Expert Answers to Readers’ Questions
- Should I be concerned about mercury and PCBs in fish?
- Are high-protein diets bad for the heart?
- How much protein do I need each day?
Fish is a good option for a protein source since it is low in fat and high in omega-3 fatty acids. Research suggests that eating just 6 ounces per week of fatty fish, such as salmon or sardines, may be enough to reduce the risk of dying from heart disease by 36 percent and reduce the overall risk of death by 17 percent. This makes fish perhaps one of the healthiest foods that you can eat.
Although there has been some recent concern about contaminants in fish such as mercury and PCBs, the evidence suggests that the proven health benefit of fish consumption is much greater than the potential for harm among adults who consume fish one to two times per week. Except perhaps for a few fish species that are higher in mercury, the scales also tip in favor of fish consumption for women who are pregnant. While high intake of mercury appears to hamper a baby’s brain development, low intake of omega-3 fats from fish is at least as dangerous, since omega-3 fats are crucial for brain development.
So, the healthiest approach for women who are or may become pregnant, for nursing mothers, and for young children is to eat two servings per week of fish or other seafood, including up to one serving per week of white (albacore) canned tuna, and to avoid the four fish species that are highest in mercury: shark, swordfish, tilefish, and king mackerel. In addition, check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don’t consume any other fish during that week.
It is important that women recognize that the list of fish and seafood that they and their children should eat is far larger than the few specific species to be avoided. Also, it’s important to realize that the restrictions on shark, swordfish, tilefish, and king mackerel apply only to pregnant women, nursing women, and children—not to the rest of the population, for whom the evidence supports simply choosing a variety of fish and seafood.
To learn more, read Fish: Friend or Foe?
One concern about the high-protein diet craze has been that eating diets high in protein and fat, and low in carbohydrate, would harm the heart. Recent research provides reassurance that eating a lot of protein doesn’t harm the heart. In fact, it is possible that eating more protein, especially vegetable protein, while cutting back on easily digested carbohydrates may benefit the heart. A 20-year prospective study of 82,802 women found that those who ate low-carbohydrate diets that were high in vegetable sources of fat or protein had a 30 percent lower risk of heart disease, compared with women who ate high-carbohydrate, low-fat diets. But women who ate low-carbohydrate diets that were high in animal fats or proteins did not have a reduced risk of heart disease.
So if you are going on a lower carbohydrate diet, do your heart a favor by choosing vegetable fats and protein sources. And to reduce the risk of colon cancer, limit red meat to no more than 18 ounces per week, and avoid processed meats (such as bacon, hot dogs, and ham).
There is no one-size-fits-all answer to that question, and research on the topic is still emerging. The Institute of Medicine recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day—that’s about 58 grams for a 160 pound adult. In the U.S., adults get an average of 15 percent of their calories from protein; for a person who requires a 2,000-calorie-per-day-diet, that’s about 75 grams of protein. In healthy people, increasing protein intake to 20 to 25 percent of calories can reduce the risk of heart disease, if the extra protein replaces refined carbohydrates, such as white bread, white rice, or sugary drinks. Higher protein diets can also be beneficial for weight loss, in conjunction with a reduced calorie diet, although long-term evidence of their effectiveness is wanting.
For people in good health, consuming 20 to 25 percent of calories from protein won’t harm the kidneys. For people with diabetes or early-stage kidney disease, however, the American Diabetes Association recommends limiting protein intake to 0.8 to 1.0 gram of protein per kilogram of body weight (roughly 10 percent of energy intake), since this may help improve kidney function; in later stage kidney disease, sticking to the 0.8 grams per kilogram minimum is advisable. Consult a doctor or a registered dietitian for individualized protein recommendations.
The aim of the Harvard School of Public Health Nutrition Source is to provide timely information on diet and nutrition for clinicians, allied health professionals, and the public. The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site. The information does not mention brand names, nor does it endorse any particular products.