A new study finds that adopting a healthier lifestyle, including a diet rich in vegetables and fruits, can significantly reduce mortality risk. The study also revealed that people who maintain a healthy weight by eating less red meat and more vegetables and fruits have a lower mortality rate than those who opt for more “traditional” cuisines.
People who adopt healthier dietary patterns are more likely to engage in regular physical activity, which in turn reduces the risk of chronic diseases. While the study did not establish a direct cause-and-effect relationship, it did find evidence of a positive association between dietary changes and reduced mortality risk.
The research team from the Harvard T. H. Chan School of Public Health conducted a systematic review and meta-analysis of prospective cohort studies. The review included studies that examined the association between components of a healthy diet (vegetables, fruits, legumes, nuts, whole grains, and fish) and mortality risk. The study focused on studies that compared groups of people who had differing levels of adherence to healthy dietary patterns and were followed for at least five years.
This strategy allowed the researchers to identify 23 cohorts with 1,359,914 participants and an average follow-up period of 9.5 years. The cohorts came from 11 countries—Australia, Brazil, Denmark, France, Italy, Netherlands, New Zealand, Scotland, Spain, the United Kingdom, and the United States—and were of both sexes. The participants were 45 to 79 years of age at the time of enrollment. Study authors noted that many of the cohorts were initially established for the purpose of examining the effect of diet on health. Thus, they used data available from these cohorts to examine the association between diet and mortality risk.
The researchers found that higher adherence to a healthy diet was associated with an 18% reduction in all-cause mortality risk. When the analysis was restricted to studies that adjusted for body mass index (BMI), the team reported a 15% reduction in mortality risk. There was also a suggestion that higher adherence to a healthy diet was associated with a reduction in cardiovascular disease–specific and cancer–specific mortality.
The results of the study need to be interpreted in the context of several limitations, first and foremost the use of BMI as an indicator of body fatness. The researchers acknowledged that this indicator has several limitations, particularly when it comes to differentiating between fat and lean body mass. They noted that the variation in study results that they observed could be attributed to the use of different measures of body fatness. Another limitation is that the studies they analyzed included both overweight and obese participants. Thus, the results of the study cannot be generalized to the entire population, especially since non-adherence to a healthy diet has been shown to be associated with an increased risk of death. Still, this study provides important insights into the beneficial effects that a healthy diet can have on health and mortality risk.
The study also has several strengths, including the large number of participants and the long duration of the follow-up. Moreover, the researchers were able to combine data from multiple sources, including the Health Professionals Follow-up Study and the Nurses’ Health Study, to boost the statistical power of the analysis. This strategy allowed them to assess the effect of diet on mortality risk with greater precision.
Why Adopt a Healthy Diet?
One of the takeaways from this study is that adopting a healthy diet can confer significant health benefits. The research team hypothesized that the healthful qualities of a diet rich in vegetables and fruits, whole grains, nuts, and legumes might reduce the risk of death from cancer and heart disease. They suggested that these food groups could reduce chronic disease risk via several mechanisms of action, including reduced inflammation, enhanced antioxidant defenses, and changes in the gut microbiome. These mechanisms have been summarized in the “chemistry of health” graphic, which is included in this blog post. The diagram illustrates the possible mechanisms of action through which a diet rich in vegetables and fruits, whole grains, nuts, and legumes might reduce the risk of chronic disease. (Note: The graphic does not purport to be complete and is intended only to help readers who are interested in the topic navigate the large body of literature on dietary influences on health.)
To test their hypothesis, the study authors examined the association between diet and mortality risk in 23 cohorts from 11 countries. The cohorts were initially established for the purpose of examining the effect of diet on health and were followed for an average of 9.5 years. Diet was assessed using a validated 136-item food-frequency questionnaire or other similar tools, and all-cause and cause-specific mortality was ascertained using standard methods. Study authors conducted a systematic review and meta-analysis of the data and reported that higher adherence to a healthy diet was associated with a lower risk of mortality. Moreover, they noted that higher adherence to a healthy diet was associated with a reduced risk of cardiovascular disease–specific, cancer– specific, and all-cause mortality. The results of the study provide strong support for the hypothesis that a diet rich in vegetables and fruits, whole grains, nuts, and legumes can reduce mortality risk.
Because the study focused on prospective cohort data, it has the advantage of being able to assess the effect of diet on mortality risk with greater precision. Moreover, the results can be generalized to the population of interest (i.e., adults aged 45 to 79 years at the time of enrollment). However, the study did not establish a cause-and-effect relationship between diet and reduced mortality risk. Instead, it suggested that higher adherence to a healthy diet might be associated with a lower risk of death. As noted above, there are several study limitations—including the lack of a control group and the use of BMI as a measure of body fatness—that need to be considered when interpreting the results of this study. Nevertheless, the findings provide important insights into the benefits that a diet rich in vegetables and fruits, whole grains, nuts, and legumes can have on health and longevity.