Efficiency of a Plant-Based Diet

If humans eat vegetables directly, the energy efficiency is much higher than when cattle are fed feed and then humans eat beef. There are various ways of calculating efficiency, so the specific figures differ, but the consistent conclusion across many sources is that vegetarianism is more efficient. In this article, I will summarize and introduce the contents of the related paper published in 2016, Energy and protein feed-to-food conversion efficiencies in the US and potential food security gains from dietary changes. The data are based on the United States, but they can also be applied to Korea and most other industrialized countries.

Energy efficiency

Feed conversion ratio

One of the concepts traditionally used is feed conversion ratio (FCR). Feed conversion ratio is a figure that indicates the ratio at which the feed eaten by livestock is converted into body mass. For example, if the feed conversion ratio is 2, that means when 200 g of feed is eaten, 100 g of body mass is produced.

However, even animals of the same species tend to grow faster when they are young, so FCR varies depending on how many weeks have passed since birth (that is, age in weeks). It also varies depending on whether the weight standard is the weight of the live animal, the weight of the carcass after slaughter with the organs and bones removed, or the weight of the meat as finally packaged and delivered to consumers. Because there are so many variables, its accuracy is low.

The following are the average feed conversion ratios for cattle, pigs, and chickens according to American USDA standards (based on the weight of meat delivered to consumers).

Cattle require the most feed to obtain the same amount of meat, and pigs are next. Chickens require relatively less. Of course, the best method is for humans to eat a vegetarian diet directly.

Calories and protein

It is a bit more accurate to calculate how efficiently the energy in feed is converted into meat than to use feed conversion ratio. The 2016 paper calculates energy efficiency on the basis of calories and protein.

The figures above show what percentage of the energy (or protein) in feed is converted into edible animal products. Feed conversion ratio is better when lower, but energy efficiency is better when higher. Once again, cattle are the least efficient and chickens are the most efficient. And once again, of course, the most energy-efficient method is for humans to eat a vegetarian diet directly.

Efficiency when growing crops for humans to eat instead of feed

The paper calculates how many more people could be fed while maintaining the average American’s intake of protein and calories if, on the land used to grow cattle feed, chicken feed were grown instead and chickens were raised. In addition, it performs the same calculation for the case of growing crops for humans to eat instead of cattle feed and adopting a vegetarian diet.

For reference, the average daily American intake used in the paper is 2500 kcal and 70 g of protein. The US population was regarded as about 300 million.

If people eat chicken instead of beef, enough additional food can be produced to feed an extra 120 million people (on a calorie basis, about 40% of the population) or 140 million people (on a protein basis, about 47% of the population).

If people adopt vegetarianism instead of beef (mainly a bean-based diet), enough additional food can be produced to feed an extra 190 million people (on both a calorie and protein basis, about 63% of the population).

Efficiency is not everything

The figures above are efficiency from the perspective of land and energy, and the number of animals who die moves in the opposite direction. The edible portion obtained from one cow is several hundred kilograms, whereas one chicken yields only about 1-2 kilograms, so if the same calories are obtained from chickens instead of cattle, the number of individuals killed increases by several dozen times (reference: Slaughter statistics). Moreover, chickens are among the animals that suffer the most in factory farming due to stocking density and selective breeding.

From the perspective that takes the total sum of suffering experienced by individuals as the standard (Singer’s utilitarianism), “chickens instead of cattle” makes things worse rather than better. It should be kept in mind that the paper above is, from the outset, a study dealing with food security and land use, not animal ethics.

Conclusion

Vegetarianism or a vegan diet is not only ethical but also environmentally friendly and the most energy-efficient.