If you think that a diet rich in raw fruit and veg is the healthiest option, think again. Lots of vegetables need cooking to release their nutrients.
A healthy diet needs to include a stack of fruit and veg. Increasingly, experts are recommending we try to eat 30 plants a week to maintain good gut health, while paper after paper confirms the crucial role that vegetables play in overall life expectancy (a 2019 study found that one in 12 cardiovascular deaths could be attributed to not eating enough vegetables).
Clearly, eating plants in any form is better than none at all. But if you’re after the most nutrients for your buck, then you might be interested to learn that some veg is more nutritious after it’s been baked, steamed or stir-fried. That’s often the opposite of the messages that get knocked around on social media, with certain influencers claiming that the only path to better health is to go raw.
For years, I thought that cooking veg destroys most of the nutrients. In fact, I went entirely raw vegan a few years ago in a bid to “optimise” my diet, and during lockdown, I tried to stick to the “raw before 4” principle (where you only eat uncooked food before 4pm – yes, I know it makes little sense). Spoiler alert: eating exclusively raw veg during the UK winter is about as miserable as it is misguided.
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Some fruit and veg, no doubt, is better for you as nature intended. And anyone who’s had to suffer the vegetal sludge that some pubs and elderly relatives serve up as a ‘healthy’ side dish may be tempted to stick with the raw stuff. But some plants are better for us when they’ve been lightly cooked. Here are just a few.
Tomatoes are richer in antioxidants when cooked for 30 minutes
If you prefer your tomatoes in a pasta sauce or pizza passata, you’ve got the right idea. Those little cherry tomatoes may be great for snacking, but it’s only by cooking tomatoes that you can increase the amount of lycopene (an antioxidant associated with a lower risk of heart disease and cancer) present. 30 minutes of cooking can lead to a 50% increase in lycopene content.
In fact, even tomato ketchup is richer in lycopene than fresh tomatoes; it typically contains between 9.9 and 13.44mg of the antioxidant per 100g, compared to uncooked tomatoes which have up to 7.44mg per 100g. That’s not to say that you should switch your fresh toms for a squirt of tomato sauce on your chips, but it does go to show just how potent they can become when heat is applied.
It’s also worth flagging that heating tomatoes can reduce their vitamin C content – so it’s probably worth eating a mix of raw and cooked tomatoes if you’re susceptible to colds.
Boil carrots whole for more vitamin A
Roast dinner and wintry soups aside, most of us probably eat carrots raw. But heating them up increases their beta-carotene content – a nutrient necessary for good vision and decent immunity. In fact, cooking them in their skins more than doubles their antioxidant power, says Laura Brown, senior lecturer in nutrition, food and health sciences at Teesside University.
Writing for The Conversation, she says that you’re best off cooking them whole before slicing to avoid nutrients escaping into the cooking water. Brown also warns against frying carrots, which can reduce their carotenoid contents.
Steaming spinach increases the amount of calcium
Buy a bag of spinach to eat raw and it’ll see you through umpteen meals; cook it, however, and a bag will make about a teaspoon of green sludge. Cooking spinach not only maintains its levels of vitamin B9, but it also makes the calcium more bioavailable to us –important if you’re dairy-free.
However, if it’s antioxidants you’re looking for, having your spinach chopped and raw may be your best option. According to a 2019 study published in the journal Food Chemistry, raw baby spinach is richer in the antioxidant lutein than cooked. In fact, scientists found that lutein levels dropped by 40% after just four minutes of boiling, and by 50% after four minutes of steaming. Researchers concluded that a really good way of consuming spinach was to liquidise it, ie adding a handful of the raw stuff to smoothies.
Roast peppers for better immunity
Another salad staple, you actually get the most of your red pepper when you cook it up so that the immune-boosting antioxidants are easier absorbed. As with tomatoes, you’re better off roasting or stir-frying rather than boiling or steaming, as vitamin C gets lost when cooked in water. So, think about adding peppers to your stir-fries and fajitas or making a good old veg tray bake.
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Steam kale to make it more bioavailable
Who doesn’t love a gently massaged kale salad? While there’s nothing wrong with dousing a handful in olive oil and lemon juice and having it raw, it’s actually healthiest when lightly steamed. That’s because, Brown explains, it contains high levels of goitrogens (a kind of enzyme), which can interfere with iodine absorption – something you need for the production of thyroid hormones. While you’d probably need to eat a lot of raw kale to experience any negative side effects, we do know that cooking the stuff deactivates those enzymes. So if you have thyroid issues, you’re better off cooking your kale.
You want to be careful with how you cook kale, however. Cook for too long or in too much water and you’ll risk losing nutrients, so steam for a very short period of time, or throw into your stir-fries at the last minute.
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