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Issue #46 (August 2018)

From the Editor

Volume 1

One of the reasons you read the NERD is probably because you’re looking for an unbiased, but in-depth, review of recent evidence about nutrition. Summarizing the evidence that’s out there is pretty much Examine.com’s raison d'être. However, we may have outdone ourselves in reviewing the evidence in this volume, where we review a review of reviews of the evidence.

That’s pretty meta, so feel free to take a moment.

The, er… review I’m talking about concerns melatonin, which is a pretty well-studied molecule that may have more uses than just for sleep. Part of this idea is evident from the fact that it’s not just humans who make melatonin — even some bacteria and plants synthesize the stuff, so it’s clearly not just there to tell them that it’s time to stop watching Netflix and go to bed! But it still may impact aspects of their circadian rhythms, even if it doesn’t tell them that it’s time to close the laptop. For instance, some gut bacteria seem to respond behaviorally to melatonin, which opens up the interesting possibility that our circadian rhythms could influence our microbiome. Plants may use melatonin to regulate reproductive rhythms, regulate growth, and also as an antioxidant.

Melatonin’s antioxidant properties may also be useful for human disease as well. And, as we briefly state in our article, circadian rhythm problems may also lead to inflammatory issues and could contribute to diseases like hardening of the arteries. If melatonin can help circadian rhythms get back on track, it could also possibly play a preventive role in disease.

While melatonin could do a heck of a lot, the only question that really matters in terms of health is what it actually does. The melatonin study that we cover in this volume attempts to find out what the science says by systematically searching the literature for reviews of melatonin’s effects in humans, as well as in animals and test tubes, and summarizing the state of the evidence.

In other words, it’s an “umbrella review” — a review of reviews. Umbrella reviews are a useful way to answer broad questions for a topic for which a lot of research has been done. The umbrella review we cover in this volume examines a single molecule (melatonin) and looks at the evidence for its possible effects by searching for and summarizing reviews on the topic. However, umbrella reviews can also work the other way around: you can ask what works for a single outcome and search for reviews of all the things that have been tested.

So, now that you’ve read a summary of a review that reviews a review of reviews, on to the research!

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

Volume 2

Sometimes when you want to know the answer to a practical question concerning nutrition, it’s a better idea to hit up individual clinical trials rather than meta-analyses.

Why would one want to do this? Well, one of the main purposes of standard meta-analyses is to pool small studies together to get a larger sample size. This shrinks the error around effect estimates, and allows you to come up with more precise estimates of the effect size (assuming there are any). In the process, you can also make sense of conflicting study results, since sometimes the conflict is just a result of statistical noise, which meta-analyses (ideally) help to reduce.

But sometimes the interventions in the individual studies are pretty different from one another. Other times, the populations being studied are different. And occasionally the measures used to examine the efficacy of the intervention can be quite different. All three of these reasons may be the case more often in nutrition than in some other areas of the health sciences. And if any of these conditions hold, it may be better to look at an individual study that is closest to the specific intervention, population, and outcome that you care about rather than look at the synthesized results of a meta-analysis, which can add noise to the particular situation you’re concerned with.

In this volume of the ERD, we cover one meta-analysis that meets all three of the above criteria concerning chocolate milk’s effects on exercise recovery. It examines studies that use several different kinds of exercises and populations, fitting the first and second criteria. The meta-analysis also meets the third criterion because the different studies all measure different things concerning “recovery” for the most part. There is quite a bit of overlap, of course — otherwise, no meta-analysis would be possible. However, the measurements that do overlap are mostly things which don’t have the strongest practical implications; in other words, they’re surrogate markers for the outcomes most people actually care about. This makes sense if you think about it, since what most people would care about in terms of recovering from a bout of training is how well you’d perform in the next bout. But “performance” means different things in judo than it does in cycling. So a judo practitioner would probably do better to look at the single study done in this meta-analysis rather than the meta-analytic results themselves if they’re curious about how chocolate milk affects recovery in their sport. If they did, they would find that chocolate milk did seem to improve one of the more judo-specific outcomes measured in that study (the Special Judo Fitness Test).

None of this means that the meta-analysis isn’t at all useful; it provides an evaluation of chocolate milk’s effects (or, as you’ll see, lack thereof) on some common measurements that are more sports-neutral. It’s just that if you happen to have a specific thing you care about, sometimes it’s better to look at references that most match the circumstances that concern you, even if you sacrifice statistical power in the process.

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

See other articles in Issue #46 (August 2018) of Study Deep Dives.