A recent study looked at the effect of paying people to lose weight.

The authors randomized 100 people with BMIs ranging from 30 to 39.9 into four groups. Two groups received weight-loss education, one group with and one without payment. The other two groups received education plus behavior modification with, again, one group receiving financial incentives and the other not. To remain in the study, they were all supposed to have lost 4 pounds per month. Patients in the two financial incentive groups received $20 per month if they met their goal, and those not meeting the goal had to pay $20 per month, which was pooled for a lottery among the participants at the end of the study.

A significantly larger percentage of those receiving remuneration completed the study. At the study’s endpoint—12 months, the average weight loss for those in the paid groups was about 9 pounds compared to just over 2 pounds for the two unpaid groups. Using a two-way ANOVA, the incentives were estimated to have led to a weight loss of 6.5 pounds, which was statistically significant with a p value < 0.001.

The authors concluded, “Sustained weight loss may be achieved with financial incentives.”

The paper was presented at the American College of Cardiology meeting last March and is available only in abstract form.

It raises some questions.

The paid groups lost less than 1 lb per month. If the subjects were to have lost 4 lbs per month as stated in the protocol, why didn’t they lose a minimum of 48 lbs, which would be 4 lbs x 12 months?

How durable was the weight loss? In other words, after the monetary incentive stopped, did the subjects regain the weight? It is well-known that many people regain weight after they go off their diets.

Does this study actually show that education and behavior modification are not very useful in promoting weight loss? Then why should anyone bother?

It’s one thing to do a study of 100 people, but if money truly is a good way to get people to lose weight, who is going to pay the millions of obese people in the US?

But here’s the real question. How clinically important is a 6 to 9 lb weight loss for someone with a BMI of, say, 35?

If a man is 5’8″ tall and weighs 230 lbs, he has a BMI of 35. If he loses 6 lbs, his BMI drops to 34. Does that decrease his risk for diabetes or hypertension? I think not.

This may be another example of a statistically significant result that is very likely not clinically important.

Skeptical Scalpel is a retired surgeon and was a surgical department chairman and residency program director for many years. He is board-certified in general surgery and critical care and has re-certified in both several times. He blogs at SkepticalScalpel.blogspot.com and tweets as @SkepticScalpel. His blog averages over 1400 page views per day, and he has over 9400 followers on Twitter.