Carol J. Lammi-Keefe
Our grandmothers were right. A common adage for many of us when we were growing up – especially if we lived in states like Louisiana with coastal waters that provided a living for its workforce – was that fish is brain food.
Today we know that our grandmothers and their old wives’ tales about fish’s healthy attributes were right on target. Fish – especially fatty fish from cold marine waters – contains fats important to the development of the brain. Recent research has demonstrated that women who consume the fats of these fish during pregnancy have babies who see better and who are better able to problem solve. In short, they are smarter!
Other benefits for fish consumption include protection against cardiac events. The American Heart Association recommends the intake of two or more servings of fatty fish per week for healthy adults. Other health benefits include:
- Prevention of preterm deliveries.
- Better mental health.
- Stronger immune systems for warding off sickness and perhaps decreased body fat.
- Protection against macular degeneration, the leading cause of blindness in the elderly.
Important to southern states like Louisiana that do not border the cold marine waters and that have fish species farmed in fresh waters is the fact that even these fish contain some of the healthy fats. Also, recent agricultural research demonstrates that the content of the healthy fats can be increased in catfish by modifying the fish meal on which they are raised. Fish fat is different from other food fat
The fats of fish that are especially healthy are the long chain omega-3 fatty acids. The two predominant omega-3 fatty acids in fish are docosahexaenoic acid (referred to as DHA) and eicosapentaenoic acid (referred to as EPA). It is important to include sources of foods containing DHA in the diet.
Evidence for the benefit of DHA in brain and eye development has come in large part from studies conducted with infants, both term and preterm. The consumption of DHA by pregnant women has shown that their infants sleep better, have better vision and are better able to figure out baby-sized problems, such as how to get at a toy slightly out of reach or hidden.
These findings point to a role of DHA during pregnancy in the in utero development and maturity of the brain and the retina of the eye. Thus, even in apparently well-nourished women, nutrition can be improved and benefit the central nervous system and retina of the eye of the child.
A longer term benefit for DHA for infants is likely in improved school performance at later ages. In fact, at least one study points to a higher IQ with supplementation of DHA during pregnancy. Additionally, two studies now provide evidence that increased DHA during pregnancy can decrease fatness in the infant. This latter finding is especially interesting at this time when obesity is increasing, and early nutrition is viewed as a critical time for intervention. Can increased fish consumption during pregnancy be one answer to Louisiana’s overweight and obesity statistics and the global obesity epidemic? How much DHA should be consumed?
Currently, we do not have official recommendations for how much DHA we should consume. However, Table 1 provides expert opinion for the intake of DHA by different segments of the population. Recent studies show that pregnant women are consuming on aver The fats of fish that are especially healthy are the long chain omega-3 fatty acids. The two predominant omega-3 fatty acids in fish are docosahexaenoic acid (referred to as DHA) and eicosapentaenoic acid (referred to as EPA). It is important to include sources of foods containing DHA in the diet. age around 54 mg DHA per day. This is much lower than the recommended 300 mg per day. What are good sources of DHA?
Good sources of DHA are cold water marine fish such as tuna, herring and salmon. Figure 1 compares the content of DHA in a normal serving of different foods. There are also a variety of manufactured or engineered foods on the market that have added DHA.
Examples of foods other than fish that may contain DHA are eggs if the hens have been fed feed that contained DHA or milk to which the DHA has been added. Consumers should read labels and look for DHA and not simply omega-3 fatty acids. Omega-3 fatty acids can include some shorter chain fatty acids that do not provide the same health benefits as DHA, so these two terms are not synonymous.
Infant formulas may or may not contain DHA. In the United States, DHA has been added to infant formulas since early 2002. Consumers must read the label to determine if products they are purchasing contain DHA. The addition of DHA to infant formulas underscores its importance to infant development. Breastmilk contains DHA, but amounts will vary depending on the mother’s diet. Breastfeeding is highly promoted and encour aged for many different reasons, but the DHA content of the breastmilk is one of the reasons to encourage this practice.
A practical guideline for increasing the consumption of DHA is to include the following in a week’s meal plan – two tuna fish sandwiches and one serving of a high DHA containing fish, such as salmon. What about warnings that pregnant women should not be consuming fish?
The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have published a joint recommendation for the consumption of fish by pregnant and breastfeeding women and young children. The concern that underlies the recommendation that these individuals limit the consumption of specific species of large fish and fish from local streams and rivers is that the fish are highly likely to be contaminated with organic chemicals (PCBs) or mercury (technically methylmercury), both of which can be harmful to the central nervous system, including the brain.
Fish that contain higher levels of mercury are those that are larger, predatory fish. This is because these fish have lived longer, and their diet includes smaller fish that also contain mercury from the water in which they reside. The fish that women of childbearing age (including pregnant women) and children should avoid consist of shark, king mackerel, swordfish, tilefish and any locally caught fish that may be contaminated. It is recommended that tuna steaks be consumed infrequently – no more than once a month. Additionally, if tuna steak is consumed, then no other fish should be consumed in that week. Canned tuna has recently been scrutinized, and the prudent recommendation is that 12 ounces per week of the chunk light tuna is a reasonable amount to eat. The chunk light is better than the albacore tuna because mercury levels tend to be lower. PCBs are another form of contaminant that can be found in fish. PCBs are believed to cause cancer, though studies are incon clusive and more research must be done to verify this belief.
Recent attention has been focused on farm-raised salmon. This is because farm-raised salmon contain higher levels of PCBs than wild salmon. Though these levels are higher (27 ppb versus 6 ppb), the levels found in these fish are still below the levels the FDA considers safe for consumption (2,000 ppb). As long as your diet does not come only from this type of fish, the benefits should outweigh the risks. The EPA recommends that consumption of farm-raised salmon should be no greater than twice per week. The FDA recommends that pregnant women:
- Consume 2-3 servings (about 12 ounces) of fish and shellfish per week.
- Vary the types of fish each week to decrease exposure to these contaminants.
- Limit the consumption of tuna steaks.
- Avoid shark, king mackerel, swordfish, tilefish and certain locally caught fish.
Canned tuna can be included in the diet and is a very good source of DHA. Canned tuna is convenient and contains lower amounts of mercury because canned tuna fish comes from a smaller species of tuna. There are differences in levels of mercury that can be found in canned fish. In studies done by the FDA, chunk light tuna has been found to have the lowest amount of mercury compared to chunk white and albacore tuna. Canned Alaskan salmon is also a great source of DHA and it contains low levels of mercury. Carol J. Lammi-Keefe, Alma Beth Clark Professor of Human Nutrition and Food, School of Human Ecology, LSU AgCenter, Baton Rouge, La.
(This article was published in the fall 2008 issue of Louisiana Agriculture.)