A Sustainable Diet for Our Planet

An October 2018 study 1 entitled “Health and nutritional aspects of sustainable diet strategies and their association with environmental impacts: a global modelling analysis with country-level detail” has just been published in the Lancet. Will the findings show that there is any health/environmental benefit if populations around the world transitioned from an animal-based to a plant-based diet? Let’s find out…

Study background

There are considerable concerns about the negative impact that current trends in food production and consumption are having on human health and the environment we live in – including, of course, all the other species that share this planet with us. Thus, there’s increasing pressure to find sustainable diets that can address these issues.

This study looks at more than 150 countries, and examines the following four different diets:

  • flexitarian
    • no processed meat, small amounts of red meat (one serving per week), moderate amounts of other animal-source foods (poultry, fish, and dairy), and generous amounts of plant-based foods (fruits, vegetables, legumes, and nuts)
  • pescatarian
    • meat replaced with two-thirds fish and seafood and a third fruits and vegetables
  • vegetarian
    • meat replaced with two-thirds legumes and a third fruits and vegetables
  • vegan
    • all animal-source foods replaced with two-thirds legumes and a third fruits and vegetables

Study methods

To produce the wide-reaching global model they required, the researchers combined analyses of:

  • nutrient levels
  • diet-related chronic disease mortality
  • weight-related chronic disease mortality
  • general environmental impacts

They focused on three major objectives:

  • environmental
    • replacing 25-100% of animal-source foods with plant-based foods
  • food security
    • reducing levels of underweight, overweight, and obesity by 25-100%
  • public health
    • analysing the above-mentioned four dietary patterns (flexitarian, pescatarian, vegetarian, and vegan)

Their analyses took into account:

  • required nutrient content and sufficiency of supply
  • changes in mortality based on predicted changes in diet- and weight-related risk
  • country-specific and food group-specific footprints for:
    • greenhouse gas emissions
    • cropland use
    • freshwater use
    • nitrogen application
    • phosphorus application

These would help to analyse the relationship between the health and environmental impacts of any given dietary change.

Study findings

Replacing animal-sourced foods with plant-based ones was predicted to result in the following:

  • there would be an improvement in nutrient levels, particularly in high-income countries
  • premature mortality would be greatly reduced (more for a vegan than for a flexitarian diet)
  • a range of environmental impacts would reduce
    • for instance, greenhouse gas emissions could be reduced by up to 84%
  • freshwater use would:
    • increase by up to 16% if everyone ate a completely meat-free diet
    • reduce by 2-11% if meat-consumption was reduced greatly where it was energy-efficient to do so
  • nitrogen application could reduce by 23-25%
  • phosphorus application could reduce by 18-21%
  • cropland use could reduce by 8-11%
  • freshwater use could reduce by 2-11%

Study conclusion

A public health strategy focused on improving energy balance and dietary changes towards predominantly plant-based diets that are in line with evidence on healthy eating is a suitable approach for sustainable diets.

Final thoughts

Whilst this extensive study came up with the sort of conclusion most of us would expect, there are a few anomalies.

Firstly, the researchers consider that a meat-reduced diet would reduce greenhouse gases slightly more than a completely meat-free diet. I think this might in part be due to an increased need for transportation of plant-foods to areas where growing plants was not possible.

Secondly, the increased use of freshwater for completely meat-free diets, compared with largely meat-free diets where it is energy-efficient to do so, might be because eating fish and crustacea, where they are easily available, is more efficient than planting crops or having crops transported to the population concerned. This may also apply to areas where hunting wild animals, rather than planting crops, would have some energy-saving benefit.

Thirdly, in this study, there appears to be little recognition of the many negative effects of a meat-based diet on human health (and, of course, on the health of other species, not least the animals that act as our food). The harms to human health that animal foods produce, and which plant foods do not, is not mentioned in this study.

The authors’ final words are: “Finding effective combinations of policies and approaches that consider local characteristics will be essential for successfully upscaling initiatives and achieving reductions in the health and environmental burden at the population level and globally.

This may be taking into account those places where it is either impossible or impractical to grow crops 2 compared with either eating sea food, hunting wild animals or keeping some form of livestock that can exist on land that humans could not cultivate. This may account for the above findings related to the greater freshwater usage and slightly lower reductions in greenhouse gases if everyone adopted a completely meat-free diet.


References

  1. Lancet Planet Health. 2018 Oct;2(10):e451-e461. doi: 10.1016/S2542-5196(18)30206-7.
    Health and nutritional aspects of sustainable diet strategies and their association with environmental impacts: a global modelling analysis with country-level detail. Springmann M, Wiebe K, Mason-D’Croz D, Sulser TB, Rayner M, Scarborough P. []
  2. The main physical factors that make agriculture possible or impossible are: Climate. Some crops grow better in one climatic zone than in others. In general, plants cannot grow in areas with very high temperatures (above 45°C) or very low ones (below 10°C). They cannot grow in areas with too little rain or too much rain. Landscape. Relief (altitude and the gradient of terrain) influences agricultural activity. At higher altitudes, temperatures descend, and this limits species development. Gradients of terrain above 10° make it impossible to cultivate the land. Consequently, agriculture usually takes place on plains or in valleys. However, where it is necessary, hard work can transform mountain sides into cultivated terraces. Soil. Plants need soil with certain characteristics. The grain size and porosity of the soil affect the amount of oxygen the soil contains, and its ability to retain water. The chemical and biological composition of soil determines its degree of acidity, the quantity of mineral nutrients, and available organic matter. []