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Vegetables: Cooked or Raw?

September 23, 2020
steamed vegetables

You’ve heard it your whole life: Eat your veggies. From your childhood dinner table to the latest fad diets, the health of veggies has never been in question.  And for good reason! Increased vegetable intake is associated with lower risk of chronic disease and a number of cancers, including prostate cancer. Almost all vegetables, cooked or raw, contain an array of vitamins, other nutrients, and immune-boosting fiber for your microbiome.

But what’s the best way to eat vegetables, raw or cooked? You may have heard lots of armchair opinions on this. Is there a “best way” to way to prepare vegetables and/or cook vegetables, and are you killing or reducing the “good stuff” when you cook them?  The answer is: it depends.

Although nutrient loss following the cooking of vegetables has gotten a lot of attention, it turns out that many vegetables provide more bioavailable nutrients after being cooked. This includes cruciferous vegetables like cabbage and broccoli, and one other prostate favorite: tomatoes. Technically a fruit, tomatoes are generally healthy eaten raw, but cooking them in extra-virgin olive oil gives tomatoes a health boost. The added heat works alongside the olive oil to assist in the absorption of lycopene, a powerful carotenoid that is responsible for the tomato’s antioxidant capability as well as its bright red color. Interestingly, lycopene accumulates in prostate tissue – all the better to do its cancer-fighting work – which may partially explain why eating tomato products may be associated with a lower risk of lethal prostate cancer.

On the other hand, there are certain nutrients, such as vitamins C and B1 (thiamine), as well as some polyphenols (antioxidants) that are easily destroyed when exposed to heat. For example, one study found that most common cooking techniques lowered the vitamin C content in several different types of vegetables.

So if you are going to cook vegetables, how should you do it? Science has pointed out that boiling may be one of the worst options, since many water-soluble vitamins and antioxidants are leached out from the vegetable and into the water that’s left behind. But it’s not just the water-soluble vitamins that get destroyed in boiling. Let’s use broccoli as an example. Broccoli and other cruciferous vegetables are high in beneficial glucosinolates. In order for your body to access the good stuff in the glucosinolates, it needs the aid of a helper enzyme that also exists inside the broccoli. If you chop or chew raw broccoli, it releases the helper enzyme from the broccoli cells. On the other hand, if you overcook your broccoli with excessive boiling, the helper enzyme is destroyed. Light cooking, such as steaming, is the perfect blend that preserves both the enzyme and the glucosinolates.

Steaming vegetables may be the cooking gold standard in terms of both preserving and enhancing nutritional value. There’s minimal water added, and while a few nutrients may be destroyed in the heating process, you typically maintain the micronutrient profile, especially with cruciferous vegetables. Roasting and grilling vegetables is also an option. Unlike grilled meat, grilled vegetables do not contain the same potentially harmful compounds (e.g., HCAs) that have been indicated in animal studies to be carcinogenic. And last but not least, while microwaving may be safe to your food, it can cause substantial culinary damage if not done carefully – resulting in soggy and unevenly heated product. While a well-functioning microwave is safe to use, remember that microwave radiation has the same effect on humans as food, so a malfunctioning or ill-closed device can leak radiation. It’s temptingly easy to reheat leftovers in plastic containers, but many types of plastic leach hormone-disrupting chemicals (such as phthalates) into the food when microwaved. Follow standard operating procedures and stand a few feet away from the machine while it’s in operation.

There is a lot of science focused on vegetables and cooking, and it can be easy to get lost in the details. Here’s a great principle to not overthink it: eat vegetables, however you like them. Don’t let the details distract you from incorporating vegetables, one of the healthiest foods on the planet, into your diet. Instead, focus on what you’re pairing with these vegetables, and do your best to avoid cooking with processed sauces and high-fat ingredients. And one last tip: mind your vegetable prep. While Michelin 5-star restaurants might spend a lot of time peeling those unwanted skins and straining those unwanted seeds, microbiome science dictates exactly the opposite: more roughage is better. To maintain as much of the rough fiber as possible, you may consider buying organic so that you can eat the nutrient-dense peels and seeds that go along with all of nature’s richness.