Eat for Your Heart or Bones? It's a Tradeoff

Summarized by Robert W. Griffith, MD
February 12, 2004

Introduction

We tend to give over-simplistic advice about diet - limit calories, eat 5 servings of fruit or produce a day, avoid saturated fats, and so on. Unfortunately, it's not always simple. A recent study has exposed an important tradeoff between a heart-healthy diet and a bone density building diet. It was published in the American Journal of Clinical Nutrition, and commented in an editorial.¹

What was done

A group of 891 women aged 45 to 55 had bone mineral density (BMD) examinations of the lumbar spine and the neck of the femur. They completed a questionnaire about their normal diet and physical activity, and had a physical exam. Five years later they returned for a second BMD scan and questionnaire.

What was found

Most of the women were premenopausal at the start of the study, and none had taken hormone replacement therapy (HRT). Five years later, only 16% were still menstruating, and 45% had taken HRT. Body weight and body mass index (BMI) had, on average, increased, and BMD had decreased.

Higher calcium intake and modest alcohol consumption were significantly linked to a lessened decrease in BMD, i.e. they had a mild protective effect on the risk of osteoporosis. On the other hand, an increased intake of poly- and mono-unsaturated fatty acids (usually regarded as being heart-healthy) was linked to a greater BMD loss.

In those women who were still menstruating, a higher intake of fruit and vegetables was linked to an improved BMD, compared to the other participants. The scientists assumed that the calcium, vitamin C, magnesium, and potassium found in fruits and vegetables were responsible for the slowing of BMD loss.

Comment

The 'negative' effects of fatty acids on BMD found in this study are puzzling. There are several theories as to why this should be, based on animal studies, but they all remain unproven. The results show, however, that too great consumption of mono- and poly-unsaturated fatty acids accelerates the usual age-related loss of BMD, and raises the risk of osteoporosis.

Additional results in this study show that the percentage increase in body weight that they found was linked to a reduction in the loss of BMD - in other words, increasing body weight benefited the bones, though it's well-accepted that it's bad for the heart.

Analysis of many studies has shown that the likelihood of a hip fracture in people with a BMI of 20 (i.e. with a low weight) is twice that of people with a BMI of 25, which is the upper limit of normal, before one speaks of 'overweight'. On the other hand, the risk of hip fracture is greatly increased in people who are seriously obese (a BMI of 40 or more). Obviously, it's important not to be too fat OR too thin.

So, in view of these tradeoffs (fatty acids and thinness both good for the heart but bad for bones), what's the best diet for avoiding both heart disease and osteoporosis? The experts say that this is something that must be tailored to the risks of each person, individually. How to get the best balance can be tricky, and you should get expert advice, if necessary. But you can't go wrong with plenty of fruit and vegetables!

Source

• Nutritional associations with bone loss during the menopausal transition; evidence of a beneficial effect of calcium, alcohol, and fruit and vegetable nutrients and of a detrimental effect of fatty acids. HM. Macdonald, SA. New, MHN. Golden,  et al., Am J Clin Nutr, 2004, vol. 79, pp. 155--165

Footnotes
1. Diet for the heart or the bone: a biological tradeoff. SM. Ott, Editorial. Am J Clin Nutr, 2004, vol. 79, pp. 4--5

Related Links
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How Weight Loss Helps Your Heart
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