By Maryann Tomovich Jacobsen, MS, RD
“The nutrients in fruits and vegetables are severely depleted with boiling,” my brother-in-law recently said during a family get together. I know that there are some nutrient losses with cooking and processing, but the way he sounded (so certain) made me go “hmmm.”
So I looked into it and found, like all things nutrition, it’s not that black and white.
The benefits of fresh
When it comes to produce, the best case scenario for maximizing vitamin and mineral content is to get local produce and eat it in its natural state as soon as you can. According to a 2007 review in the Journal of the Science of Food and Agriculture, storage time and cooking of fresh produce can decrease its original nutrient content by almost half.
For example, water soluble vitamin C is sensitive to heat, light, and oxygen. When fresh fruits and vegetables are stored correctly and eaten in a short period they have more vitamin C. Yet research indicates that after seven days of storage, green beans can lose as much as 77% of their vitamin C. Obviously, items flown in from faraway places are subjected to more of the elements, contributing to nutrient loss.
Does cooking destroy Nutrition?
When produce is heated it will lose some nutrition, especially water-soluble nutrients like vitamin C and B vitamins. According to a 2007 study in the Journal of Food Quality, vegetables that were microwave-steamed and stir-fried with oil had better vitamin C retention than those that were boiled. Pressure cooking vegetables has also been found to result in good vitamin C retention.
But don’t stop the boiling yet. Another 2008 study in Journal of Agriculture and Chemistry revealed that while vitamin C levels decrease with boiling, certain antioxidants increase, causing vegetables to release beneficial antioxidants — and make new ones. For carrots, total carotenes (including lutein) increased in the boiled sample vs. the raw and steamed versions. In broccoli, boiling and steaming caused total carotenes to increase compared to fresh. Frying vegetables had a negative effect on antioxidants and vitamin C.
How do frozen and canned stack up?
Frozen fruits and vegetables, which are picked at peak season, get blanched before freezing, which causes some loss of vitamin C, but storage time causes further losses (due to oxygenation). The heating process that takes place before canning causes anywhere from 10 to 90% of vitamin C loss but other nutrient levels change little during storage because there is no oxygen.
Water-soluble B vitamins — thiamin, B6, and riboflavin — are also sensitive to heat and light so there is loss in canned products and during the blanching step (20-60% loss) prior to freezing. Mineral, fiber, protein, carbohydrates, and fatty acid composition in frozen and canned products are comparable to fresh.
Yet there are instances where canned items have additional benefits. For example, canned tomato products have higher levels of beta-carotene and lycopene than fresh tomatoes. In fact, a 2008 study in The British Journal of Nutrition discovered that 80 percent of raw food eaters fell short on lycopene, which is higher in cooked tomatoes.
The bottom line
Nutrient loss in fruits and vegetables is not as simple as “eat raw and don’t boil.” Instead, incorporate a variety of fruits and vegetables including raw, cooked, frozen and canned. Try to eat your fresh items in a timely manner and don’t let frozen produce sit in the freezer too long.
But most importantly, prepare fruits and vegetables in ways that your taste buds find pleasing because you’re more likely to eat them that way. And in the end, that’s what really counts.