May 27, 2019

The role of livestock in nutrition—looking beyond calories

The role of livestock in nutrition—looking beyond calories

As groups like the EAT-Lancet Commission are claiming that global health and the environment would improve with policies to support a more plant-based diet, it’s important to take a closer look at the actual nutritional value of animal products.

In a commentary published in the July/August 2018 issue of Nutrition Today, Donald Keith Layman, professor emeritus in the University of Illinois Department of Food Science and Human Nutrition, sums up the benefits of ruminants in a sustainable food system.

Layman starts by explaining why calories are not the best way to measure food quality.

“Initial attempts to measure the impact of agriculture on the environment used a metric of greenhouse gas emissions/kcal of food produced to assess the relative impact of different foods and agriculture practices,” Layman writes. “This metric highlights the differential costs for production of grains versus livestock and led to conclusions that livestock have disproportionate negative impacts on the environment, leading many researchers and policy makers to call for a shift toward more plant-based diets. However, this metric implies that production of calories is the most important diet criterion and has been criticized for ignoring diet quality.”

Instead of focusing on calories, Layman shows the importance of animal protein as a foundation for a healthy, sustainable diet.

“Currently, livestock produces more than one-third of the world’s protein, and ruminant animals (ie, cattle, sheep and goats) have the unique capacity to convert nondigestible biomass (ie, grasses and forages) into high-quality protein,” writes Layman. “These factors highlight the need for prudent use of ruminants to optimize land use for production of adequate quantity and quality of protein.”

As cattle consume these feedstuffs, they convert it into meat and milk that provide nutrients that are “bioavailable,” meaning more easily taken up by the body. Plants cannot replicate nutrient-rich animal products.

“Some plants such as bean and lentils are good sources of protein, but all plants have low protein density and are limiting in 1 or more of 5 of the essential amino acids (EAAs) (ie, lysine, methionine, tryptophan, threonine, and leucine),” writes Layman.

Confronting Misconceptions

So where did so many people get the idea that animal agriculture—which provides healthy diets to billions—is unsustainable?

Layman encourages readers to weigh regional differences in greenhouse gas emissions (GHGEs). Smaller, more rural countries do tend to have higher emissions from agriculture, and these countries skew the global numbers.

For example, only 4.2% of GHGEs in the United States come from livestock, compared with 31% from electricity production, 27% from transportation, 21% from industry and 12% from commercial and residential buildings. Meanwhile, New Zealand has only 4.6 million people but 10 million cattle, so animal agriculture would naturally be a larger contributor of GHGEs in that country, where agriculture accounts for 47% of GHGEs.

“While trends in global averages of GHGE are important to monitor climate change, solutions need to be applied appropriately to individual countries and regions,” Layman writes.

Layman also points out that replacing animal protein with plant-based foods does not solve the problem of obesity. After all, most adults already consume more plant-based carbohydrates than required for energy balance, and these foods often consist of “processed grains with low nutritional value.”

Layman’s commentary provides the facts to help policymakers start making more informed decisions. The key is to consider the quantity and quality of food products we can produce before making drastic decisions about dietary recommendations or land use.

“Sustainable production of protein needs to be a foundation of a sustainable diet, and livestock have a critical role in production of high-quality protein,” writes Layman.