Can an earth-healthy diet save your life and the planet?Study finds mixed results

In a recently published study JAMA Network Openresearchers evaluated the impact of adherence to a Planetary Health Diet (PHD) on the environment and human health.

study: Adherence to a planet-healthy diet, environmental impacts, and mortality among Chinese adults.Image source: Created with the assistance of DALL·E 3

background

PHD is characterized by increased intake of plant foods and decreased intake of animal foods. The impact of PHD on environmental and mortality outcomes in Asians is unknown.

Previous studies have proposed scoring techniques to quantify PHD compliance; however, no agreement has been reached. Furthermore, these trials were conducted exclusively among Westerners and did not take into account individual-level caloric consumption and varying levels of PHD compliance.

To date, few studies have used individual data to assess the association between PHD, environmental variables, and mortality.

About the study

In this study, researchers investigated whether PHD scores were associated with environmental impact and mortality among Chinese Singaporeans. To this end, a grading system was designed to assess PHD compliance and study the associated benefits to the environment and human health.

Researchers examined data from participants in the Singapore Chinese Health Study (SCHS). Individuals with no history of cardiovascular disease or cancer and Cantonese- or Hokkien-speaking Singapore permanent residents were recruited between 1993 and 1998 and followed up until 2020 using record-linked data. Data was analyzed between September 2022 and April 2023.

PHD scores were determined using a standardized food frequency questionnaire recording consumption of 14 dietary elements and individual caloric intake in PHD. These surveys are also used to quantify the environmental impact of diet. Mortality outcomes, including all-cause mortality, respiratory disease, cardiovascular disease, and cancer, were determined using national registry data.

Total water footprint (TWF), land use, and greenhouse gas (GHG) emissions were estimated using the China Health and Nutrition Survey database. These data are used to determine the environmental impact of a diet based on average impact, which is determined by dividing the environmental impact by the amount consumed per gram of food. Greenhouse gas emissions are calculated based on the period of food production and consumption.

The TWF of non-aquatic foods was calculated using the WF Network database, while the TWF of aquatic foods was determined using previously studied techniques. The Food and Agriculture Organization (FAO) database was used to estimate land use efficiency.

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

Linear regression models were performed to determine the relationship between PHD scores and environmental influences, adjusting for age, sex, body mass index (BMI), education, physical activity, smoking status, alcohol intake, sleep duration, total calorie intake, diabetes, and hypertension. Cox proportional regression models were performed to determine hazard ratio (HR) values ​​for the relationship between PHD score and mortality risk.

Sensitivity analyzes were performed by excluding participants with diabetes or hypertension and those who died within five years of enrollment and using PHD-S calculated using various methods. The researchers excluded 1,060 individuals who consumed less than 600 or more than 3,000 kcal per day for women and less than 700 or more than 3,700 kcal for men.

Research result

A total of 57,078 people participated in the study, with an average age of 56 years, 56% of whom were women. During a median follow-up of 23 years, 22,599 deaths were reported.

The median PHD score was 55 points, with a range of 13 to 95 points. Participants’ PHD compliance was low, with more than 80% reporting good compliance with unsaturated fats, fish and fruits.

Median land use, TWF and GHG emissions from daily dietary intake are 3.1 m22.5 m3and 2.7 kilograms of carbon dioxide (CO2) are equivalent respectively. Higher PHD scores reduce GHG emissions by 7%, but increase land use by 10% and TWF by 8%.

Individuals in the highest quintile of PHD scores had a lower risk of all-cause mortality, cardiovascular disease mortality, cancer mortality, and respiratory disease mortality than those in the lowest quintile. Individuals with higher PHD compliance were more likely to be younger, with an average age of 54 years compared to an average of 57 years, to be female, to be more educated, to be non-smokers, non-alcoholics, and to be in good health.

Cereals, fish and total red meat contribute the most to greenhouse gas emissions, at 55%, 11% and 9% respectively. The contribution rate of grain to land use is mainly 34%, and TWF is 37%. The corresponding contributions of fruits are 10% and 8.6% respectively.

Red meat, dairy products, chicken and fish account for 11%, 10%, 8.4% and 5.9% of land use respectively. Sensitivity analyzes yielded comparable results, thereby demonstrating the robustness of the main findings.

in conclusion

Increased PHD compliance has been attributed to reduced risk of mortality from chronic diseases. However, the environmental impact is unclear, as increased compliance with PHD is associated with reduced greenhouse gas emissions but increased land use and water footprint.

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