Sure, you're basing your diet around plenty of healthy, minimally-processed foods – which of course includes several servings of vegetables. But are you getting the most out of your veggies when it comes to nutrient content?
If you're boiling your veggies into oblivion, you may not be. Lengthy cooking times and prolonged exposure to water both degrade the nutrients in your vegetables, making the cooked versions slightly less nutrient-dense than the raw ones.
In general, simply eating any healthily-prepared veggies means you're doing well in following a healthy diet. But if you want to maximize the nutrition you get from every bite, being mindful of how cooking affects nutrient density can help.
Heat and Water: The Enemies of Water-Soluble Vitamins
Why is boiling so bad? Because it involves high heat and direct exposure to water – a one-two punch for nutrient degradation. Heat can make some compounds – including certain vitamins, like vitamin C – less stable, so they start to break down before the food reaches your mouth. And water-soluble nutrients, like the B vitamins as well as vitamin C, can seep into the cooking water, and then be literally thrown down the drain.
Oxidation Degrades Nutrients, Too
Exposure to air and cooking oil can degrade your veggies' nutritional value, too. Some of vegetables' health benefits come from their antioxidant content – but some of those antioxidants can become oxidized during cooking, rendering them ineffective. Cooking oil continuously oxidizes as it heats up, neutralizing the antioxidants in the veggies, and air can have a similar – though slower – effect as well.
But There's an Upside
In some cases, cooking will actually increase the nutritional value of your veggies. Carotenoids – a family of antioxidants that give certain vegetables a red, yellow, orange or pink hue – tend to become more bioavailable after cooking. Carrots, for example, contain much more useable beta-carotene – an orange carotenoid your body converts into vitamin A – after cooking. And cooked tomatoes supply more lycopene, a powerful red-hued antioxidant, than raw ones.
The Bottom Line: Include Variety
If you want to get the most nutrition from each serving of veggies, tailor your cooking style depending on the food's nutrient content. Make a delicious side dish by roasting carrots until tender, or grill tomatoes for a more lycopene-rich salad.
For other veggies, stick to methods that cook your food quickly and with minimal exposure to water. Steam that side of broccoli, or sauté your spinach in a splash of low-sodium stock instead of cooking oil.
Alternatively, just cook your veggies however you like them best. What's most important is eating plenty of veggies overall – not stressing over the minutiae of cooking methods.