention trial (Dietary Approaches to Stopping Hypertension - DASH) provide further support for this theory. This study showed, as a secondary finding, a positive effect on Ca economy.[8] An increase in fruit and vegetable intake from 3.6 to 9.5 daily servings decreased urinary Ca excretion from 157 mg/24 hours to 110 mg/24 hours.

The fruit and vegetable link to bone health is an exciting area for further research. Suprisingly, the theoretical considerations have been discussed for over 3 decades,[9] but only recently have they received much greater attention.[10-12]

References

  1. Cummings SR, Eckert S, Krueger KA, et al. The effects of raloxifene on risk of breast cancer in postmenopausal women: Results from the MORE randomised trial. JAMA. 1999;281:2189-2197.
  2. Sebastian A, Harris ST, Ottaway JH, et al. Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate. N Engl J Med. 1994;330:1776-1781.
  3. New SA. Nutrition, exercise and bone health. Proceedings of the Nutrition Society. 2001;60:265-274.
  4. New SA. Fruit & vegetable consumption and skeletal health - is there a positive link? Nutrition Bulletin. British Nutrition Foundation, London. 2001 (in press).
  5. New SA, Bolton-Smith C, Grubb DA, Reid DM. Nutritional influences on bone mineral density: a cross-sectional study in premenopausal women. Am J Clin Nutr. 1997;65:1831-1839.
  6. New SA, Robins SP, Campbell MK, et al. Dietary influences on bone mass and bone metabolism: further evidence of a positive link between fruit and vegetable consumption and bone health? Am J Clin Nutr. 2000;71:142-151.
  7. Tucker KL, Hannan MT, Chen H, Cupples A, Wilson PWF, Kiel DP. Potassium and fruit & vegetables are associated with greater bone mineral density in elderly men and women. Am J Clin Nutr. 1999;69:727-736.
  8. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. N Engl J Med. 1997;336:1117-1124.
  9. Wachman A, Bernstein DS. Diet and osteoporosis. Lancet. 1968;I:958-959.
  10. New SA. Impact of food clusters on bone. In: Nutritional Aspects of Osteoporosis 2000 (4th International Symposium on Nutritional Aspects of Osteoporosis. May 17-20, 2000. Lausanne, Switzerland). In: Burckhardt P, Dawson-Hughes B, Heaney RP, eds. A Serono Symposia S.A. Publication. New York, NY: Springer-Verlag. 2001 (in press).
  11. Bushinsky DA. Acid-base imbalance and the skeleton. In: Nutritional Aspects of Osteoporosis '97. Eds Burckhardt P., Dawson-Hughes, B., Heaney R. P. Proceedings of the 3rd International Symposium on Nutritional Aspects of Osteoporosis, Switzerland, 1997. Italy: Ares-Serono Symposia Publications 1998 pp208-217.
  12. Barzel US. The skeleton as an ion exchange system: implications for the role of acid-base imbalance in the genesis of osteoporosis. J Bone Miner Res. 1995;10:1431-1436.

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