Whoever said weight loss was a straightforward process has probably never tried to go from a BMI of 40 down to 24 kg/m2. I must admit that some years back, in the early stages of my graduate training, I was equally naive. It’s a case of simple math, I then believed – once your energy expenditure exceeds your energy intake, you lose weight.
It certainly sounds simple, and yet it rarely is that simple in practice.
Take for example a small study by King et al. where 35 overweight and obese sedentary men and women were prescribed exercise five times per week for 12 weeks under supervised conditions. Following the 12 weeks of standardized exercise intervention, the mean reduction in body weight was 3.7±3.6 kg.
Importantly, this mean change obscured the vast individual variability in weight change, which ranged from a loss of 14.7 kg to a gain of 1.7 kg.
The authors of this study postulated that some individuals compensated for their increased exercise by a reduction in the resting metabolic rate and/or an increase in hunger and associated energy intake.
Another study published by Gasteyger and colleagues investigated the effect of the size of the weight loss centre, in terms of numbers of participants recruited, on the weight loss achieved among the study participants.
In the study, the authors looked retrospectively at data collected during a prior multicenter trial to see if the size of the study center (how many people were recruited to lose weight at site A versus site B, for example) had any influence on the success of the weight loss treatment.
In total, 22 different centers recruited anywhere from 4 up to 85 participants to undergo a 8 week low calorie diet. The subjects BMIs were in the range of high 30’s to low 40’s (class 2 and 3 obese).
At the end of the intervention the average weight loss among all the subjects was approximately 10 kg (or 10% of initial body weight) – not bad for 8 weeks!
However, the average weight loss for a given weight-loss center ranged from 5.8 to 11.8% – despite the exact same intervention.
Interestingly, the authors found a relationship between the number of subjects recruited at each center and the average degree of weight loss observed among those subjects.
Specifically, for every increase in 10 subjects to the center’s study population, the expected average weight loss for participants in that center increased by approximately 0.5%!
So if two obese people joined the same weight-loss study, the one who joined a bigger center, with more subjects, would be expected to lose more weight on the exact same plan.
How do we explain these findings?
Here’s the authors’ best guess:
“The main reason for the correlation between weight loss and the number of recruited subjects per center may be that principal investigators, study coordinators, and dieticians working at centers with high numbers of recruited subjects have more experience than those working at smaller centers; therefore, they are probably more efficient in treating and counseling subjects during a low calorie diet.”
Take home message:
- If you and a friend go on the exact same weight loss plan, don’t be discouraged if you do not experience the exact same level of weight reduction.
- If you’re seeking out weight-loss help from a professional weight loss clinic, it would appear that visiting the most-highly trafficked clinic is the way to go.
- King et al. Individual variability following 12 weeks of supervised exercise: identification and characterization of compensation for exercise-induced weight loss. International Journal of Obesity (2008) 32, 177–184; doi: 10.1038/sj.ijo.0803712
- Gasteyger, C., Christensen, R., Larsen, T., Vercruysse, F., Toubro, S., & Astrup, A. (2010). Center-Size as a Predictor of Weight-Loss Outcome in Multicenter Trials Including a Low-Calorie Diet Obesity, 18 (11), 2160-2164 DOI: 10.1038/oby.2010.118