More Veggies, Less Heart Disease? Not Exactly

In this moment, food policy advocates are in love with plant-based diets. Many reasons do favor plant-based diets. In fact, the advice to eat more vegetables has been dispensed at family tables for generations. The American Heart Association promotes eating more veggies for cutting heart disease risk with great enthusiasm.

But today, a new study suggests the enthusiasm might be a bit over the top. Most of the association between vegetable intake and heart health may well be due to residual confounding, say this authors of this study. It is a potent reminder that correlation does not equal a cause and effect relationship.

Consume Observational Data Cautiously

Let’s start with an obvious fact. This new study is observational. So it has the same limitations as all of the observational studies that came before it on this subject. It uses self-reported data on vegetable intake from the UK Biobank cohort of 399,586 persons. But it is a robust observational study that takes a hard look at the issue of residual confounding. The authors conclude:

“Higher intakes of raw, but not cooked, vegetables were associated with lower CVD risk. Residual confounding is likely to account for much, if not all, of the observed associations. This study suggests the need to reappraise the evidence on the burden of CVD disease attributable to low vegetable intake in the high-income populations.”

The bottom line here is actually quite simple. In their zeal to promote consumption of vegetables and plant-based diets, folks like the American Heart Association might be overstating the benefits.

Though veggies are great, they don’t offer a medical miracle for heart health

But Do Eat Your Veggies

Of course, the folks who have been urging us to eat our vegetables have plenty to say about this. For example, Professor Naveed Sattar at the University of Glasgow says there’s plenty of good evidence for the benefits of vegetables in reducing risk factors for heart disease.  “The authors may have over adjusted for factors that account for lower intake of vegetables,” he cautions.

Another view comes from nutrition scientist Alice Lichtenstein, who tells CNN:

“The results are not surprising. Picking out one single component and assuming just adding it to the diet, e.g., vegetables, is not likely to result in the desired effect. One thing that has become clear over the past decade is we should not be looking at single foods or nutrients, rather the whole dietary pattern.”

In other words, keep eating your veggies, but don’t expect that to magically reduce your risk of heart disease. It’s the whole pattern of what you eat that influences your health risks.

Click here for the study, here for more from the investigators, and here for further reporting. For additional perspective, click here.

Pythagoras Advocating Vegetarianism, painting by Frans Snyders / WikiArt

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February 21, 2022