Eating Protein As Harmful As Smoking? What?

March 12, 2014

Last week, a study was published in Cell Metabolism that was titled “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.” Without reading the actual study, it would be easy to come to the conclusion that high protein diets would contribute to increases in cancer and overall mortality in those younger than 65. In fact, media has taken the study’s title and summary and run with them creating articles such as “It’s time to kick the high-protein diet habit – before it kills you,” “High-Protein Diets in Middle Age Might Shorten Life Span,” “Now we can’t eat protein. What can we eat?” and our favorite “Diets high in meat, eggs and dairy could be as harmful to health as smoking”…. Wow. Those are pretty sensational titles for articles. It’s time tone it down a notch, see what was actually found in the study and what other research has also said.

We could delve deep into the science using all kinds of terms discussing the different kinds of research and statistical models used to interpret data, but we won’t. Instead here is the abstract from the actual published study:

“Mice and humans with growth hormone receptor/IGF-1 deficiencies display major reductions in age-related diseases. Because protein restriction reduces GHR-IGF-1 activity, we examined links between protein intake and mortality. Respondents aged 50–65 reporting high protein intake had a 75% increase in overall mortality and a 4-fold increase in cancer death risk during the following 18 years. These associations were either abolished or attenuated if the proteins were plant derived. Conversely, high protein intake was associated with reduced cancer and overall mortality in respondents over 65, but a 5-fold increase in diabetes mortality across all ages. Mouse studies confirmed the effect of high protein intake and GHR-IGF-1 signaling on the incidence and progression of breast and melanoma tumors, but also the detrimental effects of a low protein diet in the very old. These results suggest that low protein intake during middle age followed by moderate to high protein consumption in old adults may optimize health span and longevity.”

In a nutshell, this was an epidemiological study using pre-existing survey data that assessed 6381 adults over the age of 50, which was then backed up with rodent studies. The data in the survey was all self-reported, as well as no lifestyle data being included and neither was the type of meat product. This leaves many questions unanswered. There are certain things we know through previous research that contribute or take away from the findings of this study that were not discussed or investigated.

Some things to consider and think about:

  1. Exercise effects
  2. Animal protein source –processed vs unprocessed. Chicken breast, fish and lean red meat versus processed meats (bologna, ham, hot dogs, bacon – yes, sorry bacon) and fast food sources. Certain additives have been shown to be carcinogenic while certain processes have also been shown to create carcinogens.
  3. What about those younger than 50?
  4. Fruits and vegetables? The study only looked at carbohydrates, fat and protein as percent of calories contributed.
  5. In the low protein group what was used to make up for the difference in calories? Did it have protective effects?
  6. What about fast food versus home cooked meals?
  7. Healthy lifestyle was not considered, only dietary intake of macronutrients (fat, carbohydrates and protein).
  8. Overall mortality – protein intake is related to overall mortality? There are so many other things relating to overall mortality such as obesity, breathing, smoking, alcohol, driving…

Protein intake directly influences IGF-1 levels. Causation was proven in rodents through dietary modification (decreasing protein in their diet) when there was a 78% reduction in tumor size. This was used to indirectly support the role of IGF-1 in humans. In humans IGF-1 causes cell growth. It acts on all cells regardless of them being cancerous or not. Decreasing levels of IGF-1 in patients with cancerous tumors could slow, inhibit or reverse the growth of the tumors. In this study ALL of the rodents were implanted with tumors. It is generally thought that IGF-1 promotes the growth of pre-existing tumors, not cause them. So with the implantation of the tumors it confounds the study.

The Take Away

It is important to look at the actual studies and not just at the interpretations the media provide. All too often we end up missing the complete story because we focus on the sensational headlines and the tidbits used to back them up.

The actual researchers addressed some of the considerations I mentioned above. Here is the web address where you can find the published research and the researchers addressing the considerations in its’comment section:


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