Revisiting Some Thanksgiving Churnalism

A useless nutrition hack

It’s the Friday after Thanksgiving. I give thanks to everyone who is working; I am not. Still, if you need to use Sensible Medicine for a quick break from the family or shopping, I want to make sure there is something here. I am reposting an article from two years ago, a nice piece of nutrition churnalism that works perfectly for the holiday.

Today, I give thanks to the New York Times, the paper of record, for an article arguing that we would be healthier if we saved our carbohydrates for the days after Thanksgiving, after they had spent some time in the refrigerator.

On November 8^th, 2023, the Times published an article titled Pasta and Rice May Be Healthier as Leftovers. Here’s Why. The gist of the article was that resistant starches, those that are harder to digest and are present in whole grains, beans, nuts, and other foods, are better for us than regular starches, like those in rice, pasta, and the lovely, mashed potatoes that I hope you enjoyed yesterday. However, the article stated, regular starches can be made more resistant by cooling them.

Ok, this might seem too good to be true, so let’s think about where ideas like this come from.

To support the “resistant starch” benefit, the author cites a (somewhat irritating) review article. The mechanistic arguments in favor of resistant starches include lower postprandial glucose spikes and an “improved microbiome”. Diving into the literature, I found that the benefits of resistant starch have been studied mostly in small studies using surrogate endpoints. Fortunately, some good meta-analyses have been published (here, here, and here). The current evidence suggests that resistant starch lowers post-prandial sugars but has no effect on fasting plasma insulin, insulin sensitivity, acute insulin response, or other measures. It's probably not surprising that there is little to no evidence from controlled trials that a change to resistant starches improves clinical outcomes.

The author of the Times article cites one fascinating study. The CAPP-2 RCT randomized people with Lynch Syndrome to 30 grams of resistant starch daily or placebo for up to 4 years. The researchers then looked at long-term cancer outcomes 10 years later. There were no differences in colon cancer incidence (the outcome the authors expected to affect), but fewer participants randomized to resistant starch had non-colorectal Lynch Syndrome cancers (27 vs. 48; HR, 0.54; 0.33–0.86; P = 0.010).

The author of the NYT article makes the jump to equate resistant starch and fiber and then discusses the benefits of fiber. Resistant starch and insoluble fiber are different. In the colon, insoluble fibers pass unchanged while bacteria ferment resistant starches — hence the idea that resistant starch might have beneficial effects on the microbiome.

So, with that knowledge, let’s get to how the NYT article racks up the churnalistic sins. The obvious issue here is that the benefits of resistant starches over simple sugars are mainly based on observational and surrogate outcomes. The leap from these to actual clinical benefits — decreased mortality and improved quality of life — is always substantial. The extrapolation from a 20-year study of people at high risk for malignancy to you sitting in your kitchen the days after Thanksgiving is a huge one. Then there is the idea that this imagined benefit could be extrapolated to simple starches, maybe made a bit hardier by a night in the fridge, which is getting pretty extreme. It seems like our author has committed sin #1 — observational studies almost never prove causation — and sin #2 — extrapolation and generalization.

The conclusion? I hope you enjoyed some simple and complex carbohydrates — pecan pie, sweet potato pie, mashed potatoes, corn bread stuffing — right out of the oven. I hope you continue to enjoy cold leftovers out of the fridge or reheated in the coming days.

Photo Credit: You Le