The respiratory quotient as a prognostic factor in weight-loss rebound

To investigate the possible metabolic factors predisposing to weight gain subsequent to the cessation of a rapid-weight-loss diet.

Prospective, longitudinal, intervention study of a 2 MJ diet daily for 28 d in a metabolic ward followed by a 12-month outpatient follow-up under a conventional, hypocaloric diet.

Thirty-five females and one male, all with morbid obesity defined by a body mass index > or = 35 kg/m2.

VO2 and VCO2 measured by 30 min indirect calorimetry to calculate resting energy expenditure and resting respiratory quotient at the beginning and end of very-low-calorie diet; body composition assessed by hydrostatic weighing on day 1; weight recorded on days 1 and 28 and at follow-up of 3, 6 and 12 months.

From among all the variables considered, the resting respiratory quotient measured on day 28, even adjusted for weight loss during hospitalisation, was the only one that correlated significantly with the weight changes recorded during follow-up.

Subjects who showed a respiratory quotient on day 28 in the lower range (< 0.72) were more able to maintain the weight-loss achieved with the very-low-calorie diet while those in the higher range (> 0.75) were less able to do so over the follow-up period. Thus, an appropriately measured respiratory quotient could prove useful in clinical practice as a prognostic marker of the long-term effectiveness of low- and very-low-calorie diets used to induce rapid weight loss.