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Issue #62 (December 2019)

From the Editor

We don’t see huge effects in a lot of the studies that we cover in the NERD. Which is why it’s pretty surprising that this issue reviews a couple of meta-analyses that found really large impacts. However, I hold the conclusions from one of these meta-analyses much more lightly than the other.

The first meta-analysis I’d like to discuss took a look at the long-term efficacy of lifestyle interventions to prevent type 2 diabetes in people at high risk for developing it. After scouring the literature for clinical trials studying the issue, the researchers found seven trials that lasted at least a year. The trials all involved some kind of calorie reduction or fat-loss program coupled with increased physical activity. Some (but not all) of the studies also encouraged decreasing saturated fat intake. The physical activity leaned toward mild intensity in many of the studies, involving things like increasing time spent walking.

The main take-away from the study is that these lifestyle modifications cut the risk of developing diabetes by close to 50%. That’s a big impact that can dramatically improve the quality of life, if not downright save lives, for a lot of people. While “move more, eat less” is easier said than done, this study makes it clear that it’s really worth the effort for people at risk of diabetes.

While I think this study’s results are a big deal, I can’t say that I find them too surprising. It puts a number on how effective lifestyle changes can be in preventing diabetes, but the fact that weight loss coupled with increased activity works well isn’t exactly breaking news.

However, the results of another meta-analysis we look at in this issue were a bit more surprising to me. The meta-analysis examined the effect of curcumin supplementation on depression, and found a large impact on reducing depressive symptoms, and an even bigger impact on symptoms of co-occurring anxiety in people with depression who were mostly on concurrent antidepressant therapy.

Based on what we know about oxidation and inflammation’s possible role in depression, it’s plausible that curcumin could possibly be a useful adjunct in depression. But I wouldn’t expect it to have as large of an impact as was found here. While this meta-analysis provides a very good reason to researchers to conduct better, longer trials looking into curcumin’s efficacy in depression, I don’t take this meta-analysis’ results at face value for several reasons. I’ll briefly mention two.

First, the trials that went into this meta-analysis are all pretty short term and small, which are exactly the kinds of trials I’d expect to inflate effect size. Second, the meta-analysis didn’t report on possible publication bias, leaving open the possibility that these small, short trials that got positive results are the ones that end up getting published and put into meta-analyses, while the less flattering ones are stuck in file drawers.

While I’m not quite convinced that curcumin has the impact on depression that the meta-analysis says it does, I’m excited to see more research on this topic since if the real effect size is anywhere close to what this meta-analysis found, it’d be a really big deal.

Gregory Lopez, MA, PharmD
Editor-in-chief, Nutrition Examination Research Digest

See other articles in Issue #62 (December 2019) of Study Deep Dives.