Wednesday, 27 Sep 2023

Heart-Protective Diet in PURE Study Allows Whole-Fat Dairy

Diets containing higher amounts of certain food categories appear to be protective against cardiovascular (CV) disease and premature death, suggests a new study with a broad international scope. Most of the protective food categories are in line with standard dietary guidelines for good health, but one that may be heart-protective is not usually included in such recommendations.

The food categories that were found to be protective include fruit, vegetables, nuts, legumes, and fish but also dairy, “mainly whole-fat,” in an analysis based on the international Prospective Urban and Rural Epidemiological (PURE) study and data from five other international trials that encompassed more than 240,000 people.

A healthy diet scoring system was derived from dietary patterns and clinical events observed in the PURE study and was applied to the populations of the other trials. Higher scores, corresponding to greater consumption of the six food categories, tracked with significantly reduced risks for death, myocardial infarction (MI), and stroke.

Reductions in mortality and CV-disease risk that were linked to the higher scores were especially pronounced in lower-income countries in the study published online July 6 in the European Heart Journal with lead author Andrew Mente, PhD, Population Health Research Institute, McMaster University, Hamilton, Ontario, Canada.

The study in part refutes the frequent preference for low-fat or no-fat dairy foods over whole-fat dairy in healthy-diet recommendations. But it is consistent with earlier findings from PURE of reduced mortality risk with increased consumption of dietary fat, including saturated fat.

Whereas healthy-diet recommendations tend to emphasize reduced intake of fat, especially saturated fat, the report notes that “there are almost no national or international strategies and policies to increase a number of protective foods,” such as nuts, fish, and dairy.

“Therefore, while the findings from PURE are largely consistent with the nutrition science and modern dietary recommendations to focus on protective foods, the public’s understanding of healthy eating and relevant global policies have not yet caught up to this science,” it states.

“Guidelines and policy actions need to be updated with this newer evidence,” Mente told Cardiology. “For example, the World Health Organization remains mainly focused on reducing certain nutrients, such as fat, saturated fat, added sugar, and salt,” he said. “These recommendations are echoed by government policy actions and industry, as evident by the continued focus on the usual nutrients in food labels of many countries.”

The current findings, Mente said, “can be used to ensure that the public’s understanding of healthy eating and relevant global policies are able to catch up to the science.”

Healthy Diet Score

PURE investigators developed their healthy diet score using data from 147,642 people from the general population in 21 countries. The investigators compared self-reported dietary intakes with long-term clinical outcomes.

The scoring system assigned a value of 1 for each of the six health-food categories when individuals’ intake exceeded the entire cohort’s median intake. It assigned a 0 when intake was below the median. The total PURE healthy diet score consisted of the sum of the six values, with higher scores corresponding to a healthier diet. The mean score for cohort was 2.95.

There were 15,707 deaths and 40,764 CV events during a median follow-up of 9.3 years. A score of at least 5 points, compared with 0 or 1 point, was associated with significantly reduced hazard ratios (HRs) for mortality, MI, and stroke in multivariable analysis:

  • Mortality: HR, 0.70 (95% CI, 0.63 – 0.77; P < .0001)

  • Major CV disease: HR, 0.82 (95% CI, 0.75 – 0.91; P < .0001)

  • MI: HR, 0.86 (95% CI, 0.75 – 0.99; P = .0014)

  • Stroke: HR, 0.81 (95% CI, 0.71 – 0.93; P = .0034)

The healthy diet score’s relationship to clinical outcomes was explored in five other large independent studies, including three prospective trials of patients with CV disease that spanned 50 countries, a case-control study with MI patients in 52 countries, and a case-control study with stroke patients in 33 countries.

In the three prospective trials, higher scores were associated with reduced mortality, CV disease events, and MI:

  • Mortality: HR, 0.73 (95% CI, 0.66 – 0.81)

  • Major CV disease: HR, 0.79 (95% CI, 0.72 – 0.87)

  • MI: HR, 0.85 (95% CI, 0.71 – 0.99)

In the two case-control studies, a higher diet score was associated with reduced odds ratios (ORs) for first MI and for stroke:

  • MI: OR, 0.72 (95% CI, 0.65 – 0.80)

  • Stroke: OR, 0.57 (95% CI, 0.50 – 0.65)

In an analysis based on the PURE cohort, incorporation of unprocessed red meat or whole grains into the health diet score produced similar results, suggesting that a “modest amount” of meat or whole grains can be part of a healthy diet, the authors contend.

The results were similar in a combined analysis of all the prospective studies. In particular, improvement in diet score by one quintile was associated with significantly reduced risks for the following:

  • Mortality: HR, 0.92 (95% CI, 0.90 – 0.93)

  • Major CV disease: HR, 0.94 (95% CI, 0.93 – 0.95)

  • MI: HR, 0.94 (95% CI, 0.92 – 0.96)

  • Stroke: HR, 0.94 (95% CI, 0.89 – 0.99)

  • Death or CV disease: HR, 0.93 (95% CI, 0.92 – 0.94)

“This strongly indicates that the take-home message for patients is the same as for general populations,” Mente said. “Eat plenty of fruits, vegetables, nuts, legumes, and a moderate amount of fish and whole-fat dairy to lower risk of CV disease and mortality.”

Dairy foods are not widely consumed in some cultures, he said, “but availability and cost are also factors in determining consumption.” Nonetheless, a high-quality diet can be achieved without including or excluding dairy foods. Context-specific policies and priorities are needed for different populations, “rather than a one-size-fits-all global policy.”

Food labels in many countries mainly focus on “reducing certain nutrients as the end-all, be-all,” Mente observed. “Our findings can be used as a basis for recommendations regarding what a healthy diet should be globally and then modified for each region based on the specific types of foods that are available and affordable in each region.”

Moreover, he said, “targeted food policies are needed to increase the availability and affordability of healthy foods, especially in lower-income countries where intakes are low.”

Common Human Biology

The current results from PURE “confirm prior observations from mostly Western nations that low intakes of fruits, vegetables, nuts, legumes, and fish are major risk factors for poor health,” observes Dariush Mozaffarian, MD, DrPH, MPH, Friedman School of Nutrition Science and Policy, Tufts University, Boston, in an accompanying editorial. “This suggests that common human biology, not merely confounding, explains these observed diet–disease relationships, strengthening causal inference on the power of nutrition.”

Moreover, “These findings provide further support that dairy foods, including whole-fat dairy, can be part of a healthy diet,” Mozaffarian writes. “The new results in PURE, in combination with prior reports, call for a re-evaluation of unrelenting guidelines to avoid whole-fat dairy products.”

Such studies “remind us of the continuing and devastating rise in diet-related chronic diseases globally, and of the power of protective foods to help address these burdens,” the editorial continues. “It is time for national nutrition guidelines, private sector innovations, government tax policy and agricultural incentives, food procurement policies, labelling and other regulatory priorities, and food-based healthcare interventions to catch up to the science.”

Not Automatically Superior

“I do not believe guidelines should be changed based on this single study,” contends Howard D. Sesso, ScD, MPH, associate director of the Division of Preventive Medicine at Brigham and Women’s Hospital, Boston, who isn’t part of PURE. “But I welcome the scientific dialog that should come out of any study that challenges what we think we know,” he told / Medscape Cardiology.

“Many other dietary patterns have been identified over the years that also do a great job in predicting disease risk in observational studies,” observed Sesso. “Is PURE that much better? Maybe, maybe not. But not enough to dismiss other dietary patterns that are already the basis of dietary recommendations in the US, Europe, and worldwide.”

The PURE healthy diet score, he said, “appears to work well within the confines of their large pooling of studies around the world, but that doesn’t automatically make it superior to other dietary patterns.” The score “was only modestly, but not greatly, better than existing dietary patterns evaluated.”

Randomized controlled trials are needed, Sesso said, to “delve into more specific dietary components,” including unprocessed red meat, whole grains, and high-fat dairy foods. And, he said, more observational studies are needed to examine the score’s association with other cardiometabolic outcomes.

The PURE study is funded by the Population Health Research Institute, the Hamilton Health Sciences Research Institute, the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Ontario; with support from Canadian Institutes of Health Research’s Strategy for Patient Oriented Research through the Ontario SPOR Support Unit, as well as the Ontario Ministry of Health and Long-Term Care; and through unrestricted grants from several pharmaceutical companies, with major contributions from AstraZeneca, Sanofi-Aventis, Boehringer Ingelheim, Servier, and GlaxoSmithKline. Additional contributions are from Novartis and King Pharma. Mente, Mozaffarian, and Sesso have disclosed no relevant financial relationships.

Eur Heart J. Published online July 6, 2023. Full text, Editorial

Follow Marilynn Larkin on Twitter: @MarilynnL.

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