Objectively Measured Physical Activity and Body Fat Gains in Women

Abstract

PURPOSE: To determine the extent to which objectively measured physical activity (PA) affects risk of weight and body fat gains in middle-aged women. A secondary aim was to ascertain the extent to which age and energy intake confound the above associations. METHODS: A prospective cohort design was used with 4 yrs between the baseline and follow-up assessments. Subjects were 166 women who were non-smokers and non-obese (BMI <30), with a mean age of 41.4 (+ 2.9) years, at baseline. At baseline, subjects wore a CSA (now MTI) accelerometer over the left hip for 7 consecutive days. The sum of all activity counts was used to index PA. PA was divided into quartiles and the middle-two quartiles were collapsed to form three PA groups (Low, Moderate, High). Body weight was measured using a computerized scale and body fat percentage was assessed using DXA (Hologic, 4500W). Energy intake was measured using weighed food logs kept during the same 7 days subjects wore the accelerometers. Everything eaten was first weighed on an Ohaus digital scale and then recorded on a food log. A registered dietitian entered all of the food record data, and energy intake was computed using the Esha Research software. RESULTS: Mean weight change over the 4 yrs was 1.0+ 5.0 kg. Mean change in body fat percentage was 1.5 + 3.7 percentage points. Weight change over the 4 yrs differed significantly across the three PAgroups (F = 3.9, P = 0.023). Women in the Low PA (2.2 + 5.3 kg) and Moderate PA (1.2 + 5.0 kg) groups gained significantly more weight over the 4-year study compared to those in the High PA group (−0.7 + 4.3 kg) who lost weight. Similarly, women in the Low PA (2.4 +3.8 % points) and Moderate PA (1.7 + 3.1 % points) groups gained significantly more in body fat percentage than those in the High PA (0.3 + 4.2 % points) group (F = 3.6, P = 0.031). Adjusting for age and energy intake had little effect on the associations. Incidence data used to calculate relative risk showed that the risk of gaining ≥3.5 kg over the 4 yrs was 3.2 times greater for women in the low PA group compared to those in the high PA group (95% CI: 1.3–7.9). Risk of gaining 3.5 kg or more was 1.7 times greater in the Low PA group compared to the Moderate PA group (95% CI: 1.0–2.9). The likelihood of losing 1 kg or more of body weight over the study was 1.5 times greater in the High PA group compared to the Low PA group (95% CI: 1.1–2.0). CONCLUSIONS: Middle-aged women who engage in low levels of physical activity are at greatly increased risk of weight and body fat gains over a 4-year period compared to women who engage in higher levels of activity. Similarly, high physical activity levels increase the likelihood that women will lose weight and body fat over 4 yrs compared to low levels of activity.