We all want to do more to save our planet but we still don’t know for sure how best to achieve this. Now a study has shown that we can make a big difference simply by eating a healthy diet with lots of fruit and vegetables.
In the study, the authors found that we could cut greenhouse gases associated with our diet by nearly a third, without having to make major changes to the foods we eat. We just need to choose more plant-based foods than many of us do currently, and cut back on meat (to about 100 g/day). And the good news is, it won’t add to our shopping bill.
The not-so-good news is that the amount we can cut greenhouse gases is limited by the need for our diet to provide us with enough healthy nutrients. So achieving bigger falls in greenhouse gases would come at the cost of a healthy diet, or require us to make much bigger changes to our diets – a sacrifice that many people aren’t yet ready for, say the authors.
Food production creates greenhouse gases
The foods we eat can have an impact on the environment through the ways they are grown, processed, transported, stored and even thrown away. Reducing emissions arising from this food system could be partly achieved if we all made a shift in our normal diet. That’s because the same quantities of different foods generate different levels of greenhouse gas. Meat, for example, generates more greenhouse gas emissions (GHGEs) than fruit and vegetables. A vegetarian diet or one that’s low in meat products can be seen as having a lower environmental impact, and generally this matches health experts’ advice to eat lots of plant-based foods and less red or processed meat.
However, cutting GHGEs must be balanced against the other components that make up a sustainable diet: it should contain enough nutrients, be safe and healthy, affordable, and culturally acceptable as well as having a low impact on the environment.
Modelling diets to mimic the effects of dietary changes
The authors therefore looked at what the effects would be of varying these components of the sustainable diet. They assessed the nutrient content, prices, and GHGEs associated with 402 foods among those most eaten by participant in a large French study. They then used a mathematical technique to model diets based on changes in GHGEs, nutritional quality, and acceptability.
Their GHGE calculations included the whole life cycle of foods, from farm production to use and waste management of packaging.
‘… the present study reveals that moderate GHGE reductions did not require any dietary shifts at the food group level additional to those induced by meeting nutritional recommendations, i.e. mainly an increase in fruits and vegetables.’ – Perignon M et al, 2018.
Results showed that participants could reduce GHGE by up to 30% without having to spend more or having to make changes in food groups other than those needed to meet nutritional recommendations.
Beyond this, cutting GHGE by more than 30% couldn’t be achieved without impairing diet quality or requiring drastic changes to participants’ usual food choices.
The greatest reduction that could be achieved in GHGE while meeting all nutritional recommendations was about 70%. But these greatest reductions could only be reached through cutting out some food groups, such as dairy, meat and eggs.
Should we all become vegetarian?
So, the study showed that animal-based foods are the main levers to reduce diet-related GHGE. But expecting everyone to become vegetarian might be a step too far, say the authors. Such a sweeping change in people’s diets may not be realistic in industrialised countries such as France and the USA, where only about 2% of people are vegetarian, say the authors.
And many people rely on livestock products to eat a healthy balanced diet. The nutrients for which needs were the most difficult to fulfil for high GHGE reductions included potassium and calcium (found especially in dairy foods).
‘… while vegetarian or vegan diets are often claimed to reduce the environmental impact of diet, the results of the present study suggest that food group diversity must be preserved to improve diet sustainability, rather than drastic dietary changes excluding food categories.’ – Perignon M et al, 2018.
The authors conclude that studies looking at changing diets to reduce the impact on the environment should always take on board the importance of balancing cuts in greenhouse gases with our nutritional needs.
