Since the early 1900s, a subset of wealthy elites with a Malthusian mindset have been convinced that the world is overpopulated. Rather than let poor people starve, as British policy in the home of Malthus advocated, later generations sought to breed out the poor with eugenics, and forced sterilization. After World War II made eugenics wildly unpopular, proponents reframed their ideas as "population control." Groups like Planned Parenthood, Sierra Club and Environmental Defense Fund were all founded by former eugenics advocates. Their supporters, like Paul Ehrlich and John Holdren, also advocated forced sterilization and abortion, to limit population. 

But for the most part those efforts have failed and so more recently those claims were repurposed again, this time as vegetarianism. 

A new "food-print" model, using ten different scenarios ranging from the average American diet to a purely vegan one, estimated that agricultural land in the contiguous U.S. could have the capacity to feed up to 800 million people, twice what can be supported based on current average diets now.

They posit in Elementa that a vegetarian diet that includes dairy products could feed the most people from the area of land available. They don't agree with the goal of simply increasing production and yield and believe limiting consumption is also a strategy to feed the future. 

The ten dietary scenarios varied by the sources of protein, though eight of the diets complied with the controversial 2010 Dietary Guidelines for Americans. A baseline diet represented the country's current food consumption--higher in meats, grains, fats and sweeteners than the other dietary scenarios. In the baseline diet, roughly 80 percent of available cropland was used to grow crops for animal feed, such as hay, while the other 20 percent was devoted to fruits, vegetables and grains for human consumption.

The remaining dietary scenarios ranged from 100 percent of the population eating an omnivorous diet (a balance of meat and plant-based foods), to 100 percent of the population eating a vegan diet (no meat or by-products such as milk, eggs and honey). Intermediate scenarios included varying proportions of omnivores and vegetarians, and the accompanying cropland usage varied accordingly.

They found that:

• A lacto-vegetarian diet (a vegetarian diet that includes dairy products) had the highest carrying capacity, meaning that it could feed the most people per current land devoted to farming.

• Diets including some meat can feed more people than vegan diets, depending on estimates of how much land is suitable for crop cultivation.
• The baseline diet required eight times more land than a vegan diet.
• The overall results from the model estimate that U.S. agricultural land has the capacity to meet the needs of a population 1.3 to 2.6 times larger than the U.S. population in 2010.

To develop the model, the team began with an estimate of hypothetical food intake by food group. They then worked backwards to calculate the food quantity that must be produced, the agricultural raw material needed to produce those foods, the total land requirements, and the number of people who can be fed from the land used to produce those foods. 

The model tried to account for factors such as the suitability of cropland for cultivation, the interdependencies of dairy and meat production, and the use of coproducts of food production to feed livestock. 

Other studies have shown that if other countries simply adopted America's scientific approach to agriculture, either land equivalent to that of India could revert to nature, or we could feed three billion more people without sacrificing any food types.