What the new studies REALLY say about red and processed meat

New studies this week in the Annals of Internal Medicine have generated much fiery news coverage.

For example, Time's headline says: "Should You Stop Eating Red Meat? A New Paper Has a Controversial Answer." As always, the nutrition reporter portrays nutrition science as fickle, endlessly reversing itself.

It's not true. The actual scientific content in the new studies confirms what we already knew.

The best available evidence suggests that reducing red and processed meat consumption will reduce risk of death from cardiovascular disease and cancer.

It always is the case that nutrition scientists and communicators must accomplish two tasks: 

1. understand the available evidence; and 
2. reflect on what burden of proof should be used for nutrition policy decision making.

The new studies made atypical decisions about Task #2. For reasons that are not clear to me -- perhaps out of a scientific sense of caution or perhaps out of a bias in favor of red and processed meat -- they ramped up the burden of proof that they apply to recommendations that advise less red and processed meat. Citing research guidelines that give highest scores for pharmaceutical trials [edited slightly 4pm], they rate most of the available evidence in any direction as weak. This is not how I would have communicated the evidence. In my view, it is understandable that randomized control trials cannot be widely used on this topic, because one would have to wait too long for a sufficient number of cancers or heart attacks attributable to a meat intake intervention in a well-powered study. So, I have long accepted cohort and observational studies as the best available evidence on this topic. The new studies do pretty much the same, but they label each piece of evidence as "weak." They are free to apply these labels, and I feel free to ignore these labels.

Turning to Task #1, the studies confirm what I already knew. For example, here are my statistical interpretation sentences for several main results from the new studies.

On average, reducing weekly unprocessed red meat intake by 3 servings is associated with:

• 7% lower risk of death, 
• 10% lower risk of death from cardiovascular disease,
• 6% lower risk of stroke,
• 10% lower risk of type 2 diabetes,
• 7% lower risk of death from cancer.

The list of results continues for processed meat.

If you want to describe these effects as "small" and you want dietary changes that reduce your risk by twice as much, then knock yourself out. You may reduce your red meat intake by perhaps approximately [note: qualifying adjective added 4pm] 6 servings.

I recognize that these results are accompanied by blistering disparagement of recommendations to eat less red and processed meat, but I don't trust these authors enough to place credence on their rhetorical choices. Their scientific results are what matters. 

Reading these scientific results, even acknowledging the limits of our knowledge, I will continue to support existing recommendations to eat less red and processed meat. No better evidence exists.

Processed meat labels saying "uncured" and "no nitrites added" are misleading

A large body of evidence reviewed by the World Health Organization found that processed meat consumption increases the risk of cancer. Seeking to alleviate consumer concern, food companies label some of their products as "uncured" or "no nitrites added." However, these products may have essentially as much nitrites or nitrates as regular products.

In an August 29 report from Consumer Reports (CR), policy analyst (and Friedman School Ph.D. student) Charlotte Vallaeys explained the issue.

“Thanks to the topsy-turvy world of government food labeling rules, ‘no nitrites’ doesn’t mean no nitrites,” says Charlotte Vallaeys, senior food and nutrition policy analyst at CR. Instead, it means that the nitrates and nitrites used to “cure”—or preserve and flavor—meat come from celery or other natural sources, not synthetic ones, such as sodium nitrate or nitrite.

The issue was picked up in August by NPR in a report by Allison Aubrey.

This issue also is the subject of a new citizen petition from the Center for Science in the Public Interest (CSPI) and Consumer Reports, which in turn led USDA to open a public comment period until Nov. 12.

Meanwhile, I remain concerned that the federal government's Dietary Guidelines for Americans (DGA) for 2020-2025 may overlook scientific evidence on processed meat and cancer risk. It is important for USDA and DHHS to review this evidence directly, as its own topic, not just tangentially when it arises as part of broader studies of dietary patterns. That scientific issue was covered in a blog post in early August, noting our recent article in Milbank Quarterly.

In related work, my colleague Dr. David Kim and several co-authors and I have a new article in the American Journal of Preventive Medicine (AJPM), published today, with a modeling analysis of the health benefits that could arise if warning labels or a tax on processed meat effectively reduced intake and thereby reduced cancer risk. The abstract concludes:

The model shows that implementing tax or warning labels on processed meats would be a cost-saving strategy with substantial health and economic benefits. The findings should encourage policy makers to consider nutrition-related policies to reduce cancer burden.

Dietary guidelines, processed meat, and risk of cancer

In a public comment submitted today, my colleagues Fang Fang Zhang, Jennifer Pomeranz, and I encourage the 2020-2025 Dietary Guidelines Advisory Committee (DGAC) to evaluate the entire scientific literature on processed meat and colon cancer risk.

The DGAC is the external committee that summarizes the scientific evidence on nutrition and health, which two federal departments, USDA and DHHS, then use in writing the actual Dietary Guidelines for Americans, an influential document in U.S. nutrition policy.

USDA and DHHS have determined that the 2020-2025 DGAC may only address topics that were explicitly given in a list of questions by the departments.

One of the questions is: "What is the relationship between dietary patterns consumed and risk of certain types of cancer?"

Our public comment today recommends that the DGAC include the entire scientific literature on processed meat and cancer risk, as part of its systematic review of evidence on dietary patterns and cancer.

Why is this even in doubt?

As our recent article in the Milbank Quarterly recounts, in the previous 2015-2020 Dietary Guidelines for Americans, the federal government muddled its message on processed meat and cancer.

On the one hand, it included lower intake of processed meat in a list of characteristics of healthy eating patterns: "Lower intakes of meats, including processed meats; processed poultry; sugar-sweetened foods, particularly beverages; and refined grains have often been identified as characteristics of healthy eating patterns."

On the other hand, it said that processed meats can be recommended as long as sodium, saturated fats, added sugars, and total calories are within limits. This latter favorable comment in the official policy document from USDA and DHHS had no basis in the earlier independent scientific report from the 2015-2020 DGAC.

Even though it is not responsible for the final DGA report, we think the 2015-2020 DGAC report may have overlooked some of the important research on processed meat and colon cancer, by interpreting the words "dietary patterns" too strictly, screening out some research on processed meat merely because this one food category is not a "dietary pattern."

Why is the cancer risk from processed meat important?

The issue is important because the best available systematic literature reviews concluded that consuming processed meat increases the risk of colon cancer. In particular, see authoritative reports from the International Agency for Research on Cancer and the World Cancer Research Fund and American Institute of Cancer Research.

Luxian Zeng, Fang Fang Zhang, other colleagues, and I recently reported in the Journal of the Academy of Nutrition and Dietetics (JAND) on trends in processed meat intake based on data from the Nutrition and Health Examination Survey (NHANES). While red meat declined, processed meat held steady in recent years. This issue is big enough to matter for national nutrition policy.

What are the policy implications of ignoring this issue?

Currently, far from encouraging reductions in processed meat intake, the federal government supports advertising and marketing programs to increase consumption. The semi-public checkoff programs have been covered previously in this blog. Just to give one current illustration, here is advertising from the federal government's pork checkoff program for bacon and ice cream. If the Dietary Guidelines for Americans were based on a full evaluation of the scientific literature about processed meat and colon cancer, it might facilitate policies to encourage reductions, or at the very least a halt to these advertising programs encouraging yet more processed meat consumption.

National Pork Board advertising endorsed by USDA.