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Fruits and vegetables contain a lot of nutrients and antioxidants like carotenoids, flavonoids, and polyphenols that help prevent health issues like cancer and cardiovascular disease and can improve mood. Antioxidants help your body counteract damage caused by toxic byproducts called free radicals. Eating more fruits and vegetables also increases your vitamin C, vitamin A, vitamin B6, thiamine, and niacin, minerals, and fiber.
But it can be tricky to know how you should store and prepare fresh foods to get the most nutrients.
Luckily, when you store most fruits and vegetables, this generally does not affect antioxidants levels. In fact, antioxidant levels can even go up in the few days after you buy the fruits and vegetables. But when you start to see the fruit or vegetable spoil and turn brown, that usually means that they have started to lose antioxidants. The main exceptions are broccoli, bananas, and apricots, which are more sensitive and start to lose their antioxidants during storage within days, so eat those sooner than later.
Whether you should cook or eat raw fruits or vegetables to maximize antioxidants varies. Some vegetables like mushrooms, asparagus, cabbage, and peppers gain certain antioxidants after they are cooked.
1. Tomatoes: Cooked may be better than raw.
Storage tip: Even though this will make shelf life shorter, store tomatoes in room temperature since tomatoes can lose antioxidants (and flavor) when stored in cooler temperatures.
Cook your tomatoes to release higher levels of lycopene and total antioxidant activity. You can cook them for up to 30 minutes at 190.4 degrees Fahrenheit (88 degrees Celsius). Lycopene is found in red fruits and vegetables like watermelon, red bell pepper, and papaya and has been linked to lower rates of cancer.
Raw tomatoes have less overall antioxidants, but have more vitamin C.
2. Carrots: Cooked may be better than raw.
Cook your carrots to get more beta-carotene, an antioxidant that gets converted in your body to vitamin A, which is good for your eyes and immune system. Sous Vide carrots for best results. Steaming or boiling carrots preserves more antioxidants than roasting, frying or microwaving carrots. If you’re in Top Chef mode and want to maximize antioxidants, try sous vide carrots, which has even more antioxidants than steamed carrots.
3. Broccoli: Raw and cooked.
Storage tip: Keep broccoli wrapped in packaging in the refrigerator at 1 degree Celsius (or 33.8 degrees Fahrenheit). Unlike most vegetables, broccoli tends to lose antioxidants faster than other vegetables when stored without packaging, particularly when it starts to lose its color and turn yellow. Wrap the broccoli in microperforated or non-perforated packaging to keep antioxidants for longer.
If you eat raw broccoli, you'll get higher levels of an enzyme called myrosinase, which creates helpful compounds like sulforaphane, which blocks the growth of cancer cells and helps fight Helicobacter pylori, a bacteria responsible for stomach ulcers. Myrosinase is sensitive to heat and thus destroyed during cooking.
Cooked broccoli and other cruciferous vegetables like cauliflower, increases indole, which is thought to be protective against cancer. Steamed broccoli has also better potential to reduce cholesterol than raw broccoli.
Sous vide or steam broccoli to keep antioxidants and nutrients. Boiling 9-15 minutes causes the loss of up to 60 percent of nutritious compounds become leached into the water. Stir-frying and a combination of boiling and stir-frying (common in Chinese cuisine) causes the most loss of vitamin C and nutrients. Steaming allows broccoli to retain better color and texture.
4. Cauliflower: Raw and cooked.
Fresh cauliflower has 30 percent more protein and many different types of antioxidants such as quercetin. Raw cauliflower keeps the most antioxidants overall, but cooking cauliflower increases indole levels.
Don't boil cauliflower in water because that loses the most antioxidants. Water-boiling and blanching causes the worst loss of minerals and antioxidant compounds in cauliflower because many of the nutrients get leached into the water. Steam or sous vide cauliflower to maintain nutrients.
5. Brussel Sprouts, cabbage: Raw and steamed.
Brussel sprouts and cabbage are cruciferous vegetables rich in compounds protective for cancer. One study found that people who consumed about 300 grams or two-thirds pound of Brussels sprouts daily for a week had higher levels of a detox enzyme in the colon, which helps explain the link between eating cruciferous vegetables and lower risk of colorectal cancer.
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Raw Brussels sprouts give you the most folate and vitamin C. Steaming Brussels sprouts can release more indole compounds (but they arguably taste best when roasted!).
6. Kale: Raw and blanched.
Kale has beta-carotene, vitamin C, and polyphenols. Cooking kale significantly lowers vitamin C and overall antioxidants. Keep kale raw or, if you prefer cooked, blanch or steam kale to minimize antioxidant loss.
7. Eggplant: Cooked and grilled.
Grill eggplant to make it a lot richer in antioxidants compared to raw or boiled (and it tastes a lot better too). Don't forget to salt your eggplant slices before cooking to get rid of excess moisture and bitterness.
8. Red Peppers: Raw and cooked (stir-fry, roasted).
Red peppers are a great source of vitamin C, carotenoids, polyphenols, and other phytochemicals. Raw red peppers provide more vitamin C because vitamin C breaks down with heat. But other antioxidants like carotenoids and ferulic acid go up when red peppers are cooked.
Stir-fry or roast red peppers. Do not boil red peppers—boiling red peppers loses the most nutrients and antioxidants. Stir-frying and roasting actually preserves red pepper antioxidants, more than steaming.
9. Garlic and onions: Raw and cooked.
Garlic and onions have been linked with foods that help fight high blood pressure. Red onions have the highest amount of quercetin, a type of flavonoid family antioxidant thought to protect against certain forms of cancer, heart disease, and aging.
Garlic and onions are pretty hardy when cooked. You can blanch, fry, and even microwave them without changing their antioxidant levels by much, so prepare them however you like.
10. Artichokes: Cooked.
Cook your artichokes in order to boost their antioxidants. Steam artichokes to boost antioxidants levels by 15-fold and boil them to boost them by 8-fold. Microwaving them also increases an artichoke's antioxidants. But don't fry them-- that plummets flavonoids, a type of antioxidant.
11. Blueberries: Raw and cooked.
Blueberries are one of the fruits with the highest levels of antioxidants, and you can eat them raw or cooked to get the most antioxidants. One study found that some type of antioxidants levels went up with cooking blueberries, while others went down.
Here are some final general tips:
- Avoid deep-frying. Bad news for vegetable tempura fans: Deep-frying vegetables creates free radicals from the hot oil. Not only are free radicals damaging for the body, but the vegetables lose much of their antioxidants in the process.
- Fresh is generally better than frozen. Vegetables like spinach and cauliflower can lose B vitamins in the process of being frozen.
- At the end of the day, prepare your fruits and vegetables so that you’ll be more likely to eat them. As long as you stay away from the deep fryer, fresh fruits and vegetables will generally give you a lot more nutrients and antioxidants than processed foods.
- Try some of my favorite recipes:
Copyright © 2015 Marlynn Wei, MD, PLLC
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