ARTICLE IN BRIEF
Researchers identified specific elements of a diet — especially excess sodium intake and inadequate consumption of nuts and seeds — and how they are linked to specific causes of death for stroke, heart disease, and diabetes. They also calculated the fraction of preventable deaths due to suboptimal diet and other factors.
Nearly half of all deaths from heart disease, stroke, and diabetes — referred to as so-called cardiometabolic disease (CMD) — can be attributed to specific dietary factors — either too little or too much consumption of certain types of food, according to a March 7 report in the Journal of the American Medical Association.
The findings include a high proportion of stroke deaths related to poor diet, especially excess consumption of sodium and inadequate intake of seeds and nuts.
The results have important public policy implications, experts said, but also focus attention on the value of nutritional counselling of individual patients by neurologists and other physicians.
“We estimated that nearly half of all deaths from heart disease, stroke, and diabetes — collectively cardiometabolic diseases — are linked to poor diet,” the study's lead author Renata Micha, RD, PhD, research professor at the Tufts Friedman School of Nutrition Science and Policy, told Neurology Today. “Americans are overeating salt, processed meats, and sugary-sweetened beverages. This is especially true of men, younger adults, Blacks, and Hispanics, and people with lower levels of education.”
A large body of data has firmly established the association between diet and cardiometabolic disease, but the JAMA report breaks new ground in two important ways: It identifies specific elements of a diet — especially excess sodium intake and inadequate consumption of nuts and seeds — and how they are linked to specific causes of death; and calculates the fraction of preventable deaths due to suboptimal overall diet and its elements. The latter is important to policy makers, given that modification of diet is a cornerstone of prevention policy.
“We used separate evidence from pooled analyses of prospective studies and controlled trials on how diet impacts health, adjusted for other risk factors,” said the study's senior author Dariush Mozaffarian, MD, DrPH, dean of the Tufts Friedman School of Nutrition Science & Policy and the Jean Mayer Chair and professor of nutrition. “At the end of the day, our findings might modestly over- or under-estimate the health burdens, but several analyses suggested that this error is unlikely to be large. Even if our findings were substantially overestimated, whether poor diet is causing 1,000 cardiovascular and diabetes deaths per day, or 500, it remains among the leading causes of preventable suffering and health care spending.”
In the study, Dr. Micha and colleagues used a comparative risk assessment model to estimate the numbers and proportions of cardiometabolic deaths associated with suboptimal intakes of 10 dietary factors in the United States, both individually and in combination. The model incorporated data from four sources: population demographics and dietary habits by sex, age, race, and education from the National Health and Nutrition Examination Survey (NHANES); estimated relationships of 10 foods and nutrients with heart disease, stroke, or type 2 diabetes mortality, by age, from meta-analyses of prospective cohorts and randomized clinical trials; optimal population intake distributions of these dietary factors based on observed intakes associated with lowest risk in observational studies and general consistency with existing major guidelines; and observed US disease-specific cardiometabolic deaths by sex, age, race, and education from the National Center for Health Statistics (NCHS).
They estimated that 318,656 (45.4 percent) of CMD deaths in the United States in 2012 were linked to 10 dietary factors that they deemed to have “probable or convincing evidence” for causality with heart disease, stroke, diabetes, body mass index, or systolic blood pressure.
The highest proportion of CMD deaths related to excess sodium intake, accounting for 9.5 percent of CMD deaths. The other nine factors were low intake of nuts and seeds (accounting for 8.5 percent of CMD deaths), high intake of processed meats (8.2 percent), low seafood omega-3 fats (7.8 percent), low vegetables (7.6 percent), low fruits (7.5 percent), high sugar-sweetened beverages (7.4 percent), low whole grains (5.9 percent), low polyunsaturated fats (2.3 percent), and high unprocessed red meats (0.4 percent).
“The good news is that we now understand which foods we need to target to prevent Americans from dying prematurely from cardiometabolic diseases. These results are representative of all Americans and help us identify what's most important in the American diet.”
Of special importance to neurologists, Dr. Micha and colleagues found that that a total of 28,741 stroke deaths were attributable to suboptimal diet. “We did not evaluate the link between diet and other neurological conditions, such as Alzheimer's,” Dr. Micha said. “When it comes to preventing premature stroke deaths, eating more fruits, vegetables and whole grains, and eating less salt appear to be particularly beneficial.”
Nikolaos Scarmeas, MD, associate professor of clinical neurology at Columbia University and National and Kapodistrian University of Athens, told Neurology Today there has been a longstanding debate about which nutritional factors may be important for CMD and the relative importance of each factor.
“This has been proven quite challenging methodologically,” he said. “In this study, there is a very nice attempt to estimate effects for different dietary factors, to different CMD, exploring further differential associations in sociodemographic strata as well as changes of such associations over the course of a decade.
“It may be noteworthy for clinicians to know that policies for polyunsaturated fatty acids, nuts/seeds, and sugar-sweetened beverages seem to be working, while we are lagging behind in unprocessed red meat and sodium consumption related effects,” he said.
“For neurologists in particular, one could note the significant contribution of vegetables, fruits, and sodium in the stroke-related mortality. [For specifics, see the figure on page xx.] It is one more study underlying the important contribution of diet in all mortality but also in neurological mortality. It is an additional motivation to increase our counseling time with neurological patients on nutrition and lifestyle in general.”
Dr. Scarmeas said among the report's strengths is that it included the estimation of parameters from reliable sources, and the careful modeling of uncertainty. Weaknesses include the partial reliance of risk estimates for nutritional factors on observational studies, which may increase confounding and overestimate the nutrition-attributable risk in CMD, and the limitations of estimation of possible interactions among the selected factors (or among other dietary factors that could have been included in such analyses).
Andrew Smyth, MD, a research fellow at the Population Health Research Institute of McMaster University and Hamilton Health Sciences, said the findings of the report have implications for both public policy and individual patient health.
“This paper provides important data regarding the association between diet and cardiometabolic disease by including a broad range of nutrients. Differences in the observed associations between gender, race, education and cardiometabolic disease provide important data on the importance of diet quality for future health policy,” he said. “This is consistent with other studies highlighting the importance of overall diet quality in disease prevention.
“The paper reinforces the importance of counselling patients on adhering to dietary guidelines and improving the quality of diet for the prevention of cardiometabolic disease,” Dr. Smyth told Neurology Today. “This message is important for all clinicians, although perhaps more important for primary care physicians to facilitate primary prevention.”
In an editorial that accompanied the report, Noel T. Mueller, PhD, MPH, and Lawrence J. Appel, MD, MPH, also added a cautionary note. “The precision of the estimates reported by Micha, et al, should be interpreted cautiously given that the excess fraction of CMD deaths related to suboptimal diet relies on the strong assumption of causality, the number of factors included and accurate estimation of their effect size, and the extent to which each of the factors interact with each other on risk of CMD,” they wrote.
“Whether the authors overestimated or under-estimated the potential effects of improved diet, the likely benefits are substantial and justify policies designed to improve diet quality,” they concluded.
Dr. Micha suggested the take-home message for clinicians should be an encouraging one. “Positive messaging to patients can emphasize maximizing the good, rather than simply reducing the bad food choices and products, and on foods versus simply on nutrients,” she said.
“Eat more fruits, vegetables, nuts/seeds, whole grains, vegetable oils and fish. And eat less salt, processed meats, and sugary-sweetened beverages. Start by making one healthier choice each day and build on it.”
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