During weight loss, there is a process of metabolic adaptation that can increase hunger and reduce energy requirements. This is believed to be part of why weight loss maintenance is difficult for many.
But does weight loss always lead to a reduced metabolism, or is this something that only some individuals experience?
In adaptive thermogenesis, the resting energy expenditure (REE) decreases further than what is predicted based on changes in body mass and composition. This is one way that the body is able to adapt the metabolism during weight loss.
There is some research that suggests that REE drops beyond the predicted level, and can persist over the long term. One recent study evaluated 14 contestants from The Biggest Loser, and found that after 6 years, their REE was 500kcal/day lower than predicted. Some researchers suggest that this shows the futility of maintaining weight loss.
However, there may be factors that influence how much metabolic adaptation occurs during weight loss. It could even be that individuals who have minimal or no adaptation are more successful in maintaining weight loss.
With this in mind, researchers designed a case-control study to evaluate whether successful weight-loss maintainers experienced a lower than predicted REE.
Three groups of participants were recruited for the study. One group consisted of 34 weight loss maintainers (WLM) who had maintained a ≥13.6kg weight loss for ≥1 year. There were two control groups – one group of normal weight participants (NC) with a similar BMI to the WLM group, and one of overweight and obese participants (OC) with a similar BMI to the WLM group pre-weight loss.
Researchers measured the REE of each group using indirect calorimetry, which measured the respiratory gas exchange over a 30 minute period. They then calculated predicted REE for the WLM group using the data from the NC and OC group, as well as using 3 standard predictive equations – Harris and Benedict, Mifflin et al. and an equation based on tissue-specific metabolic rates.
The REE of WLMs was accurately predicted using the equations from NCs and OCs, as well as the 3 predictive equations. In the WLM, the difference between the predicted REE and actual REE ranged from -257kcal to +163kcal/day.
A lower REE compared to prediction was correlated with the amount of weight loss, but not the duration of maintenance.
The researchers concluded that they had no consistent evidence of a significantly lower REE than predicted in people who successfully maintained weight loss over a long period of time. They suggested that sustained weight loss may not always cause a substantial reduction in metabolism.
Limitations in the study were noted, such as the limited number of participants with a BMI over 40. This means the results may vary for people with morbid obesity. The WLM sample was 76% female and 100% Caucasian, so further research may be needed to confirm these findings in males and different ethnicities.
Ostendorf, D.M., Melanson, E.L., Caldwell, A.E., Creasy, S.A., Pan, Z., MacLean, P.S., Wyatt, H.R., Hill, J.O. and Catenacci, V.A., 2018. No consistent evidence of a disproportionately low resting energy expenditure in long-term successful weight-loss maintainers. The American journal of clinical nutrition, 108(4), pp.658-666.