Background: Studies have reported inconsistent findings on the association between dairy product intake and weight change and obesity. Only a few prospective studies have investigated the role of dairy consumption in both weight change and risk of becoming overweight or obese and whether these associations depend on the initial body weight.

Objective: We prospectively investigated how dairy product intake was associated with weight change and risk of becoming overweight or obese in initially normal-weight women.

Design: We studied 18,438 women aged ≥45 y from the Women's Health Study who were free of cardiovascular disease, cancer, and diabetes and had initial body mass index (BMI; in kg/m(2)) from 18.5 to <25 at baseline. Dairy intake was assessed with the use of a 131-item food-frequency questionnaire. Women self-reported body weight along with obesity-related risk factors on baseline and annual follow-up questionnaires. At each follow-up time, women were categorized as normal weight (BMI: 18.5 to <25), overweight (BMI: 25 to <30), or obese (BMI ≥30).

Results: During a mean follow-up of 11.2 y, 8238 women became overweight or obese. Multivariable-adjusted mean ± SD changes in body weight during the follow-up (18 y) were 1.90 ± 0.09, 1.88 ± 0.08, 1.86 ± 0.09, 1.82 ± 0.09, and 1.65 ± 0.09 kg in quintiles 1-5 of total dairy intake, respectively (P-trend = 0.003). Greater intake of high-fat dairy products, but not intake of low-fat dairy products, was associated with less weight gain (P-trend = 0.004). In multivariable-adjusted analyses, lower risk of becoming overweight or obese was observed in the highest quintile of high-fat dairy product intake (HR: 0.92, 95% CI: 0.86, 0.99). Dietary or supplemental calcium or vitamin D was not associated with risk of becoming overweight or obese.

Conclusion: Greater consumption of total dairy products may be of importance in the prevention of weight gain in middle-aged and elderly women who are initially normal weight.