By Cat Holmes
University of Georgia
It all started with scientists taking a hard look at high- protein diets.
While the Atkins diet has fueled the debate about the safety of high-protein diets in humans, poultry scientists have known for years that when chickens are fed a high-protein diet, they produce less fat.
However, feeding chickens a higher-protein diet hasn't been commercially viable because protein is the most expensive part of chicken feed. Costlier feed would result in costlier chickens at the grocery store.
UGA poultry scientist Adam Davis decided to investigate the link between high-protein diets and leaner chickens and discovered a much more economical way to cut back on fat.
Fat happensBody fat in chickens is either derived from the diet or produced naturally by the bird. Like other birds, they're unique among animals in that they produce all of their fat in the liver. However, chickens aren't unique in where their fat is typically deposited: the abdominal area.
The diet-created fat is easy to control, Davis said, because "chickens today are typically fed a very low-fat diet that consists of about 22-percent protein."
But the fat that's created naturally, "just because," is harder to control. From both the producer and consumer standpoint, chicken fat is no good.
"From the farmers' standpoint, fat is a waste," Davis said. "Nobody wants to eat it, so you sure can't sell it."
Malic enzyme connectionDavis's first step was to investigate the action of malic enzyme, which is necessary for chickens to synthesize fat. If you reduce malic enzyme, he reasoned, the bird's ability to produce fat should be reduced. Indeed, his research bore this out.
Next, Adams did studies that showed that the reason high- protein diets result in leaner chickens is because they reduce malic enzyme activity.
Then, he decided to investigate whether a particular amino acid in protein was responsible for the reduction of malic enzyme. However, all amino acids tested out just fine.
"What we discovered is that anything with nitrogen had this effect," Davis said. "It wasn't any one amino acid doing it. They all do it."
Why nitrogen disrupts malic enzyme activity is still unknown, Davis said. What is known is that it happens very quickly.
"When chickens are fed nitrogen, the fat content of their livers is significantly decreased within 24 hours," he said.
Researchers are now investigating the best way to get that extra nitrogen in chicken feed. The challenge is to find a source that tastes good to chickens and is stable.
It looks like a small change in chickens' diet could literally make a big, fat difference.
(Cat Holmes was a science writer with the University of Georgia College of Agricultural and Environmental Sciences.)