Nutrition Hotline
By Suzanne Havala, MS, RD
QUESTION: A vegetarian friend told me that girls raised as strict vegetarians menstruate at a later age than girls who eat meat. Is this true?
Via e-mail
ANSWER: Possibly. A limited amount of research has shown that some girls eating a plant-based diet reach menarche — have their first periods — later than omnivorous girls. Research on Japanese women has led some researchers to conclude that later menarche and earlier menopause in Japanese women eating a traditional, plant-based diet may be associated with lower rates of breast cancer in Japanese women as compared with American women. It's possible that lower rates of breast cancer are due in some part to these women being exposed to high levels of circulating estrogens for a shorter period of their lives. It's difficult to generalize research findings from one culture to populations in other cultures, however. There is relatively little evidence, for example, that Western vegetarians have lower rates of breast cancer as compared with Western non-vegetarians.
For more information, see:
Pike MC, Spicer DV, Dahmoush L, Press MF. 1993. Estrogens, progesterones, normal breast cell proliferation, and breast cancer risk. Epidemiol Review 15:17-35.
De Waard F, Trichopoulos D. 1998. A unifying concept of the etiology of breast cancer. Int J Cancer 41:666-669.
Sanchez A, Kissinger DG, Phillips RL. 1981. A hypothesis on the etiological role of diet on age of menarche. Med Hypotheses 7:1339-1345.
Kissinger DG, Sanchez A. 1987. The association of dietary factors with the age of menarche. Nutr Res 7:471-479.
QUESTION: I'm confused. Nutrition tables always list a cup of collards as being an excellent source of calcium with about 30 percent of the RDA. However, the percentage listed on packages of frozen collards or even the cellophane bags of fresh collards is only 2 - 4 percent. Why the discrepancy between the two?
B.M. Via e-mail
ANSWER: According to Bowes and Church's Food Values of Portions Commonly Used, 17th Edition, (Lippincott Williams & Wilkins Publishers, 1997), one cup of chopped, boiled collards contains 29 milligrams of calcium. That's equal to only about two to four percent of the Recommended Dietary Allowance (RDA), depending upon age and sex. It's also equal to 3 percent of the Daily Value (DV) — the standard reference now used on food labels — of 1,000 milligrams of calcium. A half cup of frozen, chopped, boiled collards is also listed by Bowes and Church as containing 179 milligrams of calcium, or 358 milligrams in a cup (there's your 30 percent of the RDA).
There are several possible explanations for the discrepancy you've cited. The difference may be due to whether the analysis was done before or after cooking. Since greens become more compact when they cook, a half cup of cooked greens contains more nutrients than the same amount of raw greens. Content of natural foods like collard greens will vary considerably depending on soil conditions, use of fertilizers, water supply, etc. Generally, dark green, leafy vegetables like collards are considered to be a good source of available calcium. However, because of the possible variability in their calcium contents, we recommend use of a variety of calcium-containing foods to ensure that calcium needs are met.
