Look AHEAD vs. DPP?

One of the articles I came across when researching my last post was called “Diet, Diabetes, and Doubt: Is Preventive Medicine Lost In Space?” by David Katz. I wanted to make a few quick points about it.

Dr. Katz writes:

The AHEAD methodology also helps account for the putatively disappointing results of the long-term study. Diabetes requires treatment—so all patients in AHEAD were treated. Those in the lifestyle intervention group reduced their reliance on medication, while those in the control group took more. But since failing to treat diabetes with state-of-the-art medication is unethical, everyone was provided that. The study was actually comparing feet and forks to pharmacotherapy. When both intervention and control groups are being treated, differences between them diminish, an occurrence known in research as “bias toward the null.” This exerted a profound effect in the AHEAD trial, making the positive findings more noteworthy still.

In other words, the difference between the groups would be greater if neither group had modern medical treatment–but why is that even a relevant question? Are we trying to find out what kinds of benefits people with diabetes would experience if they followed a program similar to those in the intervention group of Look AHEAD compared to normal treatment by their doctors–a practical question–or are we trying to prove that fat=bad? The goal of the study was not to find out how best to treat diabetes in areas with little or no access to medication, or how to treat diabetes in people with bad/no health insurance.

Still, the fact that the study looked at people who already had well-controlled diabetes even before the start of the study and who had access to appropriate medication is an important caveat for people who have poorly-controlled diabetes and/or do not have good access to appropriate diabetes drugs–or for people who are having trouble finding drugs with tolerable side effects. Even if, like me, you are aggressively skeptical about the magnitude of the contribution of BMI to health in order to correct for societal bias in the opposite direction, I think at least the exercise portion of the intervention would be helpful to people with poorly-controlled diabetes.

Also (as implied by Katz’s later words that “both intervention and control groups are being treated”) the study was not comparing “feet and forks to pharmacotherapy”, they were comparing feet and forks plus pharmacotherapy to pharmacotherapy alone. While the intervention group needed less medication, they still benefited from medication in this study.

“But to the extent that the negative results, with regard to cardiovascular event prevention, remain both surprising and disappointing, there is a fundamental explanation for them: too little, too late. What works for prevention may not always work nearly as well for treatment.”

This article’s overall point is not wrong–the Look AHEAD study doesn’t necessarily overturn the results of the DPP study, and an intervention may work for prevention but not treatment. (Remember when the protagonist’s mom in 50/50 wants to give him green tea? [relevant part starts at 1:50]) But there’s more to consider: how do the two studies compare in rigor? And what about the publishing bias towards positive findings? A study finding no effect of a lifestyle intervention on preventing diabetes isn’t going to be cited by “virtually every clinical and clinical research diabetes paper”. (See Ioannidis’ “Why Most Published Research Findings Are False”.)

In fact, although both the DPP and Look AHEAD were fairly rigorous studies involving thousands of participants, the DPP only lasted an average of three years of study per participant. A followup, DPPOS, looked at the longer-term benefits of the initial intervention; they were still present but attenuated. This suggests that, although DPP’s intervention is often described as “preventing” or as “preventing or delaying”, it would be more accurate to describe it as “delaying” diabetes. And delaying is great! But not only does “delaying” not fit into our black-and-white thinking that you’re either healthy or you’re not, nor into our moralizing “if you act right/repent of your wicked ways, you will be healthy forever until you peacefully die of old age at 100”, nor our related, just world theory-inspired “health is under your complete control and genetic factors are trivial”, it just doesn’t make as good a headline.

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