Can sustainable diets help reduce carbon emissions?

Opinion: a truly sustainable diet needs to be adapted not only to each individual, but also must change throughout their life

by Katie DaviesUCD

The way we produce and eat food is unsustainable from health and environmental perspectives. We have to have food, but the scale and method of food production is widely recognized as unsustainable. Land use, water use and greenhouse gas emissions are just some of the metrics that describe the environmental impact of food production.

Producing food takes about 40% of available land on earth. It’s responsible for 70% of total freshwater usage and emits at least 30% of global greenhouse gas emissions annually. This means that agriculture and food production must play a critical role in meeting climate pledges, like Ireland’s legally binding pledge to reach net-zero carbon emissions by 2050.

Agriculture is Ireland’s largest emitter of greenhouse gases, generating over 37% of the country’s total emissions. High greenhouse gas emissions are the result of both large-scale food production and what we chose to produce. A report by the Eat-Lancet Commission suggests that we will cause irreversible environmental damage in less than 30 years without large-scale changes to food production and emissions. Food production inevitably produces some greenhouse gas emissions, but there is scope for reduction.

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From RTÉ Radio 1’s Today With Claire Byrne, discussion on Irish agriculture and emissions targets with Oisin Coughlan from Friends of the Earth Ireland and Justin McCarthy from the Framers Journal

Recommendations for sustainable diets are often driven by a food item’s ‘carbon footprint’ or the amount of greenhouse gases associated with the production and transport of that food. Animal products, like meat and dairy, produce more emissions on average compared to plant-based foods. Therefore, proposed sustainable diets are rich in plant-based foods like whole grains, fruit, vegetables, nuts, and legumes and lower in animal source foods, particularly red and processed meats. Research suggests that greenhouse gas emissions can be reduced simply by opting for foods with lower carbon footprints.

Encouraging intakes of plant-based foods is nothing new. Food-based dietary guidelines, like the HSE’s Healthy Eating Guidelines recommend high intakes of whole grains, fruits, vegetables and other plant-based foods as part of a healthier diet. The way we are producing food risks both the health of the planet and our own health as well. Unhealthy diets now lead to more poor health than drug use, tobacco use and alcohol intake combined. Diets with high intakes of vegetables, whole grains and other plant-based foods are associated with lower risk of disease and better health. Therefore a move to a more sustainable diet, may be more beneficial for planetary and human health.

However, meat and dairy provide vital micronutrients like vitamin B12, iodine, zinc and calcium. Current evidence suggests lower greenhouse gas emitting diets have lower nutritional adequacy, meaning they may not be able to provide healthy amounts of all essential nutrients. plantonly diets—such as a strictly vegan diet—have inadequate levels of essential nutrients, meaning they are not nutritionally complete without supplementation. Therefore, to receive all essential nutrients through the diet, it is important to eat a variety of foods from both animal and plant sources.

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From RTÉ 2fm’s Jennifer Zamparelli show in 2019, dietitian Orla Walsh on the vegan diet

There is no clear guidance on how to make an individual’s diet sustainable. Sustainable diets are defined by the Food and Agricultural Organization of the UN (FAO) as one that “promotes all dimensions of individuals’ health and wellbeing; have low environmental pressure and impact; are accessible, affordable, safe and equitable; and are culturally acceptable “. By this definition, diets that are healthy and sustainable would differ by country as well as across different populations.

Recent nutrition research shows that people respond differently to diets due to a variety of factors including personal lifestyle choices and demographic characteristics. Our nutritional needs change throughout our life span with factors like age, body size and physical activity levels influencing what our bodies need.

For example, children or older adults require higher intakes of some critical micronutrients such as calcium to support healthy growth or bone health. Alternatively, someone who is very physically active may need a higher proportion of carbohydrates in their diet compared to someone who is less active. For a diet to be truly sustainable, it needs to be adapted not only to each individual, but also must change throughout an individual’s lifespan.

There is no clear guidance on how to make an individual’s diet sustainable

Evidence to date on sustainable diets is limited and theoretical. No clinical trials have tested the effectiveness, safety and acceptability of a more sustainable diet. While some recommended diets have been published, there is evidence that some recommendations wouldn’t meet nutrient requirements for all adults. While nutrition research can model a better diet and predict what will happen, there is no way of knowing until it is actually tested.

The MyPlanetDiet study aims to critically examine what a sustainable diet is and if diet-related greenhouse gas emissions can be reduced in a safe and acceptable way. The study is the first human trial globally which tests the effects of a more sustainable diet and we are currently recruiting volunteers.

Katie Davies is a PhD candidate in the Institute of Food and Health at UCD. Her research aims to test the effects of more sustainable diets under the SuHeGuide project which is a collaboration between Teagasc, UCD Institute of Food and Health, Queen’s University Belfast Center for Public Health and UCC School of Food and Nutrition.


The views expressed here are those of the author and do not represent or reflect the views of RTÉ


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