Contribution of food choices to climate change

Food and dietary choices can have an impact on the environment in many ways, such as climate change, land, water and energy use, and biodiversity, but the focus of this paper is on climate change, specifically GHGE. Climate change is the result of the emission of greenhouse gases into the atmosphere which causes global warming^{( 12 )}. Greenhouse gases, defined under the Kyoto protocol, include CO₂, CH₄, N₂O and refrigerant-type gases (e.g. hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride), and are collectively known as CO₂ equivalents^{( 13 )}. These gases vary in their impact on global warming, with CH₄ being about twenty-five times more potent, N₂O 296 times more potent and the refrigerant gases being many thousands of times more potent than CO₂. Some of these gases do occur naturally, but the increase in the global temperature seen in the past century correlates to an equally dramatic rise in GHGE resulting predominantly from human activities^{( 12 )}.

There is an urgent global need to mitigate GHGE to limit further climate change but at the same time address the challenges of food security and an increasing global population with finite natural resources. Beddington described the future food security scenario of climate change, diminishing water and energy resources and the increasing population and urbanisation as the ‘perfect storm’ of global events, and ‘ …that by 2030 the world will need to produce around 50% more food and energy, together with 30% more fresh water, whilst mitigating and adapting to climate change.’⁽ Reference Beddington ^{14 )}. The UK passed the Climate Change Act in 2008, which set legally binding targets to reduce GHGE by 80% by 2050, with an interim target of 34% by 2020 (targets are set against 1990 emission levels)^{( 15 )}. Similar legislation was passed in Scotland in 2009, but with a higher interim reduction target of 42% by 2020. These targets provide a clear message that action is needed, but they are production-based emission targets (include only goods and services produced within the UK) and do not include goods and services imported into the UK, which is particularly important when considering the GHGE of the diet. For example, the UK imports approximately twice as much beef as it exports but the imported meat consumed in the UK is not counted in the UK GHGE production targets. For the true impact of the diet it is important that the total GHGE is based on food consumed in the UK, not just food produced in the UK.

It is estimated that the food supply chain accounts for approximately 18–20% of the annual GHGE in the UK (consumption-based emissions), with meat and dairy products having the highest contribution to these emissions⁽ Reference Garnett ^{16 )}. This increases to more than 30% if land use change is included⁽ Reference Audsley, Brander and Chatterton ^{17 )}. GHGE occurs at every stage of the food chain (referred to as the lifecycle of a product) from agricultural production through to consumption and disposal of waste food. Figure 1 shows a simplified version of where emissions occur across the life cycle, as well as where nutritional changes can occur, which can be used to identify where GHGE can be reduced or nutritional quality improved. Reductions in GHGE are being made at the food production stage (e.g. agriculture, production methods, transportation and reduction of waste), but there are practical limitations beyond which it is impossible still to produce food. Consumers therefore also need to play a significant role in the reduction of GHGE through modification of their dietary patterns and food choices.

Fig. 1. Environmental impact of food and nutritional changes throughout the food chain.

Variation in greenhouse gas emissions by food groups

GHGE vary significantly between different foods groups, but also within food groups. Despite the uncertainties in estimating GHGE, the general hierarchy of the GHGE for the broad food groups is accepted to be relatively consistent; animal-based products tend to have higher emissions than plant-based foods (by weight of food). GHGE can, however, vary quite significantly for the same food depending on farming methods (e.g. intensive v. extensive), geographic region (e.g. UK v. other countries), transport method (e.g. air freighted v. shipped) and the growing conditions (e.g. outdoors v. heated glass houses)⁽ Reference Garnett ^{16 )}. For example, it is estimated that tomatoes produced in the UK in heated glasshouses using fossil fuels can have a GHGE 5–6 times higher than those produced outdoors in Spain and transported by road to the UK⁽ Reference Audsley, Brander and Chatterton ^{17 )}. Similarly meat from intensively reared livestock can have lower GHGE because of the faster rate of growth of the animal and therefore a shorter lifetime (less CH₄ and manure produced). There are obviously other issues such as animal welfare, water use (e.g. using irrigation systems in water scarce area), and economic viability (e.g. extending production beyond the natural growing season by using heated glasshouses) that need to be taken into consideration.

The highest GHGE are associated with ruminant animals due to CH₄ produced during digestion and N₂O from the manure, and both of these gases are much more potent than CO₂ ⁽ Reference Garnett ^{16 )}. Using national dietary surveys it has been shown that meat and meat products are consistently the most significant contributors to GHGE in the diet in many developed countries⁽ Reference Vieux, Darmon and Touazi ^{18 –} Reference Macdiarmid, Kyle and Horgan ^{20 )}. These observations have driven recommendations to reduce intakes of meat and dairy products in order to lower the GHGE, but these types of changes must consider the nutritional implications and ensure that there are no detrimental consequences for the health, e.g. Fe or Zn status. Equally, any proposed changes needs to be realistic in terms of acceptability and cost if they are to have any prospect of achieving dietary changes. Given that less than 2% of the UK population report being vegetarian, and even fewer being vegan⁽ Reference Bates, Lennox and Bates ^{8 )}, it would be unrealistic to suggest a meat-free diet.

Is a healthy diet an environmentally sustainable diet?

There is not a simple answer to this question because of one of the fundamental differences between defining a healthy diet and a diet with a low environmental impact. A healthy diet is principally about the nutrient intakes, which can be achieved from many different combinations of foods. In contrast, GHGE are associated with food items for which the nutrient content can vary. Taking for example protein, there are dietary reference values for minimum intakes of protein, and this can come from animal- or plant-based proteins, but the choice made will vary significantly in terms of GHGE. This is the same even for food-based dietary recommendations, such as fruit or vegetables which can have very different GHGE depending on the product selected. In that sense it cannot be assumed that a healthy diet meeting nutrients requirements will necessarily have low GHGE as it will depend on the specific foods in the diet.

One of the first studies to investigate whether it was possible to have a realistic diet that met dietary requirements for health and minimise the GHGE from the diet showed that it was possible to meet recommendations for energy and macro- and micronutrients^{( 21 )} while selecting foods that would minimise the GHGE of the diet (approximately a third lower)⁽ Reference Macdiarmid, Kyle and Horgan ^{11 –} Reference Macdiarmid, Kyle and Horgan ^{20 )}. This was achieved without eliminating meat and dairy products from the diet, although the quantity of meat was reduced considerably compared with current intakes reported in the National Diet and Nutrition Survey, and the type of dairy products tended to be reduced fat versions. It was possible to create diets with even lower GHGE (up to 90% reduction) while still achieving dietary requirements but the range and quantities of foods were completely unrealistic (i.e. only seven food items and all in unrealistic quantities). This study demonstrated that a healthy diet can be compatible with one that is significantly lower in GHGE.

This, however, should not be interpreted that a healthy diet will always have lower GHGE. Using the ‘healthy, low GHGE’ diet described earlier⁽ Reference Macdiarmid, Kyle and Horgan ^{20 )} comparator diets were created by swopping the food items for ones higher in GHGE or for less healthy items while maintaining the same dietary pattern and total energy intake (Table 1). It was possible to create a diet that met dietary requirements but had almost double the GHGE by using fruit and vegetables with high GHGE, rice rather than pasta or potatoes (rice produces CH₄) and increasing the amount of red meat (not exceeding the maximum recommended intakes). Conversely, it was possible to create a diet very low in GHGE based on high intakes of sugar and refined carbohydrates, with only small amounts of meat, fruit and vegetables (‘unhealthy, high GHGE’). Finally, a diet was created with a high meat and protein content, and only small amounts of complex carbohydrates, fruit and vegetables which was very high in GHGE and did not meet dietary requirements (‘unhealthy, high GHGE’). These are only examples of diets, but they serve to illustrate that it cannot be assumed a healthy diet will be lower in GHGE. Population studies have shown that distribution of GHGE coming from individual dietary intakes is very wide⁽ Reference Vieux, Darmon and Touazi ^{18 ,} Reference Coley, Goodliffe and Macdiarmid ^{23 )}.

Table 1. Scenarios to illustrate the variation in greenhouse gas emissions (GHGE)** of achievable healthy diets that meet nutrient requirements and unhealthy diets that fail to meet nutrient requirements

* SACN Dietary Reference Values for Energy^{( 22 )} and Department of Health Dietary Reference Values for an adult woman^{( 21 )}.

** GHGE include only up to the point of the regional distribution centre (not full lifecycle analysis) but are adjusted for the food as eaten.

Changing dietary patterns and food choices for health and the environment

As we move closer to understanding some of the principles of a healthy and lower environmental impact diet, the challenge is to change dietary patterns and food choices of the population. Historically, attempts to improve dietary intakes have been relatively unsuccessful despite the positive impact of a healthy diet for an individual. Changing dietary intakes to limit the damage to the environment is likely to prove even more challenging, particularly as there is no obvious immediate personal gain. A recent study exploring different ‘pro-environmental behaviours’ (behaviours included: limiting the number of flights taken; recycling; reducing food waste; reducing energy use; installing insulation; eat more local/seasonal food; limit water usage; use cars less for short trips; use vehicles more efficiently renewable energy systems) showed that adopting a lower environmental impact diet was a change people thought they were most able to make, but it was the change they were least willing to make (<10% population sample)^{( 24 )}. Another survey of 3000 adults in the UK revealed that only 15% of people would change their diet for the benefit of the environment^{( 25 )}. Interestingly, in contrast they said that were more willing to cut down the amount of red meat in their diet than reduce their intake of dairy products (63% v. 45%), but putting this into context 76% said they would be willing to reduce their consumption of confectionery.

The concept of a sustainable diet is complex and therefore open to misinterpretations. Studies suggest that there is a relatively high awareness among the population that food production has an impact on climate change (56%), but <20% of respondents said that they would know how to change their diet to one that is more sustainable^{( 25 )}. The most commonly cited diet-related behaviours that people think would be beneficial to the environment are avoiding excessive packaging, purchasing locally produced food, eating organic food and reducing food waste⁽ Reference Lea and Worsley ^{26 ,} Reference Tobler, Visschers and Siegrist ^{27 )}. Significantly fewer people think changing their diet could have an impact. Lea & Worsley⁽ Reference Lea and Worsley ^{26 )} reported that >85% of people thought that using less packaging and purchasing locally produced food would benefit the environment, compared with only 22% who thought that eating less meat would be beneficial. Similarly, Tobler et al. ⁽ Reference Tobler, Visschers and Siegrist ^{27 )} reported that people rated eating less meat to have the least benefit to the environment. This suggests that there is scope to provide information, but at the same time recognising that this is unlikely to be sufficient to change behaviour.

Dietary changes that could benefit both the health of the population and the environment

Two proposals to reduce GHGE are to reduce intakes of meat (and dairy products) and to reduce overconsumption by only eating sufficient energy required to maintain a healthy weight^{( 4 ,} Reference Garnett ^{16 )}. These could both have benefits for health and the environment.

Where are the potential conflicts between health and the environment?

Tackling obesity and reducing intakes of meat have potential co-benefits for health and the environment, but this is not the case for all aspects of the diet. The most widely recognised conflict between health and environmental sustainability is the dietary recommendation for fish intake. Fish is recognised as a good source of protein and oily fish are high in n-3 fatty acids, which forms the basis for the current recommendation of two portions of fish per week (one of which should be oily fish)^{( 39 )}. The issue is whether the current and future stocks of fish are sufficient if the population were to eat their recommended intake of oily fish, which they currently do not meet⁽ Reference Bates, Lennox and Bates ^{8 )}. Technological solutions (e.g. aquaculture) are being sought to increase the supply of fish and developing aquaculture has been suggested as one of the potential actions for future global food security⁽ Reference Godfray, Beddington and Crute ^{40 )}. Efforts to increase fish supplies as a source of sustainable protein, however, need to be done in conjunction with encouraging more people in the UK to eat fish as part of their diet. The average intake of fish among adults in the UK is only 58 g/week, which is equivalent to about 41% of the recommended intake, with many people eating no fish at all⁽ Reference Bates, Lennox and Bates ^{8 )}. There is also confusion among consumers about the sustainability of eating fish, despite the introduction of labelling of fish from sustainable sources and media campaigns⁽ Reference Clonan, Holdsworth and Swift ^{41 )}. This is a good example of where a single consistent message about health and the sustainability of foods is needed otherwise the consumers will simply disengage.

Other more subtle conflicts can arise as a result of dietary recommendations for a healthy diet. In the dairy sectors for example, GHGE are relatively high compared with plant-based foods but dairy products can provide essential nutrients in the diet. However, they also contribute significant quantities of SFA and therefore consumers are recommended to eat lower fat dairy products. The majority of the population adheres to this, with only 20% of the adult population consuming whole milk⁽ Reference Bates, Lennox and Bates ^{8 )}. Removing the cream from dairy products creates an economic dilemma for producers and an environmental issue in terms of food waste if it cannot be used elsewhere. For health, it is counterproductive if all of the fat removed simply re-enters the diet in the form of other processed foods (e.g. ice-cream, cakes and ready meals). So, the question is how can this type of by-product be used for non-dietary purposes without creating a negative environmental impact? In the meat industry, there are similar issues for food waste if we only consume the lean meat from the animal and not the entire animal (e.g. offal). Duchin⁽ Reference Duchin ^{42 )} draws attention for the need to factor in the environmental impact of increasing production of fruit and vegetables to supply the recommended intake of five-a-day, given the water and climatic constraints in many countries supplying these products and the seasonality for fresh produce. These examples serve only to illustrate the potential of unintended consequences if the food and dietary recommendations for health and the environment are considered in isolation and highlight the importance for working together.

Summary

Returning to the question posed at the start, ‘Is a healthy diet an environmentally sustainable diet?’ this paper has attempted to show the complexity of the answer and illustrated that general assumptions cannot be made. The discussion focused on GHGE and climate change, but it is important to return to the Food and Agriculture Organization definition of a sustainable diet and can consider the other environmental, social and economic elements. Understanding about the environmental impact of food choices is increasing but the major challenge remains to change the current unhealthy and unsustainable dietary patterns of the UK population that have become well established over decades. It is recognised that substantial changes will also need to be made to agricultural and food industry practices to change the food environment, but this should not be seen as an alternative to individuals changing their dietary patterns as action is needed in all sectors⁽ Reference Duchin ^{42 )}. Furthermore, to tackle this immense problem will require working together across disciplines, and as proposed by Godfray et al. when he referred to tackling these issues in terms of food security: ‘Navigating the storm will require a revolution in the social and natural sciences concerned with food production, as well as a breaking down of barriers between fields.’⁽ Reference Godfray, Beddington and Crute ^{40 )}