More Avocados Equal Less Diabetes? Not Really

If you pay attention to nutrition headlines in consumer media, avocados sound pretty amazing. “Eating more avocados could help women stave off type 2 diabetes,” says one report. “Avocado a day may keep diabetes at bay,” says another. The only problem is that neither of the studies that prompted those stories actually support the claims they’re making.

Both studies are cross-sectional and observational. They document an association between avocado consumption and type 2 diabetes. But as both papers state clearly, these studies cannot support a causal inference. Does eating avocados make a person healthy? Or do healthy persons eat avocados to prove they have earned their good health? Or do healthier people eat avocados for an assortment of other obscure reasons? These are all possibilities.

What is unlikely is that avocados have sufficient metabolic effects all by themselves to prevent diabetes in a very meaningful way. The avocado is a wonderful, tasty fruit, but it is neither magical or medicinal.

Mexican Health and Nutrition Survey

The most recent of these studies used records from 25,640 participants in the Mexican Health and Nutrition Survey. Researchers found an association of self-reported avocado consumption with a 21% lower risk of type 2 diabetes in women, but no difference in men. The authors are quite clear that they cannot rule out residual confounding and that the cross-sectional nature of their study “cannot establish causation.”

Metabolomic Biomarkers of Avocado Intake

The Journal of Nutrition published the other study generating headlines in October and it’s interesting because it used metabolomic markers for avocado intake. In other words, the researchers did not rely on self-report alone. They looked for biological artifacts of avocado consumption to indicate that subjects counted as consuming the fruit really were consuming it. They did not have to rely on self-reports. This made the findings stronger, but still, the observational study design “precludes causal inferences.” So no, this study does not prove that avocados “keep diabetes at bay.”

Health Claims Are Really Marketing Claims

Avocados are great. We love our guacamole and our avocado toast. In moderation, they can be part of a healthy dietary pattern. But context is everything and health claims often represent permission for excessive consumption. The Hass Avocado Board supported these studies because they want to sell more avocados. They are marketing tools.

This doesn’t mean the studies are bad, but we are not fans of the puffery that grows out of them. Puffery is not good for dietary health.

Click here for the study of Mexican Health and Nutrition Survey data, and here for the study of metabolomic data. For the puffed-up news reports, click here and here.

Avocado Toast, photograph by Nicole De Khors, licensed under CC BY 2.5

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May 1, 2024