Yesterday, salt was bad for you, but today it’s just fine. Multiply these findings by a hundred and you have the confounding noise that passes for research in most nutritional studies. What the heck is going on?
The problem is, human dietary studies are hard. Most of them depend on people recalling what they ate over the last few weeks, and the combination of forgetfulness and the desire to look good makes the data suspicious. A truly randomized, controlled trial needs to take place in some kind of uber-regimented locked-down facility that even college volunteers wouldn’t appreciate. This is why many of these studies are done with mice and rats.
There’s another way, and it’s called a meta-analysis: a mathematical technique that combines multiple studies to wring the most out of all of them. Meta-analyses have their own issues, mainly because studies need to be well-matched to combine them. But they provide a way to create data sets with larger populations and potentially greater power.
So it has been reassuring to see studies like this recent Chinese meta-analysis of over 700 people demonstrating that probiotic consumption is indeed associated with reduced measures of anxiety. The researchers point out that there were conflicting data, but overall, the results were significant. With over 350 million people in the world afflicted with anxiety and depression, studies like this provide some hope.