Obesity and Risk of Kidney Stones

Obesity and weight gain may increase the risk of kidney stone formation, especially in women, reported Eric N. Taylor, M.D., of Brigham and Women's Hospital, Harvard Medical School, Boston.

He and his associates prospectively studied three cohorts: the Health Professionals Follow-Up Study (45,988 men, age 40–75 years at baseline), the Nurses' Health Study (NHS) I (93,758 older women, age 30–55 years at baseline), and the Nurses' Health Study (NHS) II (101,877 younger women, age 25–42 years at baseline). Over a combined 2.8 million person-years of follow-up, the incidence of new symptomatic kidney stones was 4,827.

After adjustment for age, dietary factors, fluid intake, and thiazide use, the relative risk of kidney stone formation in men weighing more than 220 pounds was 1.44, compared with men weighing less than 150 pounds. When comparing the same weight categories, the relative risk was 1.89 in NHS I (older women) and 1.92 in NHS II (younger women), the researchers said (JAMA 2005;293:455–62).

For men who gained more than 35 pounds after age 21, the relative risk for stone formation was 1.39, compared with men whose weight did not change. For women who gained more than 35 pounds after age 18, versus those whose weight held steady, the relative risk was 1.70 in NHS I and 1.82 in NHS II.

Body mass index (BMI) also was a factor. In men, the relative risk of stone formation was 1.33 with a BMI of 30 kg/m2 or higher, compared with men who had a BMI of 21–22.9 kg/m2. For women, the same BMI categories were associated with a relative risk of 1.90 in NHS I and 2.09 in NHS II.

For men with a waist circumference greater than 43 inches, the relative risk was 1.48, compared with those whose waist circumference was less than 34 inches. The relative risk for women with a waist circumference greater than 40 inches versus women with a waist circumference less than 31 inches was 1.71 in the older women and 1.94 in the younger women.

Diets and Cardiac Risk Factors

Four popular diets all appear to reduce body weight and several cardiac risk factors at 1 year, but the benefits are modest, apparently because of low adherence, said Michael L. Dansinger, M.D., of Tufts-New England Medical Center, Boston.

In a single-center, randomized trial of adults with a mean BMI of 35 kg/m2 and at least one metabolic cardiac risk factor, 160 patients were evenly divided among the diets: Atkins (carbohydrate restriction), Zone (macronutrient balance), Weight Watchers (calorie restriction), or Ornish (fat restriction). For the first 2 months, patients were told to make a maximum effort to adhere to the diet. At 2 months, 21% had dropped out; the percentage rose to 38% at 6 months and 42% at 1 year (JAMA 2005;293:43–53).

In the primary intent-to-treat analysis, mean weight loss at 1 year was 4.8 pounds for Atkins (52% completed the study), 6 pounds for Zone (65% completed), 4.9 pounds for Weight Watchers (65% completed), and 7.3 pounds for Ornish (50% completed). There was no significant difference between diets.

All four diets modestly reduced mean LDL-cholesterol levels at 1 year, except for Atkins. All diets significantly increased mean HDL-cholesterol levels, except for Ornish. The LDL/HDL ratio fell about 10% at 1 year. There were no effects on triglycerides, blood pressure, or fasting glucose.

“Poor sustainability and adherence rates resulted in modest weight loss and cardiac risk factor reductions,” the researchers said.

Protecting Bone During Dieting

Even modest weight loss from exercise training is associated with a reduction in bone mineral density (BMD), particularly in women who are not taking raloxifene or hormone therapy (HT), reported Wendolyn S. Gozansky, M.D., of the University of Colorado, Denver.

In a 6-month, randomized double-blind, placebo-controlled study of postmenopausal, sedentary, overweight women aged 50–70 years, 68 participated in a supervised exercise training program of moderate intensity and 26 control subjects did not participate. Both groups were separately randomized to one of three treatment groups: placebo, raloxifene, or HT (J. Clin. Endocrinol. Metab. 2005;90:52–9).

Women in the control group had a mean weight gain of 0.8 kg; those in the intervention group had a mean loss of 4.1 kg.

In the control group, the average percent change in BMD across all measured skeletal sites was a 0.6% reduction in placebo users (n = 7), a 0.9% gain in raloxifene users (n = 9), and a 3.0% gain in HT users. In the intervention group, BMD declined 1.5% in the placebo group (n = 22), fell 0.5% in the raloxifene group (n = 23), and rose 1.1% in the HT group (n = 23).

“Being overweight does not necessarily confer protection against low BMD in postmenopausal women,” the researchers said.

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