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I’ve made videos on how not to die from heart disease, how not to die from cancer, how not to die from other deadly diseases like diabetes, but some of the most popular videos on the site are like …“the best way to cook sweet potatoes.”

All right, then. What’s the best way to cook bell peppers? Here’s the antioxidant power of raw green peppers and red peppers, and microwaving or stir-frying doesn’t seem to do much, though with boiling, there’s a drop. But then, if you measure the antioxidant activity of the leftover boiling water, the antioxidants weren’t destroyed, but just leached out into the cooking water. So, the researcher’s conclusion is that it’s “vital to consume the water used for boiling, in addition to the peppers, as bioactive compounds will be [left over] in the water.” But that’s not the take-away I get from this study. Drink the water or not, red peppers have nearly twice the antioxidant power of green, no matter what you do. So, while both peppers are, by definition, green-light foods, the red peppers, ironically, are even greener.

What about mushrooms? Probably best not to eat them raw, but what’s the best way to cook them? “Since cooking techniques clearly influence the nutritional attributes of mushrooms, the proper selection of [cooking method may be a] key factor to prevent or reduce nutritional losses. And…”microwaving and grilling were established as the best processes to maintain the nutritional profile of mushrooms.” For example, a significant decrease was detected in the antioxidant activity of mushrooms, especially after boiling and frying, while grilled and microwaved mushrooms reached in some cases higher antioxidant activity.

Boiling had a similar negative impact on the antioxidant power of cauliflower, which serves as just kind of a rough proxy for how many phytonutrients of potential benefit we might be losing. Blanching was better, where the cauliflower here was dunked into boiling water for three minutes and then run under cold water to stop it from cooking. I had never heard of steam blanching, but same idea. Steam for three minutes, then cool off, which appears to be better, since you’re not immersing it in water. Though, note there’s not much difference between steaming for six minutes and steaming for three, and then running under cold water. Too bad they didn’t look at roasting—that’s how you make cauliflower taste good. In fact, I’ve got two recipes on roasted cauliflower in my How Not to Die Cookbook (for which all my proceeds go to charity, of course).

There are certain antioxidants we’re especially interested in, though. Like the eyesight and brain-protecting green vegetable compound lutein. Here’s the back of the eyeball. What lutein does is protect those sensitive light-sensing nerves by blocking the high-energy blue light rays, which helps us see better, and may help us think better too. So, researchers looked at the effects of four different cooking methods on lutein concentrations. The first thing you’ll notice is that broccoli has like 50 times more than cauliflower—not a surprise, since lutein is a plant pigment, and cauliflower is too white. Here is it graphically, so you can appreciate the difference.

Then they compared boiling, steaming, microwaving, and sous vide cooking, which is like a fancy name for boiling in a plastic bag. And, boiling actually made lutein levels go up! How is that possible? Heat can actually disrupt the cell walls, and all the little subcellular compartments that can enhance the release of antioxidant compounds. Sous vide was similar; microwaving detrimental, at least for the broccoli, and… steaming the superstar, nearly doubling lutein levels.

Heat isn’t the only way to liberate lutein from greens. If you finely chop spinach, you can double the amount of lutein released during digestion in this experimental model. And make a green smoothie, or pesto, or some kind of puréed spinach dish, and you may triple the bioavailability. But you have to watch the heat. Steaming or boiling is one thing, but super high heat, like stir-frying, can reduce lutein levels to nearly nothing.

Frying is also bad for the purple pigments in blue potatoes—even air-frying; they just seem sensitive to extremely high heat. These special antioxidant plant pigments appear to be sensitive to really high temperatures; so, we should try to avoid frying, especially deep frying. That was one of the conclusions of an expert panel on cooking methods: avoid deep frying foods. Not only the nutrient losses, but all the added oil—not to mention the production of some toxic compounds at those temperatures. So, that continues to be a challenge to the food industry. What’s their solution? Forget deep-fat frying, let’s try frying in pure molten sugar. It’s like the SnackWell cookie phenomenon taken to its logical conclusion. Oh, you want low-fat? We’ll fry in sugar.

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