2004-04-15 / Medical

Nutrition

Questions & Answers
American Institute for Cancer Research
Body Mass Index Helps Determine Weight Risk
Nutrition

Questions & Answers

American Institute for Cancer Research

Body Mass Index Helps Determine Weight Risk

Q: Is BMI still considered an accurate assessment of a healthy weight?

A: Yes. But there are a few exceptions that may apply. Because muscle weighs more than fat, researchers have always warned that the Body Mass Index (BMI) overestimates body fatness in athletes with low body fat and a lot of muscle. Likewise, BMI underestimates body fat in the elderly or people who have lost a lot of muscle. Body fat can be accurately assessed by underwater weighing. Trained fitness professionals using calipers or other special equipment can also closely calculate how much body fat a person has. But in the absence of these specialized techniques, BMI has been shown to more closely represent body fatness than a simple weight measurement. Furthermore, studies show that people whose BMI classifies them as overweight experience a greater risk of cancer, high blood pressure and high cholesterol. Because most Ameri-cans lead a lifestyle that is too sedentary, a high BMI usually comes from fat, not muscle. Thus, a BMI reading is a good place to start when determining health risks due to excess weight. By taking a waistline measurement - another easy test - you can better assess health risks from body fat. For women, a waist measurement of 35 inches or more indicates high risk. For men, the significant figure is 40 inches or more.

Q: I heard that albacore tuna is high in mercury and should be avoided. Isn’t this fish good for us?

A: Albacore (white) tuna is low in saturated fat and a good source of omega-3 fat that seems to help protect against cancer and heart disease. Al-bacore tuna is not as high in mercury as shark and swordfish, but tests rank it as "medium" in content, along with haddock, halibut, grouper and several other fish. Too much mercury in food does pose health risks, especially to the nervous system of babies. There-fore, to control exposure to mercury, Food and Drug Administration (FDA) officials recommend that women who are pregnant, breastfeeding, or who might become pregnant limit albacore tuna to one serving a week. These women should restrict their total consumption of all fish and shellfish each week to 12 ounces. Other adults may prefer to do the same because a few studies suggest a link between excess mercury in the diet and heart risks. But for everyone except these women, current official recommendations consider slightly more white tuna and more total seafood each week safe. It should be noted that canned light tuna is lower in mercury than regular tuna, but it is an unreliable source of omega-3 fat. In sum, although foods clearly labeled good or bad may comfort us all, albacore tuna is an example of how a food can be healthful, even though it’s not advisable to eat it daily.

Q: If I do yoga every day, is that enough exercise to keep me healthy?

A: Yoga increases flexibility, im-proves muscle tone, relieves stress, and helps with certain types of pain management. Depending on the type of yoga, however, it may not offer enough strength-building exercise to maintain your body muscle. Further-more, fitness experts say that only power yoga, or astanga yoga, provides a good aerobic ("cardio") workout, which is important for your heart and overall well-being. If your work and daily life activities don’t increase your heart rate a little for an extended period most days, you should add in some regular walking, swimming, biking or other type of aerobic activities.

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