Thursday, October 29, 2020

Potatoes: Another Stupid Study

"People with type 2 diabetes need not avoid eating potatoes based on glycemic index" is the title of a recent Eurekalert news release about potatoes. Now, most people seeing that would think "I don't need to avoid potatoes" and wouldn't read the rest of the story.

Note that the study was funded by the Alliance for Potato Research and Education (APRE), and although they say APRE had no role in designing or carrying out the study, one tends to be biased toward any group that is sponsoring one's work. APRE "is a not-for-profit organization 100% dedicated to expanding and translating scientific research into evidence-based policy and education initiatives that recognize the role of all forms of the potato—a nutritious vegetable—in promoting health for all age groups." That certainly doesn't sound unbiased.

However, even more important that the funder for this study is what they actually showed. They showed that participants had a better 'nocturnal' glycemic response when they ate a mixed meal with skinless white potatoes compared to an isoenergetic and macronutrient-matched mixed meal that included a low glycemic index carbohydrate food -- basmati rice. 

Note that they didn't compare potatoes with a no-starch meal, say substituting broccoli or spinach for the potatoes. They just say potatoes aren't worse than basmati rice. But I suspect some people, even dieticians, will remember "People with type 2 diabetes need not avoid eating potatoes" and eat baked potatoes or even french fries when they would have much better control if they ate green vegetables instead. 

Participants ate about 50 grams of carbohydrate per meal, the same amount that is used to measure glycemic index.

 I agree with the authors that the glycemic index alone isn't enough to predict the glycemic impact of a mixed meal. And even with the exact same meal, different people will have different responses. Even one person may have a different response on a different day. We have to test ourselves, preferably with a continuous glucose monitor, to find out how various foods and mixed meals affect us.

However, no one with type 2 diabetes should be eating 50 grams of carbohydrate per meal. Unless money is really tight and we need to fill up on cheap starches, when potatoes would be better than cake and cookies, I think the potatoes should remain at the grocery store. And people who write research press releases should be clearer about exactly what their research shows.

The full text of the study can be found here.

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