The Role of Animal-Source Foods in Healthy and Environmentally Sustainable Diets

Scientific and political debates around the role of Animal-Source Foods in healthy and environmentally sustainable diets are often diverging. Animal-Source Foods, such as meat, milk, fish and eggs, have many positive health effects when consumed in the recommended amounts. They represent a key strategy for addressing undernutrition in low- and middle-income countries thanks to their richness in commonly lacking nutrients. For these reasons, scientists are increasingly debating the role of Animal-Source Foods and clarifying the evidence of their health and environmental benefits and risks. A Critical Review published in the Journal of Nutrition by Anne Mottet discusses the health benefits of Animal-Source Foods and their health risks. The article also focuses on their environmental benefits and risks, andreviews evidence on alternative proteins and protein-rich foods.

It is well established that Animal-Source Foods are dense in bioavailable nutrients and can contribute to food and nutrition security. For example, they are the only intrinsic food source of vitamin B12 and contain more bioavailable forms of vitamins A and D, iron, and zinc than plant-source foods. Deficiencies of these micronutrients during critical stages in a person’s life can have severe and lasting consequences, including congenital disabilities, anaemia, reduced growth, cognitive impairment, increased susceptibility to infections, rickets, decreased work productivity, blindness, and even death. The paper points out that many Sub-Saharan African and South Asia populations could benefit from their increased consumption through improved nutrient intakes and reduced undernutrition.

When produced at the appropriate scale and following local ecosystems and contexts, Animal-Source Foods can play an important role in circular and diverse agroecosystems that, in certain circumstances, can help restore biodiversity and degraded land and mitigate greenhouse gas emissions from food production. Livestock grazing and feed production can positively and negatively affect soil health. Livestock manure moves organic matter, nutrients, and water within agroecosystems, increases crop productivity, and many studies have shown a consistent increase in soil organic matter with manure application. Consequently, manure application limits the decline in soil fertility, which is one of the biggest challenges in maintaining healthy soils.The direct and indirect use of water is one challenge often raised when looking at impacts of  livestock. 94% of the water used by livestock represents “green water” from rainfed conditions, and more than one-third of green water comes from the production of pastures. Therefore, pasture-based livestock production can be a method to productively use this green water, which would fall on the land with or without livestock. This is particularly relevant for pastures on marginal land, which do not compete with cropland for water.

Beef cattle account for 33% of water use, dairy animals 18%, and pigs 14%. As such, the contribution of livestock’s use of water from irrigation (blue water) to the total water use is relatively low: 6% for broilers and 14% for pigs.

Under specific circumstances, habitat modification can benefit biodiversity by maintaining natural grasslands. For example, in Europe, grassland habitats are among the ecosystem types with the highest biodiversity levels because the long history of livestock farming has provided time for a large pool of species to adapt to specific conditions.

Regarding climate change mitigation and adaptation, the importance of livestock is well recognized by policymakers. The Intergovernmental Panel on Climate Change (IPCC) special report on climate change and land for example found with high confidence that “supply-side practices can contribute to climate change mitigation by reducing crop and livestock emissions, sequestering carbon in soils and biomass, and decreasing emission intensity within sustainable production systems”.

But nobody is resting on their laurels, so the FAO has identified three main strategies for climate change mitigation of livestock:

1. Improve efficiency and productivity;
2. Better integrate ruminants in the circular bioeconomy, enhancing coproducts from crop processing and crop residues as feed and recycling energy and nutrients from manure;
3. Increase soil organic carbon content, particularly in pastures, through improved grazing management.

It is estimated that a 14%–41% reduction in greenhouse gas emissions from the livestock sector is possible if all producers adopt the technologies and practices currently used by the most efficient producers.

Livestock consumes one-third of the global cereal production as feed, which is 11% of total feed; the rest is mostly composed of plant material with no or limited other direct food use, such as grass, crop residues, and coproducts from crop processing. The specialized digestive tract of ruminants allows them to convert these fibrous plant materials into human-digestible high-quality protein, adding value to the products that might otherwise go unused. Such non-food products as livestock feed can contribute to biomass and nutrient recycling.

Using manure as fertilizer, livestock production recycles nutrients and organic matter. The total nutrients available from livestock manure exceed those from synthetic fertilizers, covering more than 80% of agricultural plants’ nitrogen and phosphorus requirements globally. Integrating crops and livestock can reduce the need for inputs such as land, water, and nutrients and improve overall efficiency.

Better circularity can be achieved by increasing the share of livestock feed consisting of grass, crop residues, and coproducts from processing humans cannot consume. And recycling and recovering nutrients and energy from animal waste include the application, composting, and anaerobic digestion of manure for biogas production. Circular livestock systems have the potential to provide a significant share of daily protein requirements (50–60 g), and they could supply 9 to 23 grams of edible protein per person per day if all food waste could be recycled as animal feed.

There is no one-size-fits-all approach, no general or averageamount of Animal-Source Foods  that are healthy and environmentally sustainable. It depends on the local context and health priorities and will inevitably change over time as populations develop and as nutritional concerns evolve.

Efforts by governments and civil society organisations to increase or decrease consumption of animal source foods should involve the local stakeholders impacted by potential changes. Policies, programmes, and incentives are needed to ensure best practices in production, curb excess consumption where it is high, and sustainably increase consumption where it is low.