{"id":3696,"date":"2019-10-11T16:46:05","date_gmt":"2019-10-11T23:46:05","guid":{"rendered":"https:\/\/fueledbyscience.com\/?p=3696"},"modified":"2019-10-21T20:58:07","modified_gmt":"2019-10-22T03:58:07","slug":"red-meat-healthy-harmful-or-harmless","status":"publish","type":"post","link":"https:\/\/fueledbyscience.com\/red-meat-healthy-harmful-or-harmless\/","title":{"rendered":"Red Meat: Healthy, Hazardous, or Harmless?"},"content":{"rendered":"\t\t
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\"\"Should you eat less red meat? Why or why not?<\/p>\n

The latest study on red meat and health concluded that the potential health benefits of reducing red meat are too small, and the\u00a0strength of evidence too weak, to justify current dietary recommendations.\u00a0<\/p>\n

Health experts around the world are pushing back, calling these conclusions “reckless” and “irresponsible”. What’s going on?\u00a0<\/p>\n

Beneath the headlines, the latest study reads like a familiar story\u2026until the last chapter. It turns out that the debate is in large part about the bigger question of how we should approach dietary guidelines.<\/p>\n

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What type of studies were done?<\/h3>\n<\/div>\n

The news headlines stem from a collection of five meta-analyses – studies that analyze existing data, in order to summarize overall trends [see lead research article by Johnston, BC et al<\/a>]. The five studies were limited to human data, and included many large observational studies as well as one randomized controlled trial. Each study compared rates of disease and death from common conditions (cancer, cardiovascular disease, and diabetes) in those who consumed more red meat (either processed or not) to those who consumed less red meat.<\/p>\n

What did they find?<\/h3>\n

In many ways, the findings were familiar: those who ate less red meat tended to have a lower risk of disease and death.<\/p>\n

Greater red meat intake was consistently linked to higher overall death rate, cardiovascular death rate, and risk of type 2 diabetes.\u00a0In most cases, the risk reduction was on the order of 10%-15% lower for substantial dietary changes (e.g cutting back red meat consumption by three portions per week). \u00a0Whether or not this benefit is “small’ depends on your perspective.<\/p>\n

The most notable divergence from past reviews was in the link between red meat and cancer. The link was much weaker than I (and others) expected, and only showed up between processed red meat and overall cancer. It was particularly surprising not to see support for a link to colorectal cancer – even for processed red meats.<\/p>\n

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How Did The Authors Evaluate the Quality of Evidence?\u00a0<\/h3>\n

The authors used the GRADE framework for ranking evidence, one that was developed for clinical decision making. This framework ranks all observational studies, in which we observe people’s diets but don’t control them, as “low”. Such studies are, for better or for worse, the bread and butter of nutritional science.<\/p>\n

The rationale for this grade is that “correlation does not equal causation”. In other words, associations can’t prove a causal link because confounders might be the real reason for the link.\u00a0For example, those that eat more red meat may be less healthy because they are less health-conscious in general and may be more likely to smoke, more overweight, etc. We can partially control for these factors using statistical methods, but it’s virtually impossible to do this perfectly.<\/p>\n

Same Story, Different Ending<\/h3>\n

The biggest criticisms of this latest study relate to how they are translated (or not) into dietary recommendations. The three big issues are:\u00a0<\/p>\n

1. Which types of benefits matter? Individual health, public health? Other benefits?<\/b><\/p>\n

The authors have been criticizes for their lack of consideration for potential public health benefits, as well as their assumptions about the inherent lack of desirability of dietary change.<\/p>\n

The authors emphasize the importance of considering changes in absolute disease risk, not just relative disease risk. Indeed, a 10% reduction in disease risk (relative risk) sounds a lot more impressive than a drop from 5% to 4.5% risk. While this distinction is important, it fails to recognize that even small individual risk reductions\u00a0\u00a0(e.g. 5 fewer cancer cases out of 1,000)\u00a0can be very meaningful at a national and global scale. It’s no surprise that organizations with public health interests push hard for even small potential benefits.<\/p>\n

Furthermore, the study has come under fire for failing to appropriately consider\u00a0other implications of food choices (e.g. sustainability and animal welfare). Whether or not these issues are in scope for dietary recommendations is a matter of debate.<\/p>\n

2. Which types of data are relevant to dietary recommendations<\/b>?<\/p>\n

The studies have been criticized for their narrow scope. They authors only considered data from human studies, and further limited the studies to trials that met stringent inclusion criteria. While this filter has the upside of avoiding “noisy” data that come with many caveats, the result is an incomplete picture.<\/p>\n

\u00a0Notable excluded data include:<\/p>\n