In a recent study published in JAMA Network Open, researchers evaluate the impact of planetary health diet (PHD) adherence on environmental and human health.

Study: Adherence to a Planetary Health Diet, Environmental Impacts, and Mortality in Chinese Adults. Image Credit: Created with the assistance of DALL·E 3

Background

PHD is characterized by an increased consumption of plant-based foods and reduced intake of animal food products. The influence of PHD on environmental and mortality outcomes among Asians is unknown.

Previous studies have proposed grading techniques to quantify PHD adherence; however, no agreement has been reached. Furthermore, these trials were exclusively performed among Western individuals without considering individual-level calorie consumption and varied levels of PHD adherence.

To date, few studies have evaluated the link between PHD, environmental variables, and mortality using individual-level data.

About the study

In the present study, researchers investigate whether PHD scores were related to environmental effects and fatalities among Chinese Singaporeans. To this end, a grading system was devised to evaluate PHD adherence and study the associated advantages to environmental and human health.

The researchers examined the Singapore Chinese Health Study (SCHS) participants' data. Individuals without a history of cardiovascular disease or cancer and permanent residents of Singapore speaking Cantonese or Hokkien dialects were enlisted from 1993 to 1998 and followed up on utilizing record linkage data until 2020. Data were analyzed between September 2022 and April 2023.

PHD scores were determined using standardized food frequency questionnaires recording the consumption of 14 dietary elements in PHD and individual calorie intake. These surveys were also used to quantify the environmental implications of the diet. Death outcomes, including all-cause mortality, respiratory disease, cardiovascular disease, and cancer, were ascertained using national registry data.

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The total water footprint (TWF), land utilization, and greenhouse gas (GHG) release were estimated using the China Health and Nutrition Survey database. These data were used to determine dietary impacts on the environment based on the mean effects determined by dividing the environmental effects by each gram of a food item consumed by the quantity consumed. The amount of GHG emitted was calculated from the period between food production and consumption.

TWF was calculated using the WF Network database for non-aquatic foods, whereas for aquatic food items, TWF was determined using a prior study's technique. The Food and Agriculture Organization (FAO) database was used to estimate land utilization.

Professional interviewers performed offline interviews utilizing standardized questions to obtain data. The International Classification of Diseases, Ninth and Tenth Revisions (ICD-9 and 10) codes were used to categorize deaths.

Linear regression modeling was performed to determine the relationships between PHD scores and environmental effects, adjusting for age, gender, body mass index (BMI), educational attainment, physical activity, smoking status, alcohol intake, sleep duration, total calorie intake, diabetes, and hypertension. Cox proportional regression modeling was performed to determine the hazard ratio (HR) values for the relationships between PHD scores and mortality risks.

Sensitivity analyses were conducted by excluding participants with diabetes or hypertension, as well as those who died within five years after enrollment, and utilizing PHD-S computed using various methodologies. The researchers eliminated 1,060 individuals with an implausible calorie intake of less than 600 or over 3,000 kcal per day for women and less than 700 or over 3,700 kcal per day for males.

Study findings

A total of 57,078 individuals were included in the study, with a mean age of 56 years, 56% of whom were female. During a median follow-up of 23 years, 22,599 deaths were reported.

The median PHD score was 55 points and ranged from 13 to 95 points. PHD adherence was low among the participants, with over 80% reporting good compliance with unsaturated fats, fish, and fruits.

The median values of land utilization, TWF, and GHG releases from daily dietary intake were 3.1 m², 2.5 m³, and 2.7 kg carbon dioxide (CO₂) equivalents, respectively. Higher PHD scores reduced GHG emissions by 7% but elevated land usage by 10% and TWF by 8%.

Individuals in the topmost quintile of the PHD score had a decreased risk of all-cause fatalities, cardiovascular disease mortality, cancer mortality, and respiratory disease mortality compared to the lowermost quintile. Individuals with higher PHD adherence were more likely to be younger at an average of 54 years as compared to 57 years, female, more educated, non-smokers, non-alcoholic consumers, and physically fit.

Total grains, fish, and red meat contributed the most to GHG emissions at 55%, 11%, and 9%, respectively. Grains primarily contributed to land utilization at 34% and TWF at 37%. The corresponding contributions by fruits were 10% and 8.6%, respectively.

Red meat, dairy, chicken, and fish contributed 11%, 10%, 8.4%, and 5.9% of land use, respectively. Sensitivity analyses produced comparable results, thus indicating the robustness of the primary findings.  

Conclusions

Increased PHD adherence was attributed to a reduced risk of death from chronic diseases. However, environmental impacts were unknown, as improved abidance to PHD was associated with reduced GHG emissions but greater land utilization and water footprints.

Journal reference:

• Ye, Y., Geng, T., Zhou, Y., et al. (2023). Adherence to a Planetary Health Diet, Environmental Impacts, and Mortality in Chinese Adults. JAMA Network Open 6(10):e2339468. doi:10.1001/jamanetworkopen.2023.39468, https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2810988