One of the tenets of the 2015-2020 Dietary Guidelines for Americans is that a healthy eating pattern includes a variety of vegetables whether dark green, red, orange or starchy. Institute of Food Technologists (IFT) member Guy Crosby, PhD, CFS, adjunct associate professor at the Harvard School of Public Health has some tips for consumers on the best way to cook veggies while preserving their nutrients.
Q: Why do vegetables soften when cooked?
A: Vegetable cells are held together by a polysaccharide known as pectin. Pectin breaks down with heat so when vegetables are cooked, the pectin starts to break down and that releases the bond between the cells. That's what causes vegetables to soften. Once that happens vitamins and minerals begin to migrate out of the cells and can be lost in the cooking water.
Q: If cooking breaks down nutrients, does the cooking method matter?
A: Yes, the method of cooking vegetables makes a big difference whether you boil, steam, microwave or fry. Factors such as cooking time and temperature, along with the type of vegetable being cooked impact how many of the nutrients are conserved.
Q: Which method is best?
A: Frying is the worst in terms of loss of nutrients due to the high heat. Boiling would be next in that you might lose between 40 to 50 percent of nutrients, sometimes less, depending on the type of vitamin or mineral. Steaming can be a better way of avoiding lost nutrients and is more or less comparable to microwaving as long as you don't microwave food too long.
Q: Does cooking ever boost nutrient content?
A: In certain cases cooking does actually enhance nutrient quality. Tomatoes are a classic example. During cooking the red pigments called lycopene in tomatoes are strengthened. Lycopene is an antioxidant shown to have several health benefits and may even reduce the risk of certain types of cancers. When you eat a tomato raw, you absorb a certain amount of that lycopene in your blood stream; but when you cook the tomato, the amount of lycopene that gets absorbed is about four times higher.
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Source: Guy Crosby, PhD, CFS, adjunct associate professor at the Harvard School of Public Health
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