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Protein from any number of sources can be part of a healthy diet. But figuring out just how much or how little of each to include can be tricky. We've known for some time that most Americans need to cut back on their consumption of red meat because of its high saturated-fat content. But now some health experts are raising the possibility that eating too much fish--long a staple of heart-healthy diets--may expose folks to dangerous levels of mercury and other poisons. That's still being debated. A study published in August suggests that most of the mercury found in fish is of a form that is not particularly toxic to humans. So if your choice is between the third helping of swordfish that week and a Big Mac, go for the swordfish.
Overall, how much protein do you need? Given the popularity of high-protein diets, you may be surprised to learn that there hasn't been much research on the long-term health benefits and risks of eating lots of protein, though there is concern that too much protein can lead to kidney and liver problems. Scientists have calculated the minimum amount needed to keep your muscles from breaking down--just under 70 grams, or about 2 1/2 oz., a day for someone who weighs 150 lbs. (Food is so plentiful that Americans rarely develop protein deficiencies.) Whether high levels of protein are linked to an increased risk of developing cancer or heart disease remains unclear.
What is known is that too much protein of any kind can leach calcium out of your body and that eating lots of animal protein usually means you're increasing your intake of saturated fat as well. "I don't believe any nutritionist would argue that 30% protein isn't a reasonable upper limit for long-term safety," says Roberts at Tufts. But what is safe and what is ideal are two different matters. Current federal guidelines suggest that adults get 10% to 15% of their daily calories from protein.
If you're like most people, what interests you about high-protein diets is the possibility that they might make it easier to slim down. Preliminary evidence suggests this may be the case over the short run, but in many ways, that is almost beside the point. "People forget they should be eating a nutritious, healthy diet for other reasons," says Barbara Rolls, professor of nutrition at Pennsylvania State University. "They go on these kooky weight-management fad diets, and they lose all sight of bone and cardiovascular health."
So remember, a little protein goes a long way. Your muscles will not fall apart if you don't eat protein at every meal. Stick with leaner cuts of meat and give preference to beans, fish, chicken or pork over red meat.
The basic rules for eating smarter couldn't be simpler. Watch your total calorie intake. Burn off as many calories as you take in. And be choosy about the foods you eat--not just for a couple of weeks or months but for the rest of your life. "It takes work," says Dr. John Swartzberg, who chairs the editorial board of the U.C. Berkeley Wellness Letter. "We live in a fast-food world." The sooner we accept that that is not the healthiest of environments for us, the better off we'll be.
So, what's for dinner?
--Reported by David Bjerklie and Amanda Bower/New York, Laura Locke/San Francisco, Maggie Sieger/Chicago, Frank Sikora/Birmingham and Cathy Booth Thomas/Dallas