No Sugar

Sugar in Your Food, Your Blood, and Your Exercise

Nature Metabolism scored big this week with PR for a study on blood sugar and exercise. The study looked at hyperglycemia and exercise training. With lots of attention on Twitter and in the news media, it scored in the 98th percentile for commanding public attention. But the attention it got didn’t line up very well with what the study actually showed.

Researchers found an association between impaired glucose tolerance and the human response to exercise training. But the reporting focused on diets. For example, the New York Times told us:

Eating a diet high in sugar and processed foods could dent our long-term health in part by changing how well our bodies respond to exercise.

No Diet, No Cause and Effect

These researchers studied both mice and humans. In both cases, the study was all about the relationship between blood sugar and the response to exercise. For the mouse studies, they studied a control group and two different groups of mice with insulin resistance. In one of those groups, it was due to a Western diet. For the other group, it was caused by a drug administered to damage beta cells of the pancreas.

In the study of humans, these researchers didn’t even look at diets. Just blood sugar.

So this was a study of blood sugar, not diet. It showed a correlation between impaired glucose metabolism and an impaired response to exercise. It showed nothing about diet and nothing about causality in humans.

But right now, sugar is the #1 villain in our diets – according to popular culture. So this study about sugar metabolism becomes a study of dietary sugar and scores on PR.

Equating Diet and Metabolism

Our diets certainly can influence our metabolic function. But it’s not a simple linear relationship.

For decades, the bad boy of nutrition was cholesterol. High blood cholesterol leads to heart disease, so we all thought it must be bad to eat food with too much cholesterol. After 40 on that track, expert advisors for dietary guidelines figured out that this logic was false. Thus, the 2015 dietary guidelines removed excess cholesterol from the dietary problem list.

Now we’ve moved on to sugar. In popular culture, the distinction between dietary sugar and blood sugar receives little attention. So it’s easy to turn a study of glucose metabolism and exercise into a story about how sugar in your diet can sabotage your exercise regimen.

But make no mistake. That does not add up to faithful reporting of scientific facts.

Click here for the study, here for an editorial about it, and here for the reporting from the New York Times.

No Sugar, photograph © Frank Busch / flickr

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July 31, 2020

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