Nutrition Hotline: This issue's Nutrition Hotline reviews whether there are nutritional differences between canned and cooked beans and addresses the myths surrounding soy

Vegetarian Journal, May-June, 2003 by Reed Mangels

QUESTION: "I use canned beans most of the time because I just don't have time to cook beans and I never seem to remember to soak them ahead of time. What is the difference between canned and cooked beans, nutritionally speaking?"

ANSWER: There's not a big difference between canned and cooked beans. The effects of heating and cooking on nutrients would be similar whether the beans are cooked or canned. Folate appears to be lower in canned beans compared to cooked beans, although a cup of canned beans still provides close to 1/3 the folate RDA for adults. Certainly, sodium will be higher in canned beans compared to beans cooked without adding salt. You can reduce the sodium in canned beans by placing them in a strainer and rinsing them well with cold water. This has been shown to reduce the sodium by as much as 40 percent. Beans are a good source of fiber, protein, iron, and zinc. Don't avoid them just because you don't have time to cook them from scratch. Canned beans are an acceptable substitute.

QUESTION: "What's going on with soy? First I heard that eating soy would help with hot flashes and would be good for my heart, now I've heard that eating soy is dangerous. What should I believe?"

ANSWER: You're right to be confused. New results of scientific studies showing the benefits of soy products appear almost daily. Possible reasons to use soy products are to fight heart disease, (1-4) promote stronger bones, (5-7) reduce risk of some kinds of cancer, (8-10) and to lose weight. (11) However, a number of websites and brochures have appeared saying that soy isn't good for people at all. Reasons for avoiding soy are often loosely based on scientific studies, but a lot of times, the results have been twisted quite a bit to make the case that soy is harmful. In reality, soy is neither the cure for all of the chronic diseases that plague an affluent society, nor is it a food that should be avoided. Soy foods can certainly add variety to a vegetarian diet, and they do offer some health benefits, but they should be a part of the diet--not the foundation for it.

Soybeans contain relatively large amounts of isoflavones. Isoflavones are a type of phytoestrogens, which are substances found in plants that have properties like the hormone estrogen. The levels of isoflavones in soy products are the most common reason for concerns about soy's effects on health. Recently a group of scientists from several different countries looked at more than 200 studies on soy safety and concluded that "the available scientific evidence supports the safety of isoflavones as typically consumed in diets based on soy, or containing soy products." (8)

If we look at the amount of soy isoflavones used in countries where soy is a regular part of the diet and where no harmful effects have been documented, perhaps this can give us some idea of a reasonable amount of soy. The average daily soy intake in Japan is about 65 grams per person, (12) and the average isoflavone intake is about 20-32 milligrams per day. (12-14) Higher intakes have been reported in China, where women's median isoflavone intake was 39 milligrams per day, and in Singapore, where the median intake was 35 milligrams per day. (15-16) To find out the isoflavone level of your diet, use the USDA's isoflavone database, (17) or look on packages of soy foods that you eat. Choosing 2-3 servings of soy per day will generally lead to an isoflavone intake similar to that seen in countries where soy is a regular part of the diet.

Here are some common areas of concern:

SOY AND INFANTS, CHILDREN, PREGNANCY

During pregnancy, isoflavones from the mother's diet appear to be passed on to the fetus. High levels of isoflavones were found in healthy Japanese infants whose mothers also had high blood levels of isoflavones, probably due to high intakes of soy. (18) These levels of isoflavone s have not been associated with any health problems in infants. One report has found that a birth defect of the penis called hypospadias occurred more frequently in infants whose mothers followed a vegetarian diet during pregnancy. (19) Although some have attributed these results to use of soy, there was no significant association between use of soymilk and other soy products and development of hypospadias. (19) Isoflavones from the mother's diet also appear in breast milk, although the daily isoflavone intake of breastfed infants remains negligible, (20) even when breast milk levels are increased as much as tenfold by the mother's use of soy foods. (21) At this point there is no scientific evidence of a need to avoid soy foods in pregnancy or during breastfeeding; 2-3 servings a day is a reasonable amount.

Ideally, all infants would be breast-fed. There are circumstances, however, where soy formula is the next-best alternative. Researchers have concluded that use of soy formula appears to have no effect on fertility, miscarriage rate, birth defects in offspring, or maturation. (22) Based on the results of this study, and calculating isoflavone intake on a body weight basis, and assuming that older children absorb and metabolize soy isoflavones similarly to infants, a daily soy intake of 2-3 servings per day appears reasonable for children.