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Are Plant-Based Diets Necessarily More Sustainable?

There has been significant debate and dialogue about sustainable diets.

A number of studies indicate that increasing the consumption of fruits and vegetables, while decreasing the consumption of animal-based foods, may be better for the environment.1,2 But the picture isn’t that clear.

There is evidence to suggest that diets high in fruits and vegetables and low in meat may not necessarily have a lower environmental impact. This is due to the fact that a higher amount of plant-based substitutes needs to be consumed to replace animal proteins and calories.1,3 In fact, one study showed that when meat and deli meat were isocalorically replaced by fruits and vegetables there was either no effect or an increase in greenhouse gas emissions (GHGE).4

Other elements to consider with plant-based diets1,4,5

  • Most studies indicate that animal-based foods generate more GHGE than plant-based foods. However, fruits and vegetables grown in greenhouses actually generate more GHGE than animal-based foods.
  • While vegetables and grains need higher-quality land to grow, lower-quality land is generally used for forage crops, which are not consumed by people.
  • A strict plant-based diet would require a significant shift in eating habits and could lead to nutritional deficiencies.
  • Sustainable and certified produce tends to be more expensive, which is a barrier to accessing a healthy, sustainable diet.

Studies from different countries

  • A modelling study conducted in the UK suggests that a healthy diet following national nutrition guidelines could lead to lower GHGE without eliminating meat or dairy products and without increasing the cost to the consumer.6
  • Another modelling study from Australia showed that nutrient-poor foods (such as cakes, biscuits, chips, desserts, soft drinks and processed meats) accounted for 27% of diet-related GHGE.7
  • In a prospective cohort study of 40,011 subjects in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Netherlands cohort, researchers found that GHGE and land use related to a usual diet were not associated with all-cause or cause-specific mortality.8
  • A French national dietary survey of 1,918 adults found that:9  
    • GHGE for dairy, mixed dishes, pork, poultry, eggs and fish were 2 to 5 times higher than for fruits and vegetables, when calculations were done based on food weight (i.e., per 100 g);
    • But when the focus was energy density (i.e., per 100 kcal), GHGE for fruits and vegetables were 25% higher than for dairy products and similar to those calculated for mixed dishes, pork, poultry and eggs.

Conclusion

The research shows that a message which simply suggests switching to a strict plant-based diet may not lead to better environmental outcomes.

More research is needed to better understand what dietary changes are needed to achieve sustainable, healthy diets that are realistic and acceptable.


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