PHD linked to longer life in Asians, but environmental effects unclear

Adherence to a planetary health diet (PHD) is beneficial to health, lowering the risk of mortality among Chinese adults in Singapore, according to a study. But the benefits to the environment are less certain.

PHD is touted as the optimal diet for the people and the planet. Proposed by the EAT-Lancet commission in 2019, the diet encourages people to eat plant-based foods but allows the flexibility of optionally consuming modest amounts of fish, meat, and dairy products. This is said to promote environmental sustainability. [Lancet 2019;393:447-492]

Data from the Singapore Chinese Health Study showed that compared with the lowest quintile of PHD score (13–47; lowest adherence), the highest quintile (63–95; highest adherence) was associated with decreased risk of all-cause mortality (hazard ratio [HR], 0.85, 95 percent confidence interval [CI], 0.81–0.89; p<0.001), as well as risks of death from cardiovascular disease (CVD; HR, 0.79, 95 percent CI, 0.73–0.85; p<0.001), cancer (HR, 0.93, 95 percent CI, 0.86–1.00; p=0.04), and respiratory disease (HR, 0.81, 95 percent CI, 0.74–0.89; p<0.001). [JAMA Netw Open 2023;6:e2339468]

The risk-reduction benefit was also seen for subtypes of mortality from CVD and respiratory disease, such that participants in the highest quintile were 11–35-percent less likely to die of ischaemic heart disease, stroke, pneumonia, and chronic obstructive pulmonary disease (COPD).

“Furthermore, we observed that the inverse association of PHD with mortality was stronger among individuals who had ever smoked than those who had never smoked, which may be explained by antioxidant nutrients in vegetables and fruits in PHD providing greater benefit for smokers than for never-smokers,” the investigators noted. [Eur J Nutr 2022;61:2375-2382]

The finding that PHD helps promote longevity is consistent with data from previous studies, including the EAT-Lancet report, the Malmö Diet and Cancer cohort study, and EPIC study. [Lancet 2019;393:447-492; Lancet Planet Health 2018;2:e451-e461; Am J Clin Nutr 2022;115:705-716; Lancet Planet Health 2021;5:e786-e796]

But unlike the others, the Singapore Chinese Health Study “is the first to find an inverse association between adherence to PHD and the risk of respiratory disease mortality, especially mortality from COPD,” the investigators said.

“Although the risk estimates in the fully adjusted model 2, which included strong risk factors for COPD such as smoking and body mass index, were substantially attenuated compared with those in the minimally adjusted model 1, the risk estimates were still statistically significant. This suggests that even after accounting for smoking and body mass index, improving diet quality could still have beneficial health effects for respiratory disease mortality,” they added.

Increased water, land use

When it comes to the environment, however, the present study showed that PHD adherence may have less favourable consequences. Higher PHD scores were associated with lower greenhouse gas emissions (β, –0.13 kg CO2 equivalent) and higher total water footprint (β, 0.12 m3) and land use (β, 0.29 m2).

Increased total water footprint and land use were driven by greater consumption of grains (37.25 percent of total water footprint and 34.39 percent of land use) and fruits (8.61 percent and 10.28 percent, respectively).

“Red meat was also resource-intensive and was responsible for 10.07 percent of total water footprint and 10.86 percent of land use. Aside from red meat, animal-based food with the highest land use included dairy (10.35 percent), poultry (8.38 percent), and fish (5.87 percent),” the investigators pointed out.

They noted that while higher intakes of fruits, dairy, vegetables, and legumes raised the PHD score, total water footprint and land use also increased. In contrast, reduced consumption of red meat and total grains raised the raised the PHD score and contributed to lower total water footprint and land use at the same time.

“As such, we recommend a reduction in the intake of total grains and red meat to offset the environmental impacts on total water footprint and land use from increased consumption of the recommended dietary components,” the investigators said.

“More studies should be conducted in other populations to determine the cobenefit for human and environmental health so as to establish unequivocal evidence that supports a worldwide implementation of PHD,” they added.

A total of 57,078 participants were included in the analysis (median age 55.0 years, 56.0 percent women). Younger participants, women, never smokers and nondrinkers, among others, tended to have higher adherence to PHD. Overall, the population consumed more fruits, fish, grains (mostly refined), red meat, and saturated fats and less vegetables, nuts, legumes, unsaturated fats, sugar, potatoes, dairy, and poultry than what was recommended by the PHD. The PHD score ranged between 13 and 95 points, with a median of 55 points, which indicated low adherence.

Over a median follow-up of 23.4 years, 22,599 cases (39.6 percent) of deaths were recorded, including 6,948 CVD deaths, 7,338 cancer deaths, and 4,891 respiratory disease deaths.