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AHA: Increased seafood intake may decrease CVD risk
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Eating one to two meals with seafood may reduce the risk for CHD, congestive HF, sudden cardiac death and ischemic stroke, according to a scientific advisory from the American Heart Association published in Circulation.
“Since the last advisory on eating fish was issued by the [AHA] in 2002, scientific studies have further established the beneficial effects of eating seafood rich in omega-3 fatty acids, especially when it replaces less healthy foods such as meats that are high in artery-clogging saturated fat,” Eric B. Rimm, ScD, FAHA, professor in the departments of epidemiology and nutrition and director of the program in cardiovascular epidemiology at Harvard T.H. Chan School of Public Health, professor of medicine at Harvard Medical School and chair of the writing committee, said in a press release.
Sources of omega-3 fatty acids
The highest levels of long-chain omega-3 polyunsaturated fatty acids are seen in cold-water oily fish such as tuna, salmon, anchovies and sardines, and the lowest levels are found in lobster, shrimp, tilapia, scallops and cod, according to the advisory.
Diets like the Dietary Approaches to Stop Hypertension (DASH) recommend consuming at least one to two servings of fish per week. These recommendations are also seen in the AHA 2006 Diet and Lifestyle Recommendations, the 2015-2020 Dietary Guidelines for Americans and the Scientific Report of the 2015 U.S. Dietary Guidelines Advisory Committee.
Seafood with long-chain omega-3 polyunsaturated fatty acids have been found to lower the likelihood of prolonged QT, lower heart rate, slow atrioventricular conduction and provide optimal values of various heart rate variability components, which all reduce the risk for developing sudden cardiac death and ventricular arrhythmias. Long-chain omega-3 polyunsaturated fatty acids also enhance arterial elasticity, reduce serum triglyceride concentrations in patients with hypertriglyceridemia and provide a cardioprotective effect on platelet-monocyte aggregation.
Seafood intake can reduce BP by its vasodilatory effects, which can potentially be achieved through fish oil supplements. Evidence is limited for dietary sources of long-chain omega-3 polyunsaturated fatty acids.
The risk for arrhythmic cardiac death is also reduced by increased seafood intake, which is due to greater myocyte electric stability, lower heart rate, reduced vulnerability to nonfatal and fatal ventricular arrhythmias and improve heart rate variability. Studies have found that the risk for sudden cardiac death is reduced by 50% in patients who ate one to two fatty fish meals per week compared with those with little to no seafood intake. The benefits of seafood intake may be dependent on its preparation, with more benefit seen in fish that is not breaded or fried. There may also be a threshold effect with seafood, as there is minimal additional benefit with increased seafood intake.
There are few studies that analyzed the effects of seafood intake on the risk for congestive HF. Some studies found no significant association between intake and the incidence of congestive HF, whereas other studies found that fried seafood was linked to an increased risk for the condition.
“If the positive association with fried seafood is causal, it suggests that the true effect size estimated for total seafood intake with congestive heart failure risk might be underestimated in studies that fail to account for preparation methods,” Rimm and colleagues wrote.
Various studies, reviews and meta-analyses have found that there is an inverse association between seafood and dietary long-chain omega-3 polyunsaturated fatty acids for the risk for CHD in healthy patients. There are limited meta-analyses on the effects of food substitution.
“An individual’s risk of CHD would be substantially lowered if he or she increased seafood consumption to two meals per week by substituting seafood for processed meat, but the estimated risk reduction may be substantially less (or not at all) if the two seafood meals per week were substituted for healthy vegetarian meals,” Rimm and colleagues wrote.
Seafood intake was also shown to reduce the risk for ischemic stroke, although there was little to no effect on hemorrhagic stroke. One meta-analysis found that patients who consumed one serving of seafood a week had a 14% reduced risk for ischemic stroke compared with those with infrequent or no seafood consumption.
Secondary CV events
Small studies have analyzed the effects of seafood intake on the risk for secondary CV events. There were inverse associations between both diet and supplement intakes of long-chain omega-3 polyunsaturated fatty acids and the risk for recurrent events, although they were not statistically significant.
Some issues may arise with increased seafood intake, according to the advisory. There have been concerns of increased omega-6 polyunsaturated fatty acid intake attenuating the benefits of long-chain omega-3 polyunsaturated fatty acids from seafood, although there are no significant data showing this interaction. Mercury is found in large predatory fish such as bigeye tuna and swordfish, and existing evidence does not support that there are significant adverse effects on CVD endpoints.
“If mercury in fish has an unfavorable effect on CVD risk, the available evidence suggests that the benefits of one to two servings a week outweigh the risks, especially if a variety of seafood are consumed,” Rimm and colleagues wrote.
An area that should be researched further is the effects of an increased intake of dietary trimethylamine N-oxide on CVD risk, according to the advisory.
“The 2015-2020 Dietary Guidelines for Americans include seafood as a component of the healthy U.S. diet, the DASH diet and the Mediterranean diet,” Rimm and colleagues wrote. “Others such as the Nordic diet, the Prudent diet and the Alternative Healthy Eating Index also have seafood recommendations ... and all have been consistently linked to lower risk of CHD. In sum, the current scientific evidence strongly supports the recommendation that seafood be an integral component of a heart-healthy dietary pattern.” – by Darlene Dobkowski
Disclosures: Rimm reports he is a consultant for C/O Health Inc., the Culinary Institute of America and IKEA. Please see the advisory for all other authors’ relevant financial disclosures.
Perspective
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Jo Ann S. Carson, PhD, RDN
The AHA has for a long time promoted regular intake of fish. This is an update, so it gives us a current reference that has looked at the most recent studies. It’s helpful to have a current statement from the AHA about seafood.
This advisory is not changing something, so it can be considered a continuation of the advice that we would have given individual patients about the value of incorporating fatty fish in their diet regularly.
It also gives people who are providing food to others something to pay attention to. In the hospital cafeteria here at UT Southwestern Medical Center, they serve fish regularly in nice, tasty ways that’s not fried.
When I think of clinical practice, I think of seeing an individual patient in the hospital or in the clinic, but this advisory also has relevance for policies across the country. The AHA’s guidelines indicate not only that you should be eating healthy, but you should be promoting a healthy food environment. It’s a good thing to encourage people to incorporate healthy fish in the menus that they serve to others.
In considering future research, it would be good to be able to sort out how much of the benefit is because people are eating fish in place of sausage, salami or other unhealthy meats and how much of the benefit is coming directly from the provision of the omega-3 that the fish or seafood is providing.
In terms of a message to the public, we see fish as a good, healthy protein source. The public these days are protein-conscious and some people are following a rather high-protein diet. I wouldn’t necessarily encourage people to follow a high-protein diet, but non-fried fish a good example of a healthy protein source that’s a good thing to incorporate into your diet.
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