Woman selling fresh vegetables at market in Kota Baru, Malaysia.
Technical Summary

Plant-Rich Diets

Project Drawdown defines a plant-rich diet as the individual dietary choice: to 1) maintain a 2250 calorie per day nutritional regime; 2) meet daily protein requirements while decreasing meat consumption in favor of plant-based food items; and 3) purchase locally produced food when available. This solution replaces projected regional dietary trends.

Plant-rich diets hold enormous potential for climate change mitigation if adopted on a global scale, but anyone wishing to make global diets more sustainable will be working against established dietary trends. Global dietary preferences – in particular those related to meat, fish, and dairy products – will continue to be a key driver of both agricultural and land-use related emissions. Implementation of a plant-rich diet can be readily adopted even with small behavioral changes that can have a significant effect globally. In terms of cost, the solution appears to yield significant savings at the individual level, and indirectly at the national level through lower healthcare costs. Moreover, the burden of change seems highly equitable and implementable, because developing nations already consume fewer calories and do not need to shift their diets much, whereas developed nations need to address issues such as obesity.

Methodology

To evaluate the impact of a plant-rich diet, an independent model was created outside Drawdown’s core model framework to project food consumption and waste from 2020-2050. This was required due to the complexity of estimating country- and regional-scale food consumption and waste trends based on reported commodity types along the supply chain.

Total Addressable Market

The global market for a plant-rich diet is defined as the total demand for food, based on estimated kilocalories supplied per year for consumption by the world’s population. The baseline food consumption is projected for all countries up to 2060 in kilocalories per capita per year, using data compiled by the Food and Agriculture Organization (FAO) for the year 2013.[1] Future consumption is forecasted using growth factors from Alexandratos et al. (2012), which reflect projected dietary changes.[2]

Adoption Scenarios [3]

Impacts of increased adoption of plant-rich diets from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the food demand reflects future “business-as-usual” dietary changes based on projected regional growth factors for available food categories (Alexandratos et al., 2012).[4]

The adoption of a plant-rich diet assumes the following criteria are met:

  1. Adopting an individual daily nutritional regime of 2250 kilocalories per day;
  2. Consuming reduced quantities of meat-based protein (particularly red meat, which is constrained to 57 grams per day);[5]
  3. Purchasing locally produced food when possible (a 5 percent localization factor is applied globally).

Adoption scenarios in this model grow linearly over time starting from the base year of 2014, and are considered “complete” in 2050. Linear growth trends were chosen because of the lack of country or regional data; additional behavioral research at more granular scales can reveal more representative adoption estimates.

For plant-rich diet, three scenarios were developed:

  • Scenario 1: This scenario assumes that 50 percent of the global population will adopt a plant-rich diet by 2050.
  • Scenario 2: In this scenario, adoption will reach 75 percent of the global population by 2050.

Emissions Model

To estimate emissions, commodity-specific carbon dioxide-equivalent per-calorie values were drawn from several sources (see Audsley et al., 2010; Heller and Keoleian, 2014; Hoolohan et al., 2013; Tilman and Clark, 2014; Vieux et al., 2012) to determine minimum, average, and maximum estimated emissions factors per commodity. The emissions factors were multiplied by the baseline annual food demand by country and commodity to get the carbon dioxide-equivalent values for food items over time. Emissions estimates were aggregated by commodity types[6] and regions classified by the FAO (2011), and are aligned with regions used by Project Drawdown.

Emissions reductions are calculated based on the incremental adoption of plant-rich diets. This figure is subtracted from the emissions associated with the Reference Scenario, and resulting net emissions reductions are aggregated to represent the total global reduction from avoided agricultural production.

Integration

Project Drawdown calculates the total change in food demand by weight (in million metric tons) by commodity type. It is assumed that reduced demand in countries with consumption trends higher than 2250 kilocalories per capita per day can be diverted to feed current and future undernourished populations. Diverted tonnage of food is used as an input in the Project Drawdown Integrated Yield Model, which combines all agricultural production models to determine the required yield to meet the estimated food and bio-based product demand on an annual basis. Results from all demand-side solutions, i.e. reduced food waste and plant-rich diet, determine the need for land conversion to cropland and grassland in order to meet future food demand. Emissions reductions associated with land conversion are applied to both reduced food waste and plant-rich diet according to the proportion of their contribution to diverted food supply.

Results

Between 2020 and 2050, the Scenario 1 projects the total cumulative emissions reduction from adopting a plant-rich diet to be 65.02 gigatons of carbon dioxide-equivalent gases: 43.01 gigatons due to diverted agricultural production, 21.78 gigatons from avoided land conversion, and 0.23 gigatons from sequestration from ecosystem protection.

The Scenario 2 avoids emissions by a total of 91.72 gigatons: 68.32 gigatons due to diverted agricultural production, 23.16 gigatons from avoided land conversion, and 0.24 gigatons from sequestration from ecosystem protection.

Discussion

The reality of high per-capita meat consumption in high-income countries, paired with global diets that are forecasted to look increasingly western, creates one of the most fundamental challenges of plant-rich diet adoption. How can we reduce livestock production in the face of high and rapidly increasing demand? Achieving some dietary change is reasonable, but more dramatic changes will be difficult to implement globally.

Scaling plant-rich diets globally is a challenge of communication and education as much as it is one of policy. Among the most fundamental research findings on this topic is that healthier diets tend to also be low-emission diets (Bajželj et al., 2014; Tilman and Clark, 2014; Stehfest et al., 2009). While plant-rich diets are not necessarily the lowest-emission diets, they represent a significant improvement over current dietary practices, particularly those in countries like the USA and Australia where meat (and especially beef) consumption is high. This overlap in desirable outcomes (healthier population, lower emissions) is a powerful communication and policy tool, particularly given that individuals are more likely to respond favorably to messaging that affects their health than they are to messaging relevant to their environmental impact.

 

[2] The projected dietary changes show significant impacts for countries like India and China, whose populations are expected to demand more carbon-intensive foods over the next 30 years.

[3] For more on Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Food Sector-specific scenarios, click the Sector Summary: Food link.

[4] The Reference Scenario is equivalent to the total addressable market for food demand.

[5] The caloric breakdown of plant-rich diet comes from Bajželj et al. (2014). This breakdown takes projected regional data and optimizes it according to a number of nutritional studies to comprise a “healthy” diet.

[6] Commodity types include: cereals, roots and tubers, oilseeds and pulses, fruits and vegetables, meat, fish and seafood, and milk.