When we read about the latest study on red meat, performed at UC San Diego and published in the Proceedings of National Academy of Sciences,1 we were a bit taken aback. Claims about the safety of red meat based on a laboratory experiment with mice seemed like a pretty enormous leap.
Dr. Roger Clemens,
To take a closer look, we enlisted the help of one of an expert: Roger Clemens, DrPH, CFS, CNS, FACN, FIFT, FIAFST, Adjunct Professor of Pharmacology & Pharmaceutical Sciences at the USC School of Pharmacy International Center for Regulatory Science. Dr. Clemens reviewed the paper thoroughly, along with all of the references cited and 12 additional publications on Neu5Gc (the sugar that was studied). Then he very patiently took all our questions and helped us make sense of some of the more eyebrow-raising claims.
For background, the study looked at the role of a unique sugar-like substance called Neu5Gc, which is naturally found in most mammals but not in humans. Mice were engineered to be deficient in Neu5Gc (which humans naturally lack). They were then fed the sugar, which the authors assert “significantly promoted spontaneous cancers.”
FACTS Network: How does this study fit with what we already know about red meat?
Dr. Roger Clemens: Every food contains at least one compound that may pose a health hazard at some level of intake. When eaten in a typical quantity and with other foods, virtually none of these compounds present a health risk. No studies have implicated Neu5Gc as a potential health risk. It is interesting to note that Neu5Gc antibodies appear to be important for humans to combat a variety of viral infections. There is also evidence that without this unique sugar, there is an increased risk of GI infections among humans.
FACTS: Are there any issues with using mice to extrapolate health conclusions to humans? How does the quantity of Neu5Gc that was consumed by the mice fit with the amount we consume as humans?
RC: Based on some quick calculations of the dose and animal model, it looks like the studied mice were fed an amount nearly 100 times (per kg bw) larger than any potential dietary exposure by humans. Also, this dose was consumed daily for about 50% of the typical lifespan of the mice. For comparative purposes, it is unlikely that humans would consume “beef” (which has the highest concentration of Neu5Gc) daily for half their life expectancy.
It would have been useful to translate the data into practical exposure of Neu5Gc, based on how much different people actually include in their diets. The study does not provide any insights to this important aspect of exposure.
FACTS: What might be the effect of isolating Neu5Gc from meat and delivering it in an isolated form? Does this impact how you view the conclusions?
RC: Looking at the references from the study and other studies to date on Neu5Gc, none addresses how this unique sugar would actually operate within the food and within the diet.
FACTS: What might be the effect of engineering mice to not produce the sugar, whereas they would usually produce it naturally?
RC: The use of “genetic knockout” animals (animals in which one their genes is made inoperative) can be a useful model to understand metabolic consequences. However, this study does not readily address the genetic variations in mammals and the tissue distribution of Neu5Gc in these animals. It’s therefore difficult to know how it might affect conclusions, since the biological accumulation of New5Gc varies among species and tissues within a given species.
FACTS: What do you recommend consumers do regarding their consumption of red meat?
RC: The 2010 Dietary Guidelines for Americans noted that red meat can provide a variety of important nutrients, particularly among populations at risk (women who are or may become pregnant, children, and seniors). There’s no reason to cut out a food with valuable nutrients.
Big picture, it is important that consumers’ dietary patterns include a variety of foods, including fruits and vegetables. The picture of Neu5Gc and inflammation remains unclear and controversial.
To sum it up, while this study raises some interesting questions for future research on the unique Neu5Gc sugar in red meat, saying that this substance promotes inflammation or cancer at the current dietary consumption levels is a leap that’s completely premature.
1. Annie N. Samraj, Oliver M. T. Pearce, Heinz Läubli, Alyssa N. Crittenden, Anne K. Bergfeld, Kalyan Banda, Christopher J. Gregg, Andrea E. Bingman, Patrick Secrest, Sandra L. Diaz, Nissi M. Varki, and Ajit Varki. A red meat-derived glycan promotes inflammation and cancer progression. PNAS, December 2014 DOI: 10.1073/pnas.1417508112