Nutrition Hotline
By Reed Mangels, PhD, RD
QUESTION: “Are the omega-3 benefits from flaxseeds or their oil destroyed by heat from baking or cooking?”
P.L., via e-mail
ANSWER: According to the Flax Council of Canada (
Flax oil generally should not be used for cooking, as it is not stable at high temperatures. It is often added to foods after they have been cooked. For example, you can toss it with steamed vegetables or cooked pasta. Some research suggests that flaxseed oil can be used in baking without loss of omega-3 fatty acids.
QUESTION: “I teach vegan cooking classes for cancer patients and find that, when they are undergoing treatment, they turn to the convenience and extra calories of dairy-based drinks like Ensure. Are there easy, non-dairy alternatives for cancer patients?”
J.M., via e-mail
ANSWER: There are a few commercial soy-based smoothies and shakes that require no preparation and that can add protein and calories. Examples of these products are Whole Soy Smoothies, SilkLive Smoothies, and Westsoy Shakes. These all provide between 170 and 230 calories per serving. Depending on the product, a serving is either 8 or 10 ounces. For comparison, an 8-ounce can of Ensure provides 250 calories. The soy products provide either 7 or 9 grams of protein per serving compared to Ensure's 9 grams of protein per serving.
Another alternative is to make a super-smoothie by blending one of these products with some frozen fruit and either soy yogurt, soy frozen dessert, or silken tofu. A little flaxseed oil can also be added to increase calories and provide some omega-3 fatty acids.
Product Websites:
Whole Soy Smoothies
SilkLive Smoothies
Westsoy Shakes
QUESTION: “What effect, if any, does being a vegetarian have on female puberty and on menstruation in general? Is there any effect if someone starts being vegetarian mid-puberty?”
L.M., MN
ANSWER: Overall nutritional status is an important factor in determining at what age puberty occurs. On average, puberty occurs earlier in well-nourished girls as opposed to poorly nourished girls and is earlier in those who are heavier for their height.
Some studies have suggested that vegetarian girls have a slightly later age at menarche, possibly because vegetarian girls tend to be leaner than non-vegetarians. Other studies have found no difference in age at menarche between vegetarian and non-vegetarian girls who had similar calorie intakes.
The question of whether becoming a vegetarian during puberty has an effect on puberty has not been studied directly, although we do know that earlier menarche is associated with higher intakes of animal protein earlier in life (before age 9). It is possible that earlier diet plays a role in age of menarche. Certainly, the nutritional quality of a vegetarian diet could have an impact on growth and development. If the vegetarian diet is nutritionally adequate, I would expect that it would have little effect on pubertal development. If it is markedly lacking in calories or nutrients, poor nutrition could delay puberty.
Vegetarian diets have been associated with menstrual disturbances (irregular cycles, periods of amenorrhea) in some studies, although these studies have been criticized because they may have included women with eating disorders who would be more likely to have altered cycles. Other studies have not found differences between vegetarian and non-vegetarian women in terms of menstrual cycles if women with eating disorders were not included in the study. Women who become vegetarian for reasons related to body weight issues appear to be at increased risk for menstrual disturbances.
REFERENCES
Barr SI. 1999. Vegetarianism and menstrual cycle disturbances: is there an association? Am J Clin Nutr 70 (suppl):549S-54S.
Barr SI. “Women's reproductive function.” Vegetarian Nutrition. Sabate J, ed. Boca Raton: CRC Press, 2001. 221-49.
