In my previous post, I discussed why the mercury content of fish is not worthy of concern for most fish species (see this post). My point isn’t just that we don’t need to worry about eating too much fish; we should really be eating way more of it!
It completely frustrates me that it is generally recommended for pregnant women to limit seafood consumption to two 6oz servings per week in order to avoid excess mercury exposure. Many women take this a step further and avoid all seafood while pregnant. Some even avoid seafood while lactating. Not only is the mercury exposure from seafood a complete non-issue (with the exceptions of the few fish that are higher in mercury than selenium), but by limiting seafood during pregnancy, women are missing out on the best food source of DHA, an extremely essential nutrient for their health and the health of their growing baby. In fact, a maternal diet rich in DHA has been shown to improve a baby’s IQ by 10 points. The recommendation should probably be for a minimum of three 6oz servings of oily cold-water fish per week for these women, if not a diet that is heavily based on fish as a protein source (although, there still is a legitimate rationale for avoiding sushi). I personally wonder how different my two pregnancies would have been if I had known this back then.
Fish and other seafood should be a major part of everyone’s diet. What are the health benefits of fish and other seafood?
Fish and shellfish are rish in long chain omega-3 fatty acids DHA and EPA. These are the anti-inflammatory omega-3 fats that are readily used by our body. The shorter chain omega-3 ALA, which is in flax, chia and walnuts, is actually not easily used by our body because it must first be converted into DHA or EPA, which is a very inefficient process. A 3.5oz serving of wild-caught salmon (fresh or canned; any species), sardines, albacore tuna, trout or mackerel has over 500mg of DHA + EPA. Fish which have moderate amounts of DHA+EPA (150mg-500mg per 3.5oz serving) include haddock, cod, hake, halibut, shrimp, sole, flounder, perch, bass, oysters, crab and farmed salmon).1 Why not just get your DHA and EPA from fish oil supplements? These polyunsaturated fats are very easily oxidized in response to heat or light and are not very shelf stable, especially once isolated. Consuming oxidized omega-3 fats is not helpful to your health (contributes to inflammation as opposed to reducing it). Eating fresh, frozen or canned whole fish protects the omega-3 fats from oxidation plus provides all the necessary cofactors for optimal absorption and use by the body.
The protein in fish and shellfish is very easy to digest and research shows that the amino acids in fish are more bioavailable (your body can absorb and use them more readily) than beef, pork or chicken 2,3. Fish and shellfish also have a balanced quantity of all of the essential amino acids, giving them very high Amino Acid Scores (see http://nutritiondata.self.com).
Fish is also rich in two very important minerals which can be challenging to get in sufficient quantities from other foods: iodine and selenium. Iodine (which is also rich in algae and seaweed) is vital for normal thyroid function but is also extremely important for proper immune system function, wound healing, and fertility. Table salt is enriched with iodine due to rampant dietary iodine deficiency (goiters were very common before the advent iodized salt). Since Paleo diets tend to be lower in salt (and many people switch to sea salt, which is not iodized), it is very important to include food sources of this essential mineral. Selenium is required for a class of enzymes called selenoenzymes which are part of the body’s natural protection against oxidants. Selenoenzymes are particularly important for protecting the brain against oxidative damage, but selenium deficiencies are also linked to thyroid disease, cardiovascular disease and cancer.
Fish is also a food source of Vitamin D (which can also be found in organ meats). Vitamin D is a steroid hormone that controls expression of more than 200 genes and the proteins those genes regulate. Vitamin D is essential for mineral metabolism (it regulates absorption and transport of calcium, phosphorous and magnesium) and for bone mineralization and growth. Vitamin D is also crucial for regulating several key components of your immune system, including formation of important anti-oxidants. Very importantly, Vitamin D has recently been shown to decrease inflammation and may be critical in controlling auto-immune and inflammatory diseases. Vitamin D is also involved in the biosynthesis of neurotrophic factors, regulating release of such important hormones as serotonin (required not only for mental health but also for healthy digestion!). Vitamin D helps control cell growth, so it is essential for healing. Vitamin D also activates areas of the brain responsible for biorhythms. Scientists continue to discover new ways in which Vitamin D is essential for human health; for example, Vitamin D may prevent cancer. As we spend less and less time outdoors (our bodies synthesize Vitamin D in response to sun exposure), dietary vitamin D becomes more and more important.
Which fish are best to include in your diet? Oily cold water, wild-caught fish will have the highest omega-3 and Vitamin D content. However, even fresh water white fish are an excellent source of protein. The only fish that are worth limiting in your diet are farmed tilapia and farmed catfish as these fish tend to have higher omega-6 content 1 (they still have that great easily digested protein though!). Yes, fish can be expensive. Canned fish (especially sardines and salmon) are great inexpensive options. Pickled herring and smoked kipper are often less expensive as well. I can usually find frozen wild-caught pink salmon fillets on sale for $4 per pound at my local grocery store (which means it’s cheaper than ground beef!). The take home message here is that fish is good for you, so eat it as often as you want.
1 Gene Smart “Guide to Omega-3 Levels of Fish”
2 Faber, TA et al. “Protein digestibility evaluations of meat and fish substrates using laboratory, avian,and ileally cannulated dog assays” J ANIM SCI 2010, 88:1421-1432.
3 Sheeshka J and Murkin E “Nutritional Aspects of Fish Compared with Other Protein Sources” Comments on Toxicology 2002. 8(4-6):375-397
4 Protein Efficiency Ratio Table 6-13