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 nutritionbycarrie.com.
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
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.
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 http://www.ncbi.nlm.nih.gov/pubmed/21070685
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