Effect of a very-low-calorie diet on body composition and resting metabolic rate in obese men and women.

Many methods of weight reduction have been developed to treat obesity and its resulting risks of morbidity and mortality (1). Most of these have had limited success (2-4). Recent attempts to treat obesity have involved the use of very-low-calorie diets (VLCDs).

The majority of studies on VLCDs have not differentiated between loss of fat and loss of fat-free mass. Moreover, although many programs have used bioelectrical impedance analysis (BIA) to determine percent body fat, BIA may not be valid in obese populations. In addition, limited data characterize changes in waist:hip ratios during treatment with a VLCD. Decline in resting metabolic rate (RMR) with VLCDs has also been reported (5,6), but researchers disagree as to whether this correlates with a decrease in lean body mass (LBM) (7-11).

The purpose of this study was to determine weight loss, body composition, body fat distribution, and RMR in obese subjects before and after 12 weeks of treatment with a VLCD and to compare hydrodensitometry with BIA.

Methodology

Subjects

Seventeen subjects (nine women and eight men) from an outpatient, hospital-based treatment program for obesity volunteered. For women, height ranged from 156.8 to 175.3 cm and weight from 78.2 kg to 117.3 kg. For men, height ranged from 169.5 cm to 189.2 cm and weight from 99.6 kg to 165.5 kg. Subjects ranged in age from 22 to 57 years (Table 1).

Body weight and hydrodensitometry

Informed consents were obtained from all subjects. All measurements were obtained between 5 AM and 8 AM and after subjects had been fasting (except for water) for 12 hours. The same investigator obtained all measurements except the oxygen consumption measurements. Body weight was measured to the nearest 0.25 lb and height to the nearest 0.25 in on a balance beam scale. Subjects wore swimwear or shorts and T-shirt and no shoes. Height and weight measurements were converted to metric units, and body mass index (BMI) was calculated.

Vital capacity was measured by a 13.5-L modular office respirometer.(1) Three trials were performed, and the mean of the greatest two trials was calculated and multiplied by a bell correction factor (41.45 mL/mm), a temperature correction factor, and an age correction factor. A laboratory correction factor of 350 mL was added to obtain the residual volume.

Subjects were weighed in water on a Chatillion scale(2) after maximally exhaling. Subjects wore swimwear or shorts and a T-shirt and a weighted belt (3,620 g). Trials were repeated at least eight times or until consistent measures were obtained and no further increases in weight were noted. Siri's formula was used to obtain percent fat from body density (12).

Bioelectrical impedance analysis

After cleaning all skin contact areas with alcohol, four aluminum-foil spot electrodes were placed on the dorsal surfaces of the right hands and feet, one each at the distal portions of the third metacarpals and metatarsals, one between the distal prominences of the radius and the ulna, and one between the medial and lateral malleoli at the ankle. Bioelectrical resistance and reactance were measured using a computerized bioelectrical analyzer system.(1) Subjects were supine without thigh to thigh, arm to torso, or other extraneous skin contacts. The computerized system converted resistance and reactance to percent …