Protein wars flare again 
12 February 2020

Based on our anatomy, humans are omnivores. Due to the abundance of food, in many wealthy countries, one of our biggest dilemmas is what to eat?

There are essentially 3 macronutrients – fat, carbohydrate and protein (while it provides energy, alcohol does not meet other criteria for being a macronutrient).

Fats were demonised in the 1980’s and 1990’s, carbohydrates (starches and sugars) in the 2000’s and 2010’s. Now its protein’s turn.

Over the past ~12 months, meat eaters, vegans and their associated commercial interests, have been battling it out in both the popular media and in scientific journals, arguing over the health and environmental effects of their favoured protein sources.

Hot on the heels of the series of studies published in Annals of Internal Medicine in October 2019, which found that the association between red and processed meat consumption and all-cause mortality and adverse cardiometabolic outcomes is very small, this latest battle in the protein wars published in the Journal of the American Medical Association investigated the association between eating processed meat, unprocessed red meat, poultry, or fish and the risk of developing cardiovascular disease (fatal and nonfatal coronary heart disease, fatal and nonfatal stroke, fatal and nonfatal heart failure, and other CVD deaths) in a pooled cohort of 29,682 North American (USA) adults.

Food frequency questionnaires were used to assess participants intakes of these protein sources at baseline only. Methods of preparation or cooking were not included in the analysis. Participants were followed up for up to 30 years. The overarching finding was that higher consumption of processed meat, unprocessed red meat, or poultry, but not fish led to an approximately 3% to 7% higher relative risks and less than 2% higher absolute risks of incident cardiovascular disease and all-cause mortality (death) over the 30 years of follow-up.

Like the Annals of Internal Medicine studies, the effect sizes of these association estimates are small, and consequently at high risk of confounding despite multiple statistical adjustments. In observational studies, if relative risk is less than 20%, the results are not considered to be strong, and are likely confounded – despite statistical adjustment for known confounders, there are potentially a large number of unknown/unmeasured confounders.

So, while the results of this pooled analysis are interesting, they do not constitute high-quality scientific evidence. Some commentators have suggested that even though the associations are small, when applied across the whole population, it still means fewer people will develop heart disease or die from eating too much processed meat, unprocessed red meat, or poultry. Unfortunately, the results are not strong enough to draw these conclusions.

Serious weaknesses include the fact that few people maintain exactly the same eating habits over a 30-year time frame due to ageing, and associated life-stage changes (e.g., rearing children). How the meat/poultry/fish were cooked is also very important. Was the chicken grilled, or battered and deep fried as is common in many parts of the USA? Grilled chicken is healthy, battered and deep-fried chicken isn’t.

This study does not merit the attention it has been given in the popular media. It will only add more fuel to the fire, pitting vegan/plant food activists against their omnivorous cousins. The only winners will be proponents of the latest fad diets and food industry that is hoping to cash in on people’s ignorance.

Vegan burger anyone?

Oh, and I can’t wait to read Meat poison and I quit animals.