I received questions/comments from three different people about a recent article from The Wall Street Journal, which referenced a recently released study (actually, one of the emails was from a former student who lives in Australia, after she saw a similar article in The Sydney Morning Herald, a few days prior to the WSJ article publication).
The WSJ article, titled ‘The Risk of High-Protein Diets: Two studies indicate that they may do harm than good’, was released early this week, and referenced two studies, one of which I pulled and will comment on here (ME Levine et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metabolism. 19: 407-417, March 4, 2014).
After reading both the WSJ article and the actual research article, I have to say that the author of the WSJ article, Kevin Helliker, did a great job with both the article and the title of the article in terms of conveying information from the study (the Australian version, not so much, the title was a bit more sensationalistic: ‘High-protein diet a factor in shorter life.’)
Therefore, I needn’t waste time evaluating both, so I will get to the heart of it, and try to point out a few red-flags as I go.
First off, the study was conducted as a survey (as most nutritional studies are), therefore the ‘subjects’ were more accurately described as ‘respondents.’ Here is would be prudent to point out a minor red-flag: when relying on the recall/memory and or reporting of behavior by subjects, there is always the potential for error.
The average age of the group was 65 years; the population was indicated as representative of the US population in terms of ethnicity, education, and health; and the average caloric intake of the group was 1,823 calories (51% carbohydrate, 33% fat, 16% protein).
The survey group was divided into a high-protein group (20% or more calories from protein), moderate-protein group (10-19% of calories from protein), and a low-protein group (less than 10% total calories from protein).
The follow-up period for the dietary and mortality analysis was 18 years, and initial results showed that for the population as a whole, there was no correlation between moderate-to-high levels of protein intake and all-cause mortality, cardiovascular disease mortality, or cancer mortality (there was an association between high protein intake and diabetes mortality, paradoxically).
However, when the overall sample was split by age (a 50-65 year old group and an over 65 years old group), the results changed. The younger group did have a positive correlation between increased protein intake and all-cause or cancer mortality, with animal protein showing to contribute significantly.
Conversely, the older group (66+) saw the opposite trend, with the high-protein group having a 28% reduction in all-cause mortality compared to the low-protein group. A possible explanation offered for this is that older individuals have greater difficulty digesting protein, and therefore a percentage of it does not even make it into the blood stream.
So what does it all mean? There is an explanation offered regarding the effect that protein consumption has on a few key hormones, and I will spare you that for this week! (Cliffhanger….)
But when I read this, the questions I have involve things that are unknown based on the research report, and specifically something that was probably unknown to the researchers as well- what were the specific protein sources?
Were these subjects eating factory-produced meat, or were they eating naturally produced meat? Because that will make a big difference! Based on the fact that the respondents were comprised of ‘average-Americans’, I would venture to say that the majority participated in the industrial food system.
Were there other confounding factors that were unreported? Did any of them smoke? Drink? Participate in regular physical activity? We just don’t know. And that can leave a lot of questions about the final conclusion of this study.