SAN FRANCISCO, March 30 -- While raw food diets are trendy today, the chemistry behind simple cooking may add a nutritional boost to certain vegetables. Researchers report that the act of cooking helps to increase the availability of iron already contained in such vegetables as asparagus, broccoli, cabbage, and tomatoes, making it easier for your body to absorb. The research was presented here today at the national meeting of the world's largest scientific society, the American Chemical Society.
Vegetarian diets are naturally lower in iron, and iron deficiency anemia is "the most prevalent nutritional problem in the world today," according to the authors, from the Rutgers University Department of Food Science and the Center for Advanced Food Technology in New Jersey and the Asian Vegetable Research and Development Center, an international agricultural research center in Taiwan. They said their findings could help populations in developing countries, as well as vegetarians in developed nations, to boost their nutritional absorption of iron. They presented their research at the weeklong 219th national meeting of the American Chemical Society, which is expected to attract some 20,000 attendees.
"If you eat a vegetarian diet, there's extra iron available to you - and cooking can help you get the best out of what's available," said Rutgers researcher Tung-Ching Lee, who presented the findings. He said the approach of building on nutritional capabilities already locked in the vegetables offered a unique approach to solving dietary issues.
Cooking enhanced the bioavailability of iron in 37 of the 48 types of vegetables tested. Some 35 percent had low iron bioavailability when raw that was substantially enhanced by cooking. They included:
- amaranth leaf, with an increase from 5.1 percent to nearly 12 percent,
- broccoli flowerets, which jumped from 6 percent to more than 30 percent,
- cabbage, which increased from 6.7 percent to 26.7 percent,
- coriander leaf, which increased from 1.3 percent to just over 8 percent and
- leek flower, which increased from 5.2 percent to just over 16 percent.
Some vegetables tested had a naturally high bioavailability of iron even when raw, and for red and green peppers and tomatoes, this was enhanced further by cooking. Green peppers nearly doubled in availability of iron after cooking, moving from 16.7 percent to 32.4 percent, with red peppers' iron availability increasing less dramatically, from 23.7 percent to 29.1 percent. Cooked tomatoes' iron availability increased from 24.6 percent to 33.8 percent.
The research team also tested fruits in the same way, but found that cooking had less of an effect on iron bioavailability. An exception was peaches, which, when cooked, saw iron bioavailability jump from 0.8 percent to 13.5 percent.
While many cooking sources recommend using an uncoated cast-iron pan to boost the iron content in foods, Lee cautioned that this method only increases the iron content in the food. It is no guarantee that more iron is available to be absorbed by the body.
Cold storage after cooking diminished the bioavailability of iron in cabbage by nearly half, with the cooking benefit dropping from a 20 percent increase to just over 10 percent three days after cooking. When cooking is used to boost iron intake, the researchers recommend consuming the dish the same day if possible, to reap optimal nutrition benefits.
The scientists emphasized that the cooking methods they tested, ranging from boiling to stir-frying, make iron more available and easily absorbed by the body, rather than simply boosting its content in the food.
The research is supported by the U.S. Agency for International Development, and could help to shape nutritional recommendations in developing countries, where vegetarian diets are common. Lee noted that, in many developing countries, cooking vegetables is already a health and hygiene requirement because tainted water supplies do not allow rinsing, or eating raw plant food.