People no longer need avoid shrimp for its high cholesterol. Steamed shrimp, naturally low in fat, can be included in heart-healthy diets for people without lipid problems, report scientists from The Rockefeller University and the Harvard School of Public Health in the November American Journal of Clinical Nutrition.
"Most high-cholesterol foods are also high in saturated fats, which people should restrict in their diets. But we found that steamed shrimp, high in cholesterol but very low in fat, do not adversely affect the lipoprotein profile in people with normal cholesterol levels. In fact, if shrimp are substituted for beef or other high fat foods, we predict even more favorable effects," says first author Elizabeth De Oliveira e Silva, M.D., research associate in The Rockefeller University Laboratory of Biochemical Genetics and Metabolism. A meal containing 150 grams, about 5 ounces, of steamed shrimp provides only 1.7 grams of fat, including 0.36 grams saturated fat, and 150 calories, compared to 150 grams of beef, which contains 14 grams of fat, including 4.7 grams of saturated fat, and 390 calories.
Shrimp is second only to tuna fish as the most frequently eaten seafood in the American diet, according to the National Fisheries Institute. Yet despite this popularity, shrimp has not been previously tested for its effect on lipoproteins in such a meticulous manner, according to De Oliveira e Silva.
Lipoproteins are large molecules that transport fat and cholesterol in the body. Lipoproteins contain combinations of cholesterol, small proteins and triglycerides, which include saturated, monounsaturated and polyunsaturated fats. High levels of low density (LDL) and very low density (VLDL) lipoproteins contribute to heart attacks by causing atherosclerosis, blockages of the heart's arteries that affect millions of Americans annually. In contrast, increases in high density (HDL) lipoproteins reduce the risk for heart disease.
"We were surprised, but pleased, to find that a low-fat diet with shrimp did not impair lipoprotein profiles," says senior author Jan L. Breslow, M.D., Frederick Henry Leonhardt Professor and head of the Laboratory of Biochemical Genetics and Metabolism at Rockefeller. Breslow, senior physician at The Rockefeller University Hospital, also is president of the American Heart Association (AHA).
The scientists suggest the findings stem from, individually or in combination, an inefficiency in absorbing shrimp cholesterol or from minor differences in the amount and kind of beneficial polyunsaturated fats, called n-3 fatty acids, in the three diets tested. "The slightly higher n-3 fatty acid content in the shrimp diet might account for the findings of lower triglycerides and higher HDL with shrimp consumption, both of which could be beneficial," explains De Oliveira e Silva.
In the study, the scientists tested the effects of including shrimp in a low-fat diet among 18 healthy adults who stayed at The Rockefeller University Hospital Clinical Research Center. During the nine-week study, the researchers randomly assigned each participant to a sequence in which they consumed three diets in rotation for a total of three weeks each: a baseline low-fat diet, the baseline plus shrimp diet and the baseline plus egg diet. The diets were carefully prepared and weighed to meet each person's caloric needs to maintain weight and provide the same nutritional composition of 15 percent protein, 55 percent carbohydrate and 30 percent fat, including the same quantity of saturated, monounsaturated and polyunsaturated fats.
The diets only differed in the amount of cholesterol. The baseline diet contained only 107 milligrams per day of dietary cholesterol. The shrimp diet included about 300 grams, or 10 ounces, of shrimp a day, which provided 590 milligrams/day of cholesterol, while the egg diet with two large hard-boiled, grade A eggs daily contained 580 milligrams/day. The AHA recommends that people have no more than 300 milligrams of cholesterol each day.
The researchers included a comparison diet using eggs because they are high in cholesterol. Eggs have, per yolk, 5.1 grams total fat, 1.6 grams of saturated fat and 213 milligrams of cholesterol. Eggs can increase the level of LDL level, which raises the risk of heart disease. The AHA recommends that people restrict eggs to three or four per week.
"Eating shrimp produced lower ratios of total to HDL cholesterol, and of LDL to HDL cholesterol compared to the egg diet, as well as significantly lower triglyceride levels than either the baseline or egg diets. Furthermore, the shrimp diet did not increase levels of heart damaging VLDL cholesterol," says Breslow.
When compared with the baseline diet, both the shrimp and egg diets produced similar increases in the LDL concentrations, 7.1 and 10.2 percent respectively, however the shrimp diet tended to increase HDL more than the egg diet, 12.1 and 7.6 percent respectively.
Breslow and De Oliveira e Silva's co-authors include Cynthia E. Seidman, M.S., R.D., Lisa Cooper Hudgins, M.D., and Jason J. Tian, Ph.D., from Rockefeller and Frank M. Sacks, M.D., from Harvard. The National Heart, Lung and Blood Institute and the National Center for Research Resources, both of the federal government's National Institutes of Health (NIH), supported the study.
Established in 1910, the Rockefeller University Hospital is the oldest in the United States devoted solely to experimental medicine. The hospital links laboratory investigations with bedside observations to provide a scientific basis for disease detection, prevention and treatment. This special hospital environment served as the model for the Warren G. Magnuson Clinical Center, opened at the NIH in 1953, and similar facilities supported by federal funding at more than 75 medical schools in the United States.
Rockefeller began in 1901 as the Rockefeller Institute for Medical Research, the first U.S. biomedical research center. Rockefeller faculty members have made significant scientific achievements, including the discovery that DNA is the carrier of genetic information and the launching of the scientific field of modern cell biology. The university has ties to 19 Nobel laureates, including the president, Torsten N. Wiesel, M.D., who received the prize in 1981. Recently, the university created four centers to foster collaborations among scientists to pursue investigations of Alzheimer's Disease, human genetics, neurosciences and the links between physics and biology.
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