If anyone still cares about nutritional epidemiology, perhaps we should talk about FIBER, since there's a brand spanking new study showing high-fiber diets are associated with less breast cancer risk.

But there's a special problem with studying fiber. https://acsjournals.onlinelibrary.wiley.com/doi/abs/10.1002/cncr.32816

If you had to pick one thing that was a marker for a healthful diet, I'd go with fiber, since you get it in the most nutritious foods - veg, fruit, whole grains, legumes.

(As an aside, the thing that's a marker for the worst diets is bacon.)

So diets high in fiber are ALWAYS high in other good things and studies that look at high-fiber diets and health outcomes pretty often find that those diets correlate with lower risk. BUT!

You have no way to figure out if it's the fiber or the other good things. Sure, it's reasonable to suspect that fiber is good -- gut health and all. But really we don't know. There's only one way to find out - a controlled trial with fiber SUPPLEMENTS.

There aren't very many of those. I went to Pubmed and searched "cancer fiber supplement" clinical trials and got this, showing fiber supplements don't decrease the recurrence of colorectal adenoma, but not much more. If you have others, send 'em! https://www.ncbi.nlm.nih.gov/pubmed/10770980 

In general, trials with fiber SUPPLEMENTS are meh. There are some benefits - supplementation does seem to lower cholesterol, and it's reasonable to conclude (I have) that fiber is generally good for you. https://www.ncbi.nlm.nih.gov/pubmed/27724985 

To sum up, fiber's probably good, but epi studies of high fiber diets and different health outcomes are likely to be hopelessly confounded by the other good things in high-fiber foods and the health habits of people who eat them.

We now return to our regular COVID programming.