There is a lot of information out there about the best foods to help us lose weight, prevent cancer, fight inflammation – the list goes on. In fact, for everything about our health we try and improve, there’s someone with a new theory on how to do it. But what does the science say?
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to give you the evidence-based approach to take the mystery out of the best way to live a healthier, longer life.
Today’s show is all about that melt-in-your-mouth fruit you spread on toast. And no, I’m not talking about jam. I’m talking about the ever-popular Avocado. Can avocado lower our cholesterol as well as other whole-food fat sources such as nuts, or is it just avocado industry spin?
If you look at Avocado Board-sponsored reviews, they like to brag that “avocados are the richest known fruit source of phytosterols,” which are cholesterol-lowering nutrients found in plant foods. The operative word, though, is fruit.
Yes, there are more phytosterols in avocados compared to other fruit, but the reason that’s such a misleading statement is that phytosterols are fat-soluble substances; most other fruits hardly have any fat in them at all. So, of course, avocados are going to come out on top, compared to other fruit. But, let’s compare phytosterol content of avocados to nuts and seeds. One avocado has about a hundred milligrams of phytosterols. But, on the same scale, sesame seeds and tahini have 400; pistachios, pumpkin seeds, and sunflower seeds have about 300; and almonds and almond butter, flax seeds, and macadamia nuts have around 200. Even chocolate has about twice as many phytosterols as avocados.
Even though nuts and seeds have the highest levels overall, the studies that have been done on lowering cholesterol, lowering LDL (bad cholesterol) with phytosterols have used supplements, starting at 600mg up into the thousands. So, yeah, you can lower LDL cholesterol about 8% at up around 2,100 milligrams, but that would be twenty avocados a day. That would also be a lot of nuts. But, you can get an 8% drop in LDL just eating a palmful of nuts a day, a single ounce.
So, phytosterols are not the only components of nuts responsible for driving down cholesterol; there must be other components in nuts like maybe the fiber, or other phytonutrients that are contributing to the cholesterol-lowering effects. Hmm, I wonder if avocados have such components, too? You don’t know, until you put it to the test.
There are studies dating back more than a half century that appear to show that if you add an avocado to people’s daily diets, their cholesterol drops, and then goes back up when you remove the avocados, then goes back down again. Pretty convincing data until you see how the study was done. They didn’t just add an avocado, they swapped out animal fat. No wonder their cholesterol went down! And, that’s what nearly all avocado cholesterol studies are like.
Ten studies involving hundreds of people, and put them all together. And, it looks like adding avocados led to a significant drop in cholesterol and triglycerides, an average of about a 17-point drop in bad cholesterol. But, these were nearly all strictly substitution studies, where they removed saturated fat from people’s diets, and substituted in avocados. Well, of course, if you cut down on saturated animal fat, your cholesterol is going to drop.
You can tell this review was not funded by the avocado industry, because they point this out: “it is important to note that substituting avocados for saturated dietary fats as opposed to adding avocado to an already established baseline diet poses the greatest benefit.” Just adding avocado may confer no cholesterol benefits at all.
So, yeah, the avocado industry is right in saying that avocados are “a healthy substitute for butter/margarine, cheese, and cream cheese”, but that’s a pretty low bar.
Finally today we look at how whole plant sources of sugar and fat can ameliorate some of the inflammation caused by the consumption of refined carbohydrates and meat.
We saw how adding even steamed skinless chicken breast can exacerbate the insulin spike from white rice, but fish may be worse, closer to doughnut territory. But, what would happen if you added some tuna fish? You get twice the insulin spike. Same with white-flour spaghetti, and white-flour spaghetti with meat. The addition of animal protein may make the pancreas work twice as hard.
You can do it with straight sugar water. If you do like a glucose challenge test to test for diabetes, where you drink a certain amount of sugar, just adding a little meat to carbs doesn’t seem to do much, but once you get up to like a third of a chicken’s breast worth, you can elicit a significantly increased surge of insulin.
So, a chicken sandwich may aggravate the metabolic harm of the refined carb white bread it’s on. But, what about a PB&J? Well, we saw that adding nuts to Wonder Bread actually calms the insulin and blood sugar response. What if, instead, you smeared on an all-fruit strawberry jam? Berries have even more antioxidants than nuts, and can, indeed, squelch the oxidation of cholesterol in response to a typical American breakfast, and even reduce the amount of fat in your blood after the meal. And, with less oxidation, there is less inflammation when berries are added to a meal.
So, a whole plant food source of sugar can decrease inflammation in response to an “inflammatory stressor” meal. What about a whole plant food source of fat? If you eat a burger with a half an avocado on top, within hours, the level of an inflammatory biomarker goes up in your blood, but not as high as eating the burger without the avocado. This may be because all whole plant foods contain antioxidants, which decrease inflammation, as well as fiber, which is one reason even high-fat whole plant foods, like nuts, can lower cholesterol. And, the same could be said for avocados. Significant drop in cholesterol levels, especially in those with high cholesterol, with even a drop in triglycerides.
If eating berries with a meal decreases inflammation, what about drinking berries? Sipping wine with your white bread significantly blunts the blood sugar spike from the bread, but the alcohol increases the fat in the blood by about the same amount.
The healthiest approach is a whole food plant-based diet, but there are “promising pharmacologic approaches to the normalization” of high blood sugars and fat by taking medications. “However, resorting to drug therapy for an epidemic caused by a maladaptive diet is less rational than simply realigning our eating habits with our physiological needs.”
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