Wednesday, October 20, 2010

Scientists and Statements Unsupported By Evidence

My friend Mike Lieberman posted this interesting link earlier today, about a fellow who discovered what he thought to be grass-fed beef actually wasn't.

"The real question that is bugging me now is the bottom line: is grassfed healthier? I recently read this article by a real scientist who, although he has no problem with grassfed beef, wishes to dispel myths about it. He claims that grass-fed cattle actually cause a bigger negative impact on the environment than factory farmed cattle because of overall carbon emissions, and he claims that the CLA and omega-3 benefits of grass-fed beef are null and void once cooked. I haven’t done any research into his research, but I’m definitely curious to hear what others think."

Well, unfortunately a PhD does not mean you're a "real scientist".  The credentialed, but uneducated are a plague upon our society, and many of them claim to be scientists.  Giving people the benefit of the doubt no longer seems to be a viable alternative, either.

So let's examine the statements that troubled Kitchen Stewardship, from Dr. Comerford (emphases mine):

"The ‘potent anti-carcinogen’ CLA story may be one of the biggest hoaxes played on the consumer because the values used to differentiate grass-fed from grain-fed beef are from raw meat. Samples of raw grass-fed beef consistently have twice the CLA content as a proportion of total fat than samples from raw grain-fed beef. This means the typical grass-fed steak has the same CLA content as a Certified Angus Beef ®, heavily grain-fed steak because there would typically be twice as much total fat in the CAB steak. However, this is all irrelevant because studies show when the meat is cooked, there is no difference in CLA content because a large amount of the fat is lost in cooking. Even if people ate the meat raw, you would have to eat 176 pounds of grass-fed beef daily to get the level fed to the mice in the original CLA study (Ha et al, 1987). It also should be noted that in the original CLA study 16 of the 20 mice getting huge doses of CLA still got cancer. The dosage of CLA from this study would have to be increased 182,000 times for an equivalent dose to an average person. The whole CLA story has been based on these 4 mice, making this result irrelevant to human health.

His statement about the ratio of CLA in grass-fed to grain fed appears to be correct.  However, the other important difference between the two is the ratio of omega-3 to omega-6 fats.  The grain-fed Angus may have the same amount of CLA, but it would have a far higher amount on omega-6 linoleic acid, which is well-recognized as having many negative effects on human health.  So making up for your missed CLA by eating grain-fed Angus is clearly not a good idea.  Oh, and if you spend a few moments looking over the research on CLA, you'll find it constantly described as a 'potent anti-carcinogen', and there are a lot more studies than just the one that Dr. Comerford mentions.

His statement: “However, this is all irrelevant because studies show when the meat is cooked, there is no difference in CLA content because a large amount of the fat is lost in cooking.” just appears to be false:

“The major changes in fatty acid composition, which implicated 16 out of 34 fatty acids, resulted in higher percentages in cooked beef of SFA and MUFA and lower proportions of PUFA, relative to raw meat, while conjugated linoleic acid (CLA) isomers revealed a great stability to thermal processes. Heating decreased the PUFA/SFA ratio of meat but did not change its n−6/n−3 index. Thermal procedures induced only slight oxidative changes in meat immediately after treatment but hardly affected the true retention values of its individual fatty acids (72–168%), including CLA isomers (81–128%).”

Meat Science, Volume 84, Issue 4, April 2010, Pages 769-777

In other words, the polyunsaturated fatty acids ooze out of the beef to a small degree.  Dr. Comerford doesn't explain why this would happen to a greater degree in grass-fed rather than grain-fed beef.

Similarly, this document, titled "Conjugated Linoleic Acid and Dietary Beef" from the National Cattlemen’s Beef Association states: "CLA in meat is stable under normal cooking and storage conditions."

Dr. Comerford goes on:
"Similarly, the Omega-6 to Omega-3 fatty acid ratio is an important feature of fat intake in humans. The recommended daily intakes of Omega-3 fatty acids from the World Health Organization of 1.1 to 1.6 grams/day show it would require a person to eat 4 1/2 pounds of cooked grass-fed beef daily to meet the minimum daily requirement. Therefore, any speculation that eating grass-fed beef will enhance human health due to Omega-3 fatty acid consumption is clearly incomplete at best, and usually false."

Again, no evidence provided to support the statement. 

Now, this page states that the WHO actually recommends 0.2 to 0.5 gram per week of omega-3 [corrected] fatty acids.  That's a half pound to 2.25 pounds a week of beef.  One quarter-pounder of grass-fed beef per work day and you're good to go for your omega-3 [corrected]; not 31.5 pounds of beef a week.

Dr. Comerford may well be the only beef specialist who believes this particular statement, in fact:

"The data obtained from this study demonstrate that high grass intake resulted in a higher polyunsaturated fatty acid (PUFA):saturated fatty acid ratio and a lower n-6:n-3 PUFAratio in intramuscular fat of steers than in that of similar steers fed concentrates. Moreover, a higher concentration of conjugated linoleic acid was observed for grass-fed steers than for steers fed silage and(or) concentrates, when grown at similar carcass growth rates. These data imply that the fatty acid profile of intramuscular fat in beef can be improved from a human nutrition perspective by the inclusion of grass in the diet."

Also, he does not discuss the difference in the ratio of n-3 to n-6 fatty acids in grass-fed vs. grain-fed beef. We know that high intake of n-6 fatty acid (linoleic acid specifically) is linked to weight gain and cancers in animals and humans. Wouldn’t eating foods reflecting a more normal balance of n-3 to n-6 seem wise in light of that?

The primary problem is that linoleic acid consumption is cumulative, so if you're always eating excess amounts of it, it will add up.  You will eat a little bit everyday, as it's a normal part of our diet.  But you want to minimize its consumption.

So I don't know what's up with this fellow.  I found another comment he made:

"Dr. John Comerford wrote on Jun 1, 2009 11:06 AM:

"We in the academic community should be very careful crediting grass-fed beef as a healthy product to humans. I am a preponent of the product, but I also know there is no scientific evidence to support grass-fed beef as any more healthy to humans. The one exception is possibly the Omega-6: Omega 3 ratio in the fat, but we also know it will take SIX raw quarter-pounders a day to meet the MINIMUM RDA of Omega-3 fats. After they are cooked, it will take even more because of the loss of the fat in cooking. This is also the problem with CLA in this product. There is very little there in the raw product and it is nearly eliminated by cooking, while the only clinical data related to health used 100 times the amount in the raw product. Let's stick to the important-and true-stuff. It is local, it is produced in a pasture environment, and it promotes the use of grasslands. These are features consumers will pay for. "

Guess what the Recommended Daily Allowance of meat-based omega-3 fats is?  Zero.  That's right, there is no RDA for meat-based omega-3 fats.  I'm beginning to think this guy is just making it up as he goes along.

P.S.: Got the omega-6 mixed up with omega-3 above.  Marked where corrected.