High omega-3 diet of Japanese linked with significantly lower heart disease risk compared to Americans
The number of deaths from coronary heart disease among Japanese men is less than half that of American men. Whether this effect is due to genetic, dietary or other factors has not been confirmed. In the first international study of its kind, published in the August 5, 2008, issue of Journal of the American College of Cardiology, University of Pittsburgh Graduate School of Public Health assistant professor of epidemiology Akira Sekikawa, MD, PhD, and colleagues evaluated data from 868 men aged 40 to 49 enrolled in the ERA JUMP (Electron-Beam Tomography, Risk Factor Assessment Among Japanese and U.S. Men in the Post-World War II Birth Cohort) Study. Two hundred eight-one of the current study’s subjects were from Japan; 306 were Caucasian men from Pennsylvania; and 281 were Japanese-American men living in Hawaii. Blood tests measured total fatty acids and the omega-3 fatty acids eicosapentaenoic, docosahexaenoic and docosapentaenoic acids which are commonly obtained by consuming fish. Ultrasound examination assessed carotid artery intima-medial thickness (IMT), which is used to evaluate atherosclerosis. Coronary artery calcification (CAC) in the heart’s arteries, which also identifies heart disease, was assessed via electron-beam CT scanner.
Dr Sekikawa’s team found that although total fatty acid levels were similar among all subjects, the percentage of fish-based omega-3 fatty acids was twice as high among Japanese men compared with Americans of both European and Japanese descent. Japanese men had significantly less atherosclerosis, as indicated by lower average intima-media thickness and coronary artery calcification. Among Japanese men, intima-media thickness values declined with rising omega-3 fatty acid levels, a phenomenon that was not observed in either American group.
“The death rate from coronary heart disease in Japan has always been puzzlingly low,” Dr Sekikawa observed. “Our study suggests that the very low rates of coronary heart disease among Japanese living in Japan may be due to their lifelong high consumption of fish. Our study clearly demonstrated that whites and Japanese-Americans have similar levels of atherosclerosis, which are much higher than in the Japanese in Japan. This indicates that much lower death rates from coronary heart disease in the Japanese in Japan is very unlikely due to genetic factors.”
“Our study suggests that very high levels of omega-3 fatty acids have strong properties that may help prevent the buildup of cholesterol in the arteries,” Dr Sekikawa stated. “Increasing fish intake to two times a week for healthy people is currently recommended in the U.S. Our study shows much higher intake of fish observed in the Japanese [approximately 3 ounces daily] may have strong anti-atherogenic effect.”
“While we don’t recommend Americans change their diets to eat fish at these quantities because of concerns about mercury levels in some fish, increasing intake of omega-3 fatty acids in the U.S. could have a very substantial impact on heart disease,” he added.
Evidence continues to mount for omega-3s
Jun. 18–It’s hard to miss all the buzz about omega-3 fatty acids. In the grocery store the other day, I noticed that omega-3 fatty acids have been added to some brands of orange juice. Consumers now also have the choice of buying eggs and peanut butter fortified with omega-3 fatty acids.
In general, fats are described based on the predominant fatty acid present. Fatty acids are of two basic types: saturated (such as in butter) or unsaturated (such as in liquid vegetable oils). Unsaturated fatty acids, in turn, are classified as monounsaturated or polyunsaturated. Omega-3s are a type of polyunsaturated fatty acid.
The most common omega-3 fatty acids are eicosapentaenoic (EPA), docosahexaenoic (DHA) and alpha-linolenic (ALA) acids. At this time, the national dietary standards known as the Dietary Reference Intakes do not include recommended intakes for all omega-3 fatty acids. But an adequate intake has been set for ALA at 1.6 and 1.1 grams per day for men and women, respectively.
ALA is found in plant oils, including flax, canola and soybean. DHA and EPA are found in the tissues of cold-water fish such as salmon, mackerel, tuna, herring, sardines and even oysters. Cod liver also is a rich source of these omega-3s. My mother may have been right in forcing us to choke down that spoonful of cod liver oil each day.
Strong evidence exists that consumption of fish oil reduces serum lipid levels and reduces inflammation, which are both associated with cardiovascular disease risk.
In fact, many health problems are linked to chronic inflammation: cardiovascular disease, asthma, at least some types of cancer, type 2 diabetes and obesity. The anti-inflammatory effects of omega-3s are mediated by changes in the production of bioactive substances called cytokines by our white blood cells.
Evidence also suggests that consuming omega-3s may improve the body’s sensitivity to its own insulin, thus helping to maintain a healthy body weight and reducing risk for type 2 diabetes. Recent studies conducted by French researchers found that consuming 1.8 grams of EPA/DHA per day resulted in a significant loss of body fat after just two months.
While DRIs have not been established for all of the omega-3s, several expert groups have recommended increases in the amounts and types of omega-3s in the diet. Recommendations have varied from 0.5 to 1.6 grams per day (combined EPA/DHA), to 1 percent to 2 percent of total calories a day (for total omega-3’s). For a person consuming a 2,000-calorie-a-day diet, this would translate to 20 to 40 calories or 2 to 4 grams of omega-3s each day. This level of omega-3 intake can be achieved using fish oil supplements. Since a single 1-gram capsule of fish oil contains about 30 percent EPA/DHA, this would require consuming two to six capsules each day.
Another approach is to include plant sources of ALA in your diet. One of the richest sources of ALA is flax — grown right here in North Dakota. Flax oil is about half ALA. Other edible seed oils contain lesser amounts of ALA. For example, canola (also grown in North Dakota) oil has about 12 percent ALA, and soybean (again, produced here) oil contains about 7 percent.
ALA can be converted to EPA by our tissues, but that conversion provides only small amounts of EPA. One study indicated that one would need to consume 7 grams of ALA to get the same effect as 1 gram of EPA/DHA. This means one would have to consume 14 grams (1 tablespoon) of flax oil (50 percent ALA) to get the same effect.
Unlike fish oil, flax and flax oil can be incorporated into many foods without great effects on flavor, texture and other characteristics. For this reason, consumers are being presented choices of foods fortified with omega-3s from plant oils. This trend is bound to continue as more evidence emerges about the health benefits of ALA.
Each month, scientists at the Grand Forks Human Nutrition Research Center write a column about their work and how their work affects people’s lives on a daily basis. This month’s column is written by Wesley Canfield, research medical officer, who received his medical degree from the State University of New York Health Sciences Center at Upstate.
