Does eating red meat increase the risk of heart disease? Will eating more vegetables help? Is leaving high blood pressure untreated really a death wish? Answers may vary depending on who one asks, which TikTok friend or nurse, and when. University of Washington researchers want to make it easier to find up-to-date, evidence-based health advice.
A new tool from the Institute for Health Metrics and Evaluation, presented Monday in Nature Medicine, uses a 5-star rating system to indicate how much evidence exists to support certain dietary and lifestyle changes. The researchers analyzed hundreds of studies in hopes of helping consumers, clinicians and policymakers — mired in a landscape of health influencers, food lobbyists and advice quacks — cut through the chatter and discern the scientific consensus. The result is what they call “burden of proof studies,” because the research has to prove that something is legitimate.
Other similar reviews exist, and the Cochrane Library is a repository for many of them. This new tool, the authors say, complements the existing one, but it’s also a bit different. Many epidemiologists assume that the risk rises about the same regardless of how many grams of vegetables a person eats per day, for example. “The burden of proof allows us to better understand how risk actually changes with consumption,” the authors said.
In medicine, “there has always been some skepticism” about how changes in people’s behavior can affect their long-term health, especially when it comes to recommending specific foods or activities, said Christopher Murray, senior author of the papers and founder of IHME.
Clickbait titles and grocery cart contents reflect uncertainty. Cow’s milk is bad, and then it’s good. Fat—no, all fat—is supposed to go away, but then it comes back. Once the shopping cart is full, the Mediterranean, Keto, Paleo, and South Beach diets compete for magazine cover dominance in the checkout line. The peanut butter cups are looming. (Is chocolate good or bad? Wait, what about peanut butter?)
“Dietary research is really challenging,” said Jeffrey Stanaway, assistant professor of global health and lead author of the Vegetable Health Study Group analysis. It’s hard for researchers to measure how much people eat, do it over time, and separate their diet from other health factors (people who eat a lot of fruits and vegetables are more likely to exercise, for example).
Yet diet and other behaviors play an important role in disease prevention. About half of the US population has a chronic disease, and long-term diseases such as heart disease, diabetes and cancer are the main drivers of disability and death worldwide. “Most of what makes you healthy happens outside the doctor’s office,” said Georges Benjamin, executive director of the American Public Health Association.
By evaluating the available data on each link between eating vegetables and five different health outcomes, Stanaway was able to conclude: “The evidence for vegetables is pretty good,” he said. Even a conservative interpretation of the evidence which the IHME tool uses, have shown that eating more vegetables is associated with a reduced risk of chronic disease, although future studies may influence this. The model is intended to be updated and will be as additional research becomes available, the team said.
The three-star association between increased consumption of non-starchy, fibrous vegetables and ischemic stroke was the strongest association in the group. Data show that increasing vegetable consumption from one to four servings per day leads to about a 23% reduction in stroke risk. The analysis also showed a two-star rating for eating vegetables and heart disease (two on the edge of three, Stanway said). The study did not include starchy vegetables such as potatoes, sweet potatoes or corn, and also excluded dried and pickled vegetables (kimchi, sauerkraut).
For the most part, dietary habits score between one and three stars, indicating a need for more rigorous research. “I was very surprised how many of the diet-risk associations were much weaker” than expected, Murray said. He has a little more tolerance for eating red meat after seeing those results, he said.
everything evidence for red meat and its associations with disease are tenuous. This was not unexpected for Benjamin, who was not involved in the research. “Things that were always kind of unclear still seem kind of unclear,” he said.
The strongest ratings for a meat-rich diet were two stars — for colon and rectal cancer, breast cancer, coronary heart disease and type 2 diabetes. In the case of strokes, the researchers found that a diet high in red meat may actually have some protective effects and have given this evidence one star. Low star ratings should be seen as areas for research investment, the IHME team said — a large, well-designed study of people with high-red-meat diets could make a big impact.
Tobacco is often where all heated debate stops. There is a broad consensus among health professionals that tobacco smoking is harmful to humans. The IHME tool evidence found for strong or very strong associations between eight diseases or outcomes, including cancer of the larynx, aortic aneurysm, peripheral arterial disease of the lower extremities, cancer of the trachea, bronchi and lung, chronic obstructive pulmonary disease, and others.
“Tobacco is irrefutably a major health risk and indeed has a wide range of effects on multiple cardiovascular and cancer outcomes,” Murray said.
However, there was less solid evidence for the link between smoking and a host of other diseases, including coronary heart disease, esophageal cancer, stroke, type 2 diabetes, and others. Strangely, there is a star link between smoking and asthma, a finding that surprised the researchers. Cannabis smoking was not included in the analysis.
The risk of ischemic heart disease was closely related to high systolic blood pressure — a rating of five stars — confirming both common dogma among clinicians and the accuracy of the IHME tool, the researchers said at a news conference.
The IHME team has already analyzed nearly 200 other risk-outcome combinations, ranging from alcohol drinking, air pollution and high body mass index to other dietary factors, such as consumption of whole grains and legumes. Those results will be published in the future, Murray said.
Benjamin said it will take time for clinicians, policymakers and patients to see the value of this tool — data alone may not be enough to influence public understanding of risk.
Where the scoring system can be useful in the long term is in the doctor’s office, when the clinician is developing a care plan for a patient with multiple risk factors (say, smoking, high blood pressure, and low vegetable consumption). If what we know about these risks can be weighed against each other, then the doctor and the patient may have a better idea of what to prioritize, Benjamin said. “The fewer things you give people to do, the better and the more likely they are to comply,” he said.
STAT’s chronic health coverage is supported by a grant from Bloomberg Philanthropies. Ours financial supporters are not involved in any decisions about our journalism.
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