For a long time, researchers would use rats when it came to determining the digestibility of certain proteins in humans.
That was old news to Hans Stein.
For 30 years, the University of Illinois animal scientist had been evaluating nutrient digestibility in pigs and how that relates to the ability of humans to digest the same proteins.
“When it comes to nutrition, pigs are the best model,” Stein says.
He was among many researchers who helped develop a new index known as the digestible indispensable amino acid score (DIAAS). It rates the digestibility of individual amino acids making up proteins.
Stein and his colleagues published the first paper on DIAAS in 2014. Multiple studies have since followed.
“The FAO determined the pig is the preferred model for humans when you evaluate proteins, moving away from the rat, which had been used for the last hundred years,” he says. “They also recommended human foods should be evaluated exactly the same way as we evaluate feed ingredients for pigs.”
In a new study published in the British Journal of Nutrition, Stein and his co-authors demonstrate how meat products such as ribeye steaks, bologna and beef jerky score higher than 100 on the DIAAS chart. Stein says this means their amino acids are highly digestible and complement lower-quality proteins.
“If the protein quality is greater than 100, that means it can compensate for low protein quality in another food,” he says. “In developing countries where people are eating a lot of maize or rice, they are typically undernourished in terms of amino acids. But if they can combine that with a higher-quality protein such as a small amount of meat, then you have improved quality overall.”
In the study, nine pigs were fed each of nine meat products for a week. Those included salami, bologna, beef jerky, raw ground beef, cooked ground beef, and ribeye roast cooked medium-rare, medium, and well-done.
Researchers collected material from the pig’s ileum, part of the small intestine, through a small surgically placed port called a cannula. Amino acid digestibility and DIAAS were calculated for various human age groups using this material.
Stein says meat preparation can affect proteins, so it was vital that the pigs ate the same form of meats that humans consume.
“We did feed ribeye steaks to the pigs,” Stein says. “They loved it.”
He says nearly all of the DIAAS values were over 100 regardless of processing for all the meat products and age groups.
“The reason for that is the amino acid requirement, and the requirement for higher quality protein, is greater for younger children because they’re actively growing,” Stein says. “Adults don't necessarily need a very high protein quality because their protein needs are not very high, unless they are bodybuilders or nursing women.”
Among the meat products tested, bologna and medium-cooked ribeye steaks had the highest DIAAS values for older children, adolescents and adults.
Stein adds earlier research indicates milk and other dairy products are great protein sources for children.
In the future, he will evaluate fish, eggs, plant-based meats and other products.
“We are one of the few labs doing this work, and we are doing quite a bit of it,” he says. “It’s very important work, especially for developing countries that need animal protein to supplement their diet.”