Cutting Sugar Clears Up Liver Disease in Children?

JAMA grabbed some headlines this week on a popular subject – cutting sugar consumption for kids. Fatty liver disease is a serious problem and the headlines point to a simple solution. “To fight fatty liver, avoid sugary foods and drinks,” said the New York Times. How did researchers prove that? All it took was a randomized study of 40 adolescent boys. Half of them minimized their intake of free sugars while the other half continued with their usual diet. Fat in the liver (measured by MRI) declined significantly after just eight weeks.

Voilà! Investigators proved their point. Or did they?

Not So Fast

The authors themselves warn us to be cautious. We should think of these findings as “preliminary” until we have more definitive data. They list seven limitations of this study We definitely agree with their caution. But where we disagree is on the attribution of effects. Are they measuring the effect of less sugar? Or instead, is this effect the result of a whole range of improvements in the diet?

The fact is that diets are complex. The diets of these 40 boys have many moving parts. In the case of the boys getting the “low free sugar diets,” they got more than just less sugar. They got family meal plans designed by a registered dietitian. They got meals prepared for them and delivered to them. Those were meals for the entire family. Registered dietitians did the food prep.

It’s pretty clear that these families improved their diets overall. And it showed. Their weight and their BMI dropped. Blood pressure improved.

In the control group, researchers told subjects to keep eating what they always eat. Plus, they gave them gift cards for the grocery store. So they had more money to spend on food. The same food they were consuming when they developed fatty liver disease.

Confirming a Bias About Sugar

Researchers mounted this study to prove sugar restriction will reduce excess fat in boys with fatty liver disease. So when they found an effect, they attributed to the sugar restriction. It’s in the title of the study. It’s in the press release and all the headlines.

However, we would argue that this study tells us about the benefits of medical nutrition therapy more broadly. These boys benefited from individualized dietary plans by a registered dietitian. Part of that plan was less free sugar. That’s good. But along with that came the benefit of better food. They enjoyed the luxury of having nutrition professionals plan, prepare, and deliver meals designed just for them.

Does cutting back on sugar help? Probably. But perhaps more important is the whole of the diet these boys received. Obsessing about a single component of our diets can be misleading. We are what we eat and all of it matters.

Click here for the study, here for the press release, and here for reporting in the New York Times.

Liver Tissue, photograph © ZEISS Microscopy / flickr

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January 25, 2019