Nutrition, Pregnancy, and Omega-3s



FYI: My co-host Carrie Dennett has written a series of great posts on nutrition and pregnancy on You should definitely check them out. Now on to the post…

The thing about proper nutrition when you’re pregnant is the following: It’s DAMN IMPORTANT. For instance, not getting enough folate/folic acid during pregnancy can result in major neural tube defects.1–3 Think about it: You’re literally building a human from scratch. You’re going to need all the necessary components for doing that, plus some extra.

Really, the topic of nutrition and pregnancy is far too large to cover in one blog post, which is why Carrie had to break it up into several posts. So I am going to briefly touch on a few things that were discussed in the show.

Nutrition and Fertility

I mentioned Dr. Walter Willett appearing on The Diane Rehm Show some years ago to plug his book The Fertility Diet. I have not read The Fertility Diet, but Dr. Willett is chair of the department of nutrition at the Harvard School of Public Health. He is a bit of a rockstar in the field of nutrition because he has written many hard-hitting papers on the subject, and he’s a principal investigator on the Nurses’ Health Study.

I will let the science speak for itself, but one thing that struck me during the interview was that whole milk was associated with greater fertility than skim milk. So if you are a milk drinker, choose whole milk while trying to get pregnant or have a small dish of ice cream or full-fat yogurt every day.* For the other main takeaways from the fertility diet visit the HSPH website.

Prenatal Nutrition

I’m not going to go into a big long post on everything you need to know about nutrition and pregnancy. If you want something a bit more comprehensive visit Carrie’s posts linked above or check out the Mayo Clinic’s pages on what to eat and what not to eat during pregnancy. Or download this very informative review.4 Or buy a textbook on the subject.

What I would like to do is explore the topic of Omega-3 intake during pregnancy and IQ.

Omega-3s During Pregnancy and IQ

This is a very thorny issue indeed, but one that I think warrants further investigation. In that spirit I did some digging after we recorded our podcast and found the following…

A paper was published in 2005 in the American Journal of Preventive Medicine that you might call something of a meta-analysis.5 The author took all the relevant studies regarding n-3 fatty acids and cognitive development, aggregated them, and summarized their findings. This was the conclusion:

This analysis finds that an increase in maternal intake of DHA during pregnancy of 1 g/day will increase child IQ by 0.8 to 1.8 points (central estimate of 1.3 points). Because typical DHA intake associated with fish consumption is well under 1 g/day, changes in fish consumption will result in IQ effects amounting to a fraction of a point.

In other words, the evidence suggests that large amounts of DHA n-3 will have possibly the only the mildest effects on IQ. The analysis included 7 randomized controlled trials (RCTs) on formula feeding and one RCT on maternal supplementation during pregnancy. The author also points out that that there are large differences in the relevant studies so direct comparison is difficult, and that different tests were used to estimate IQ.

But what has been published since that analysis??

No Link

In 2008 a RCT published in the journal Pediatrics found nothing. From the conclusion:

Our study did not reveal any difference in overall IQ scores at 7 years of age between children whose mothers had taken n-3 very-long-chain PUFAs or n-6 long-chain PUFAs during pregnancy and lactation.

Positive Link

In 2007 an observational study was published in the Lancet where pregnant women completed a food frequency questionnaire (FFQ), and later their child was measured for pro-social behavior, fine motor skills, communication skills, and social development.6 From the paper:

[M]aternal consumption of more than 340 g seafood a week was beneficial for the child’s neurodevelopment.

American Journal of Epidemiology in 2008 published results of a cohort study that measured maternal fish intake and child cognition. Another mild association was found.

[M]aternal fish intake more than twice a week was associated with improved performance on tests of language and visual motor skills.

But what about n-3s? Some fish are sources of a ton of n-3s while others not so much. The authors accounted for n-3s. For each 100 mg of maternal daily DHA & EPA intake from fish, children had Peabody Picture Vocabulary Test (PPVT) scores that were 0.5 points higher and Wide Range Assessment of Visual Motor Abilities (WRAVMA) total scores that were 1.1 points higher – another mild endorsement of the link between n-3s and cognition. However, the authors noted that higher prenatal mercury exposure was associated with lower developmental test scores. Unfortunately, often times fish and mercury go hand in hand. Ugh… what now?

Fish and Mercury

Pregnant women are often cautioned to avoid eating too much fish because of the mercury levels. This is important, and like alluded to earlier can have impacts on the child’s cognitive development. The thing is that mercury levels can vary greatly by the type of fish, whether it was farmed or wild-caught, and where it was sourced. For more information visit the NRDC website or check out this handy chart from the University of Maine.

Nutrition and the Epigenome

We touched on nutrition, epigenetics, and the pop science book Survival of the Sickest (If you’ve read it, tell me what you think in the comments section). I’d like to discuss that area of research, but it’s so meaty7 that it requires its own post.


* However, to be clear most of the evidence presented in the book comes from the Nurses’ Health Study, which is an epidemiological study. An important fact about epidemiological studies is that they measure associations (or links) not necessarily causes. So it may be true that there is something about whole milk that produces greater fertility over skim milk, but it is also possible that more fertile women prefer whole milk over skim milk and that the milk really doesn’t affect fertility. It’s difficult to determine, and won’t be determined unless/until some sort of randomized controlled trial takes place. This is important to clarify, especially since I made the mistake of saying in the podcast that milk influences fertility. It would be more accurate to say that skim milk is associated with infertility or whole milk is linked to fertility or something like that.


  1. Honein MA, Paulozzi LJ, Mathews TJ, Erickson JD, Wong LY. Impact of folic acid fortification of the US food supply on the occurrence of neural tube defects. JAMA 2001; 285: 2981–6.
  2. Berry RJ, Li Z, Erickson JD, et al. Prevention of neural-tube defects with folic acid in China. China-U.S. Collaborative Project for Neural Tube Defect Prevention. N Engl J Med 1999; 341: 1485–90.
  3. Laurence KM, James N, Miller MH, Tennant GB, Campbell H. Double-blind randomised controlled trial of folate treatment before conception to prevent recurrence of neural-tube defects. Br Med J 1981; 282: 1509–11.
  4. Williamson CS. Nutrition in pregnancy. BNF Nutr Bull 2006; 31: 28–59.
  5. Cohen JT, Bellinger DC, Connor WE, Shaywitz BA. A quantitative analysis of prenatal intake of n-3 polyunsaturated fatty acids and cognitive development. Am J Prev Med 2005; 29: 366–74.
  6. Hibbeln JR, Davis JM, Steer C, et al. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study. Lancet 2007; 369: 578–85.
  7. Pardon the pun.

Conjugated Linoleic Acids and Grass-fed Beef

[link to mp3]

In this episode I speak to Carrie Dennett, a fellow classmate of mine1, and we discuss conjugated linoleic acids (CLAs) and grass-fed beef. Carrie writes a weekly column for The Seattle Times titled On Nutrition. Betcha can’t guess what it is about! She also blogs pretty regularly at

So what the hell are CLAs? They are a family of fatty acids that are produced in ruminants. What the hell are ruminants? Ruminants are animals with a multi-chambered stomach that have gut bacteria specializing in breaking down cellulose to glucose. Most animals (including humans) cannot do this2; the cellulose just ends up acting as dietary fiber, which has its own benefits but providing energy ain’t one of ‘em.

Ruminants include deer, sheep, goats, bison, elk… but the ruminant humans most prefer gastronomically is the good ol’ cow.3 However, the problem is that most beef produced in the US is from cattle that are fed corn4 rather than a diet of mainly grass as bovines have evolved to eat. This can be harmful to the animal. Diets of grains such as corn can directly or indirectly cause diseases in the animal and possibly whatever eats the animal. For instance, cattle fed diets of grain (i.e. corn) have more acid-resistant E.coli 0157:H7 (the bad kind) than their grass-fed counterparts.5

Cattle diets affect far more than just bacteria, of course.6 One thing Carrie and I discuss is the difference in fatty acid profile. Evidently, grass-fed beef has a much more desirable lipid profile compared to their corn-fed compatriots, not the least because of the conjugated linoleic acids they produce.7

The Science Behind CLAs

Here’s the straight dope: the actual evidence regarding CLAs are conflicting. It appears that in animal studies (usually with rodents but sometimes rabbits or hamsters) CLAs are fairly beneficial. In short they appear to decrease incidence of atherosclerosis, cancer, insulin resistance, and all kinds of good stuff! 8, 9, 10 However, nearly all of the original studies I found that suggested major significant nutritional benefits of CLAs were funded by beef or dairy producers. Here is one example:

This work was supported by a grant from the National Cattleman’s Beef Association

And another

Research grants provided by the Wisconsin Milk Marketing Board and Kraft General Foods

I’ll also kindly refer you to an earlier post where I found the exact same thing about CLAs. I’ll reproduce it here.

Funded by beef and veal producers and importers through their $1-per-head checkoff and was produced for the Cattlemen’s beef board and state beef councils by the National Cattlemen’s Beef Association

Again, as I said in the previous post, this does not mean that the findings are bogus or untrue, but I think everyone should be skeptical of studies funded by the industry that they are investigating, especially if that study happens to be in line with said industry’s financial interests (which these do). What it most likely means is that Industry X (which in this case is the beef/dairy industry) is funding research that they expect will portray their product(s) in a positive light. If favorable results come in Industry X will advertise/glorify/disseminate/publicize/trumpet/broadcast them to try and convince people that, hey, their product ain’t so bad – in fact it might be good! Unfavorable results will be ignored.

But this isn’t even the real point. The real point is what matters to humans, because, let’s face it, we don’t give a shit about how beef products affect rats or mice. All we care about is the effect on us, the Homo sapiens, so we can live longer & healthier lives.

Human Studies

Unfortunately, like Carrie mentions in the podcast, the studies in humans are inconsistent. I have a book of lipids in front of me (jealous?) that did something of a meta-analysis on 34 journal articles that were published between 2000 and 2004 examining the dietary effects of CLAs and the results are wildly inconsistent. There is a really nice multi-page table giving all the relevant details of each study: some lost body fat but not body weight, some lost weight, many had no effect on weight or anything else that was measured, some had lower cholesterol, some had increased insulin resistance, some had increased lipid peroxidation… it’s just a total mixed bag. The authors even looked at some epidemiological studies with one indicating that low intake of CLAs was associated with increased cancer risk, while another indicated that high intake was associated with increased cancer risk.11 You just cannot come to definitive conclusions with these results.

I have not been in a supplement store in years. I used to go all the time, but funnily enough the more you learn about nutritional supplements the more you begin to understand that ~95% of them are either completely bogus or just unnecessary. I don’t recall ever seeing CLAs in stores when I was young and buying ridiculously overpriced supplements, but evidently CLAs are sold as weight-loss supplements or even bulk-uppers nowadays. If you’re thinking about purchasing a $49.99 bottle of CLAs for weight-loss or some other benefit, I will leave you with a passage from one of my many nutrition textbooks.

Because some animal research reported reduced body fat following CLA supplementation, dietary supplements have been marketed to humans, including athletes, for weight loss. However, although data are limited, more recent studies reported no significant effects of CLA supplementation on fatty acid metabolism or weight loss in healthy, weight-stable women or on body mass and composition in experienced resistance-trained persons. Current research findings reveal no significant benefits of CLA supplementation to the physically active person.12

So to wrap this post up in a neat little bow: Grass-fed beef could very well be healthier than corn-fed beef, but the jury is still out. It is certainly better for the cow, though.

1. Listening back to the episode I notice that I never mentioned her last name, and it sounds kinda odd.

2. Or perhaps more accurately have a very limited ability to do this. I’ll put it this way: if I were to stick you on an Earth-like planet with plenty of water and all the grass you could eat – actually let’s just make it cellulose, because technically cereal grains are part of the grass family – you would die within a month. You might make it over the one month period if you were to do like rabbits do and eat your own poo. That’s right. Rabbits eat mostly plants, but they are not ruminants so they are forced to eat their droppings because they will digest and absorb more energy in a second pass since cellulose is so difficult to break down.

3. At least here in the United States

4. or a corn/hay mix

5. Russell JB, et al. (2000) Invited Review: Effects of Diet Shifts on Escherichia coli in Cattle. J Dairy Sci. 83:863-873

6. There’s an exceptional documentary called King Corn that I highly recommend if you would like to know more about corn, why it is so pervasive as a feed, and what the implications are regarding beef and simply food in general. The short version is the US government subsidizes corn farming, encouraging a surplus of cheap corn on the commodities market. This has a double bonus for cattle farmers giving them not only cheap feed but also a feed that fattens cows much quicker and easier than grass. However, corn has a major downside of making the cows very sick. Just watch the film.

7. Daley CA, et al. (2010) A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutrition Journal. 9:10

8. Houseknecht KL et al. (1998) Dietary Conjugated Linoleic Acid Normalizes Impaired Glucose Tolerance in the Zucker Diabetic Fatty fa/fa Rat. Biochemical and Biophysical Research Communications. 244:678-682

9. Lee KN, et al. (1994) Conjugated linoleic acid and atherosclerosis in rabbits. Atherosclerosis. 108:19-25

10. Akoh CC. (Ed.) (2006) Handbook of Functional Lipids. Boca Raton, FL: CRC Press. p. 363-364

11. Akoh CC. (Ed.) (2006) Handbook of Functional Lipids. Boca Raton, FL: CRC Press. p. 364-381

12. Shils ME and Shike M. (2006) Modern Nutrition in Health and Disease. Philadelphia: Lippincott Williams & Wilkins. p. 1727