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What are the effects of avocado on metabolic syndrome, which is “a clustering of risk factors”—high blood sugars, high blood triglycerides, high blood pressure, and obesity—that sets you up for diabetes and heart disease? “Avocado consumption is associated with [not only] better diet quality and nutrient intake, [but] lower metabolic syndrome risk.” Avocado-eaters only had half the odds of metabolic syndrome.

The study was funded by the Avocado Board, though, so it’s especially important to dig into how they designed it. The data came from a snapshot-in-time, cross-sectional survey of about 17,500 people, who were asked if they had eaten any avocado in the last 24 hours on two separate occasions. Two percent said yes, and so, the health stats from the few hundred folks who reported they had eaten avocado recently were compared to the health stats of the 17,000 individuals who said they had not. And, the proportion of people with metabolic syndrome among the avocado group was only half that of the non-avocado group. And, they were slimmer too—significantly trimmer waists and lower body weight, despite no significant difference in caloric intake.

The authors treat this as some kind of mystery, but it was just how many calories they ate on the day of the surveys, not over time—though you could see how people could lose weight. Avocados, like all fruits, are mostly water, along with fiber, which have no calories at all. So, a schmear of cream cheese on a bagel would add more than twice as many calories as the same schmear of avocado. But, that brings up an important point. Maybe those who eat avocados just tend to have healthier diets in general. I mean, if you’re spreading avocado on your toast, maybe you’re spreading less butter or margarine.

And indeed, avocado-eaters also reported eating more fruits and vegetables in general, and less added sugar. No wonder they were healthier. It’s right there in the title: “Avocado consumption is associated with better diet quality.” So this is, in effect, saying that those who eat healthier are slimmer, and have a lower risk of disease. Well, duh. And, this could be in part because they were eating avocados, have nothing to do with the avocados, or even in spite of the avocados. You don’t know, until you put it to the test.

What is the effect of avocados on body weight? It’s evidently evident from some study that an avocado extract “caused a reduction in body weight,” but the study was on the body weight of rats, and it was an avocado-leaf extract. Who eats avocado leaves? Well, evidently, in Nigeria, an herbal remedy for high blood pressure is avocado-leaf tea. Oh, does it actually work? Researchers tried it out on some hypertensive patients, and it seems avocado leaves “have a toxic effect on the liver that could cause liver damage.” So yeah, I guess, technically, “it can be used in the treatment of hypertension”—but only if you don’t care about the pesky “hepatotoxicity.” Uh, no thanks.

Are there no human studies on avocado fruit and body weight? Well, evidently, there was a study 50 years ago, back in 1960, on avocados and cholesterol, in which “the subjects did not gain weight when…avocados were added to their…diet.” I did find a reference to the study in the California Avocado Society Yearbook, lamenting how difficult it is to “impress the housewife” as to all the unnamed benefits of avocados.

Now, it’s true that body weights didn’t change much after avocado feeding. But, they didn’t just add avocados to their diet; they substituted avocado for some of the animal fat they were eating. So, they like swapped out lard for avocado; no wonder there was no weight gain. Now, in one subject, they did just add the avocado. Started out at 154 pounds, and after three weeks of added avocado, no weight gain. Okay, so maybe avocado is so satiating—so satisfying—that when you add it to your diet, you just naturally end up eating less of other stuff. But, you don’t really know, until you put it to the test.

“A randomized [controlled] study to evaluate the effect of Hass avocado intake on…satiety…and subsequent [caloric] intake.” Adding half an avocado to a lunch meal did improve satisfaction and reduce hunger. But duh, yeah, they just added an extra 112 calories of food; of course, they felt less hungry. The question is: did they feel so much less hungry that during supper, they ate 112 calories less to compensate? And, the answer is: no. In fact, they didn’t eat significantly less at all.

What about over time? This study added an entire avocado to people’s daily diets for six weeks, and found no significant weight gain. So, they triumphantly claimed to “dispel…the myth that avocados are fattening.” But, this was like the lard study. Yeah, they added an avocado, but they removed the same amount of fat in the form of margarine, mayonnaise, and oil. Now, this is a healthy swap—removing junk and adding nutrition, adding fiber. But, if the calories in and out are the same, then no wonder no difference in body weight. In fact, one could have just as well concluded that avocados are as fattening as margarine, mayonnaise, and oil, if you’re eating the same amount of fat.

Maybe the housewife was unimpressed because she just knew a little something about proper study design.

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