This article by Eoin O’Connell reports a study in the American Journal of Clinical Nutrition (the top nutrition journal) that found a correlation between meat consumption and weight gain: The more meat you ate, the more weight you gained over five years. Meat is fattening! reported several newspapers.
Mr. O’Connell did something unusual for a health journalist: He thought for himself. I don’t mean he applied a formulaic criticism (e.g., “correlation does not equal causation”). That’s not thinking, that’s knee-jerking. Mr. O’Connell read the paper. And he noticed an interaction: The correlation between meat consumption and weight gain depended on activity level. The study involved about 400,000 people. The researchers put each person in one of four activity levels: inactive, moderately inactive, moderately active, and active. There was a correlation between red-meat consumption and weight only for the two most active groups (moderately active and active). The original article reported that this interaction was significant:
The relation between red meat and weight gain was also stronger in physically active subjects compared with moderately inactive or inactive subjects (P values for interaction = 0.02)
The obvious implication of this interaction, as Mr. O’Connell says, is that meat caused muscle gain. Weight differences between more-meat and less-meat eaters were due to differences in muscle mass. This puts an entirely different spin on the results. The alternative explanation is quite plausible. I once had a grad student who was a vegetarian. When he was an undergrad, he told me, he and his roommate would go to the weight room and do similar sets. His roommate, who ate meat, rapidly gained muscle; he did not. Of course, meat = animal muscle.
Mr. O’Connell continued to the really interesting part of his article:
Perhaps not so surprisingly, the consideration that muscle is a form of weight gain does not appear in the newspaper articles but much more surprising is the fact that it does not appear in the original journal article either.
The AJCN article has fifty authors. Not one of them, apparently, noticed this all-important point! Nor did the reviewers for this prestigious journal. The article concludes: “Our results are therefore in favor of the public health recommendation to decrease meat consumption for health improvement.” No, they’re not, if the more meat, more muscle explanation is correct.
Most prestigious journal. Fifty authors. Huge expense. Total F-up in the sense that the final conclusion is probably wrong. (To be fair, the paper has plenty of value in other ways.) Congratulations, Mr. O’Connell, for noticing.
It’s a good example of how lazy the thinking and methodology of scientists can get once prejudices are well established. Red meat is seen as suspect and weight gain is assumed to be fat mass gain. It would have been nearly as easy to measure change in waist circumference, which would have given a better indication of metabolic risk. The conclusion is applied generally to “weight management”, when all they’re justified in saying is that active people could consider reducing red meat intake if they want to maintain a lower overall body mass. They could also conclude that inactive people shouldn’t worry about their red meat intake’s effect on their mass, but that wouldn’t chime with public health prejudices. The incentive to bolster the public health message appears stronger than the scientific spirit, unfortunately.
Good catch! This is a great post!
Great find. This is the danger of only assessing weight rather than looking at body fat percentage. i believe the science has evolved enough to be able to use this measurement rather than weight or BMI. especially when exercise is involved in the intervention.
Apparently this point never occurred to the people who came up with BMI either. I am 6’1 210 pounds but a competitive Olympic Style Weightlifter. I come up as overweight just like the other guy who is 6’1 210 pounds, sits on his couch all weekend watching reruns and hasn’t done any exercise since 6th grade PE.
@Thomas, Agreed! It’s like measuring a bag of nickles to determine how rich you are. Doesn’t matter if they’re real copper-nickle clad nickles or lead-wood fake nickles. Same logic should be levied at standard calculations of BMI which is agnostic to where the weight is coming from, fat versus muscle (it’s both, of course, but the ratio is what really matters and is not determinable from conventional measures).
i don’t quite understand though – why is more muscle not as bad as more fat?
obesity is almost always due to lots of fat, not lots of muscle. obesity is correlated with higher risk of many health problems.
This is a great catch, Seth! Too bad more journalists weren’t like this.
Thank you for this post, Seth! Amazing …
Definately food for thought! I am trying to gain weight at the moment and it isn’t easy; so any related info’ is much appreciated! I have been charting my (minimal!) progress on my blog https://www.underweight-arewewhatweeat.blogspot.com
Logical inconsistencies abound in medical literature, don’t they. How bout the cholesterol myth and the fat makes you fat myth. Mark at MDA just posted today about how CLA supplements aren’t beneficial after all. Seriously, the nutritional scientists don’t know what they’re doing most of the time.
I think finding a wholly valid, well executed study would be a bigger feat!
“That’s astounding. Fifty authors and nobody caught that… Wow.”
With 50 authors, I expect there was a 3- or 4-level hierarchy within the project, and a big budget. So, you can imagine an underling being afraid to criticize his boss and boss’s boss, people he’s unlikely to have collegial relations with. A more senior author (“manager” is perhaps the accurate term) might not want to risk discrediting the whole effort and earning the wrath of his peers (again, people he may not have true collegial relations with).
I wonder if a team of 15 might be more likely to self-correct, since team members (even of different ranks) might be more likely to know and respect one another.
Christopher, yes, psychologists have studied this sort of thing. The effect is called “diffusion of responsibility”. The more people who might take action (such as point out a mistake) the more passive each person becomes.
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In defense of the 50 authors, probably 40 of them never read the article they authored