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A New Meaning for Strip Steak: Making Red Meat Safer to Eat

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Posted October 9, 2019

Despite the rising popularity of plant-based burgers like the Impossible and Beyond, plenty of people still like the real deal.

Many studies have linked eating red meat (beef, pork, and lamb) to atherosclerosis, colorectal cancer, other ills, and shortened life. That’s why experts quickly challenged conclusions of a new study that downplayed the danger. I stopped eating red meat two years ago.

Now researchers have zeroed in on a single type of carbohydrate on the surfaces of the cells of red meat that might trigger the chronic inflammation that lies behind the associated illnesses. And they’ve found an intriguing way to remove it.

Food preparation. Image credit: pxhere.com, CC0 Public Domain

A Carb Culprit

In the past, the dangers of red meat have been blamed on salt, saturated fat, and even pollutants. Another culprit is a carbohydrate called Neu5Gc (short for N-glycolylneuraminic acid) that festoons the cells of nearly all mammals.

Thanks to a mutation that happened 2 to 3 million years ago, humans can’t make the enzyme that plucks Neu5Gc from the surfaces of cells from red meat. Nor can ferrets, platypuses, and certain dog breeds and monkey species.

Even though Neu5Gc isn’t on our cells, it gloms onto sugary carbs there. When circulating antibodies detect the meat-derived carbs, they trigger inflammation. Cancer cells are particularly deep in buried Neu5Gc.

Certain types of bacteria dine on Neu5Gc, extracting and using its carbon. And that gave Karsten Zengler, PhD, of the University of California, San Diego and colleagues the idea to look to the human gut microbiome to harness bacteria that could strip the carbohydrate from meat cells. They conducted a series of clever experiments that involved mice, microbiomes, and hunter-gatherers from Tanzania. Their findings appear in Nature Microbiology.

Experiment #1

The researchers modified mice to lack the gene that encodes the enzyme that breaks down Neu5Gc – a model of the human condition – and assigned them to one of three feeding groups: soy (with no Neu5Gc), pork (with lots of it), and edible birds’ nests (high in fiber). Compared to normal mice, the mutants developed three different, distinct gut microbiomes, depending upon which diet they followed.

(The microbiome is the collection of microorganisms living in a particular body part. The gut microbiome is analyzed from excrement, easy to obtain for an experiment.)

The mice that ate soy or birds’ nests developed much more diverse microbiomes than the rodents who ate pork. The meat-eaters had lots of the Bacteroidaies genus of bacteria that make an enzyme that breaks down Neu5Gc.

Experiment #2

The investigators had planned to track the gut microbiome in people as they switched from a vegetarian to a meat diet. But then they had a better idea.

Other investigators had already published gut microbiome data from 27 Hadza, an indigenous group living in grasslands around Lake Eyasi in the central Rift Valley of Tanzania. Their microbiomes are among the most diverse on the planet, reflecting the diversity of their diets as well as the absence of drugs such as antibiotics, and frequent exposure to cleaning agents like detergents.

The human microbiome. Image credit: NHGRI

The Hadza wander in groups of about 30 following food – they don’t grow anything. Their hunter-gatherer way of life is how humanity has fed itself for 95 percent of our existence. They have no leaders, only oral history, a unique tongue-click language, few possessions, and track time through the seasonal changes. The Hadza most closely resemble people who lived during the Paleolithic, from 2.6 million years ago until the dawn of agriculture about 12,000 years ago.

In the wet season, groups are small and scattered. During the dry season, Hadza men visit water holes for meat, from elephants, wildebeests, giraffes, and zebra. They also eat honey and berries. Women hang around the temporary camp and instead eat tubers (legumes, morning glories, various vines, squashes, melons and gourds).

The microbiomes of the women have adapted so well that enough nutrients are released from their fibrous foods to sustain pregnancies. Their gut microbiomes even include a species of Treponema, a relative of the bacterium that causes syphilis. These bacteria enable the Hadza to digest different types of fiber.

Notably, the gut microbiomes of the Hadza don’t include Bifidobacterium, the genus needed to digest milk that is also absent among vegans and Koreans. But they have the Bacteroidaies seen in the mice, which pump out the enzyme that strips Neu5Gc off of the cells of mammals like zebra and wildebeest. During the dry season, the Hadza make more than twice as much of the enzyme.

The researchers compared the Hadza gut microbiomes to those of 16 urban Italians and two rural groups from Burkina Faso and Malawi. As expected, the microbiomes of the Italians, who follow a Mediterranean diet, differed greatly from the Hadza, the two African groups not so much.

The Hadza gut microbiome has lots of Proteobacteria and Spirochaetes, which are almost non-existent among the urban Italians, who have abundant Actinobacteria that are nearly non-existent among the Hadza. More than a third of the bacterial genera in the Hadza microbiome hadn’t been seen before!

“The Hadza gut microbiome is likely an ‘old friend’ and stable arrangement fitting their traditional hunter-gatherer lifestyle,” the group concludes.

Experiment #3

The researchers synthesized the gene and the encoded enzyme in the lab, and the enzyme, as predicted, removes Neu5Gc from cell surfaces.

Experiment #4

The pièce de résistance was to sprinkle the lab-made enzyme onto pork sausage and steak. Off came the Neu5Gc!

“It’s our hope that this approach could be used as a probiotic or prebiotic to help reduce inflammation and the risk of inflammatory diseases — without giving up steak,” said Dr. Zengler. The group has filed a patent.

If a simple rub, like a meat tenderizer, can strip away the molecules on meat that provoke the inflammation behind the health risks, then the inventive new plant-based burgers may indeed have new competition.

Source: PLOS EveryONE

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