An Avocado A Day Is No Panacea

There are many circular stories in the medical media world that are extremely irritating to me. Every 3-6 months we have a scare about artificial sweeteners and it’s almost always a non-event. The Environmental Working Group regularly puts out misleading press releases making a huge deal out of barely-detectable residues of heavy metals in some consumer product. Someone, somewhere, is already writing an article about how alcohol is secretly good for you for some obscure and unconvincing reason.

But not all circularity is annoying. My favourite thing is when food producers get together and run studies trying to prove that their produce is healthy. I’ve covered Big Blueberry numerous times—they fund at least one study a year trying to show that blueberries can save your life. I’ve seen Big Kimchi, the literal secretive government entity trying to get you to buy more kimchi, Big Walnut, and even Big Pasta. It’s always a fun story to tell.

The latest in the round of Big Food is Big Avocado. If you believe the news, avocados may be the secret to improving your heart health and not dying of a stroke. In reality, the data doesn’t show much of a benefit for the vegetable at all.

The newest study is an analysis based on the Habitual diet and Avocado Trial (HAT, because everything needs a fun acronym). The HAT study randomized people to either get 6 months of nothing—eating their normal diet—or to get an avocado per day. Most of the people in the avocado group ate their avocados on schedule for the study period. At the end of the study, the researchers looked at various measures of heart health, in particular cholesterol levels.

The new paper looked specifically at different types of cholesterol molecules. We tend to say cholesterol as a single entity, but it’s really divided up into various different types—good, bad, etc—and then further subdivided into some quite specific categories. In this study, the authors found that an avocado a day reduced the total amount of low density lipoprotein (LDL) particles in people’s blood by around 2% over the course of the 6 months. This is bad cholesterol that is known to cause heart attacks, and so a fall is generally seen as a good thing, although given that statins reduce LDL by around 50% it’s not a particularly impressive reduction.

There were no changes, however, in any other kind of cholesterol. No increase in good cholesterol, no modification of triglycerides, nothing. There weren’t even changes in the specific subtypes of LDL, which was sort of the entire point of this article. So at best it’s a modest improvement in one type of cholesterol that may or may not be related to long-term heart health.

But that’s not the real issue. The bigger problem is that this is just a substudy based on the original trial. The original HAT paper came out in 2022, and found no benefits on any of the primary outcomes including weight loss, fat loss, blood pressure, blood sugar, or quality of life. So avocados don’t improve heart health based on most of the pre-specified outcomes that the authors thought were important before they started the trial.

The entire point of the new paper was to see if the modest reduction in LDL cholesterol seen in the 2022 paper also caused changes in the subtypes of LDL particles which are categorized by size (small, medium, large). This is important because the different sizes of LDL particles are thought to have different risks when it comes to heart health, so a small overall reduction in LDL might be very impactful if it is also causing a huge reduction in a specific subtype of LDL particle. But the paper found no differences in LDL subtypes by avocado consumption, and indeed no other improvements in any other measure of cholesterol.

In other words, this is a total nothing of a finding. They repeated a secondary analysis from their 2022 paper and found the same result, with all of the additional analyses showing no benefits for avocados.

The original 2022 HAT study is a fairly robust, impressive piece of research. The authors convincingly showed, in a randomized sample of 1,008 people, that avocados have no benefits for heart health on most of the metrics that we use.

There was a modest benefit in LDL cholesterol specifically. Given the number of things that the authors were measuring, it’s not unlikely that this is a statistical quirk, but it’s possible that eating an avocado a day may improve your LDL a bit. It’s unclear if a 2% reduction is enough to actually improve your health, but it’s not nothing.

The new study adds nothing to that discussion. Given the fairly comprehensively null findings of the HAT trial, I think it’s fair to say that eating an avocado a day almost certainly won’t stop you from having a heart attack.

That’s not a reason to avoid avocados. They’re still a delicious food with an important place in a good brunch plate. But despite the efforts of Big Avocado, they probably don’t improve your heart health.