How does diet affect mortality risk?

• Unhealthy eating habits are among the leading causes of early death around the world.
• Harvard researchers have recently found that a variety of healthy diets may help lower the risk of premature mortality.
• In their extensive study, participants who consistently maintained healthy eating patterns were less likely to die from noncommunicable diseases, compared with people who did not.
• The results support the current Dietary Guidelines for Americans, which recommend adapting healthy dietary regimens according to personal traditions and preferences.

Growing evidence confirms that dietary choices are key to maintaining health. Research increasingly indicates that unhealthy eating habits can lead to early, preventable deaths.

Until now, though, studies have generally focused on the life-promoting benefits of individual foods or food components.

Researchers at the Harvard T.H. Chan School of Public Health in Boston, MA, recently led a study to see how long-term eating patterns affect mortality risks.

These experts assessed adherence to diets that align with the current Dietary Guidelines for Americans, 2020-2025 (DGAs). They then compared the results with other health data collected over 36 years from more than 100,000 people in two long-term national studies.

Corresponding author Dr. Frank Hu, Fredrick J. Stare professor of nutrition and epidemiology, and chair of the Department of Nutrition notes that “[t]he Dietary Guidelines for Americans are intended to provide science-based dietary advice that promotes good health and reduces major chronic diseases.”

“Thus, it is critical to examine the associations between DGAs-recommended dietary patterns and long-term health outcomes, especially mortality,” he adds.

The study findings appear in JAMA Internal Medicine.

The study methods

The Harvard researchers analyzed and combined results from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS).

The NHS, which began in 1976, tracked the health data of female nurses aged 30 to 55 years at baseline. The HPFS, which began in 1986, followed male health professionals aged 40-75.

Dr. Hu and his colleagues defined the baselines as 1984 for the NHS and 1986 for the HPFS, when questionnaires provided enough information to form dietary indices.

Their current work used data compiled from 75,230 NHS participants and 44,085 HPFS participants. All the individuals were free of cardiovascular disease or cancer when the study began.

At the baseline and every 2 to 4 years, the participants completed food frequency questionnaires (FFQs) covering over 130 food items every 2 to 4 years.

They also updated information regarding age, weight, body mass index (BMI), physical activity, smoking status, multivitamin use, menopausal status, and diagnosis of chronic diseases.

In the NHS, participants identified as Hispanic, non-Hispanic Black, non-Hispanic white, and “other.” The HPFS did not collect this information.

Comparing healthy diets

The researchers scored the data based on four dietary pattern indexes: Healthy Eating Index 2015 (HEI-2015), Alternate Mediterranean Diet (AMED), Healthful Plant-based Diet Index (HPDI), and Alternate Healthy Eating Index (AHEI).

All these diets share high consumption of vegetables, fruits, whole grains, nuts, and legumes. Some include animal-based foods while others eliminate them.

Higher scores on the indexes indicated greater compliance with the corresponding diet.

The study’s conclusions

Higher scores on at least one of the indexes also correlated with a reduced risk of premature death from all causes, and from cancer, cardiovascular disease, and respiratory diseases.

In the NHS and HPFS study populations, people with higher dietary scores were more likely to be older, nonsmokers, and more physically active. They also had a lower BMI.

Food choices and cancer

Kate Cohen, who was not involved in the present research, is a registered dietitian at the Ellison Clinic at St. John’s Health Center in Santa Monica, CA.

In an interview with Medical News Today, Cohen explained how diet can impact cancer development, saying: “We know that about half to two-thirds of cancers can be avoided through diet and lifestyle changes including staying at a healthy weight, increasing fruits and vegetables, limiting alcohol, and increasing dietary fiber.”

MNT also spoke about these findings with Dr. Monique Gary, a breast surgeon and the Medical Director of the Grand View Health/Penn Cancer Network cancer program. Dr. Gary was not involved in the study.

The oncologist shared that “[t]hese findings reinforce what we tell patients in oncology: that diet and lifestyle modification support all phases of cancer care and decrease [the] risk of recurrence and mortality.”

Diets and neurodegenerative diseases

The study also found that the AMED score and AHEI “were associated with lower risk of mortality from neurodegenerative disease.”

Cohen shared how these diets feature components that contribute to brain health:

“Both AMED and AHEI emphasize healthy fats more so than the other two patterns, which may provide an anti-inflammatory benefit and contribute to a healthy brain. They also both share some similarities to the MIND diet, which was developed at Rush Hospital to prevent dementia and slow down cognitive decline. Similar to MIND, AMED and AHEI limit red meat, sugar, and saturated fat, which may help tip the scales in favor of these diets when it comes to brain health.”

Smoking and sex-based differences

The Harvard scientists reported that “[s]ignificant interactions were detected between 4 dietary scores and total mortality by sex and smoking status.”

Female participants had a greater risk of death than male participants. Likewise, people who currently or had ever smoked had a greater risk of mortality than those who had never smoked.

Cohen believes that the sex-based difference might be due to “the potential role of estrogen and chronic pulmonary inflammation, which may be contributing to the dramatic rise of COPD and lung cancer among women.”

Benefit of eliminating meats?

The study results do not suggest that plant-based or animal-based diets offer greater health advantages. The HPDI discourages all animal products, while the AMED score recommends fish.

MNT asked Cohen whether removing meats from the diet is necessary.

She replied that “[w]e have seen in other research […] that diets highest in red and processed meat are associated with several cancers, so it’s likely a good idea to limit red meat and consider eliminating processed meats.”

However, she admitted, “[b]eyond that, we have yet to see a convincing study that shows that including lean animal proteins in the diet increases mortality.”

Strengths and limitations

The Harvard study entails a direct large-scale comparison of healthy dietary patterns over three decades. It steps beyond most current literature that focuses on single foods.

Dr. Gary pointed out that this analysis “highlights the fact that when normalized for race, and irrespective of the particular nuances of the healthy diet, adherence to a healthy diet may decrease mortality among all individuals with chronic illness.”

They did acknowledge certain limitations, though.

Due to dependence on self-reported data, the team felt that some measurement errors were unavoidable. Additionally, as an observational study, the possibility of confounding persists as well.

Moreover, the sample population consisted exclusively of health professionals, limiting the study’s generalizability.

Dr. Gary noted that “[f]urther studies will be helpful to better elucidate the benefits of particular dietary and lifestyle changes that result in a greater advantage for those facing chronic illnesses, including cancer.”

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