Missing gut microbes linked to childhood malnutrition

In children suffering from malnutrition, the right mix of microbes might be what’s missing.

The bacteria living in kids’ guts play a starring role in growth and development, three new studies published February 18 in Science and Cell suggest.

Food matters, too, but not as much as people once thought, says biologist Brett Finlay of the University of British Columbia, who was not involved in the new work. “People used to think if you just fed the kids they’d be fine,” Finlay says. “But that didn’t work.” Instead, certain gut microbes might be needed to protect children suffering from poor diets. “It’s extremely exciting,” he says. “We know what causes malnutrition, and maybe now we can do something to fix it.”

Each year, malnutrition contributes to the deaths of more than a million children worldwide. Millions others survive, but a lack of calories or nutrients can stunt growth, delay brain development and harm the immune system. Even after they receive adequate food, many of these kids just don’t bounce back, Finlay says. “Everyone’s been kind of puzzled about why.”

In recent years, scientists have seen several hints that microbes might have something to do with it. But no one knew if microbes could actually treat malnutrition, and if so, which strains of bacteria would help.

Biologist François Leulier and colleagues report in Science that they discovered the helpfulness of one microbe, Lactobacillus plantarum strain WJL. The team fed two types of infant mice — either with or without gut bacteria — a low-protein diet until young adulthood and measured the mice’s development. “We started to see these amazing features in juvenile growth,” says Leulier, of the Institute of Functional Genomics of Lyon in France. “The germ-free animals are stunted completely.” Mice with microbes, on the other hand, were bigger all around: bones, organs and body size, too. Gut microbes give mice the green light to grow by cranking up production of a growth hormone called IGF-1, the team discovered. Just one strain of L. plantarum can do the job.

The strain’s growth-boosting effects, even in the face of a poor diet, give Leulier hope for treating malnutrition — though that day is still a long way off.  “We can envision some therapy solutions,” he says, “but we’re still at the basic research level.”

A study of young Malawian children turned up more potentially helpful microbes, says physician and microbiologist Jeffrey Gordon of Washington University in St. Louis. He and colleagues analyzed gut bacteria of healthy and malnourished babies. Kids of similar ages typically share similar sets of bacteria, Gordon has found. But malnourished Malawian babies had a microbial mix that resembled that of even younger babies, the team reports in Science. In 2014, Gordon’s team reported similar “immature microbiomes” in malnourished Bangladeshi kids (SN Online: 6/4/14). These stunted microbiomes may be a universal red flag for poor nutrition. And they could be part of what’s making malnourished kids so sick.

Mice that receive these kids’ microbes don’t grow as well as mice that get microbes from healthy kids. But giving the runty mice two additional bacterial species, Ruminococcus gnavus and Clostridium symbiosum, can solve the problem, the researchers discovered: The mice begin to grow again.

Like the work of Leulier’s team, Gordon’s findings hint at a potential treatment for malnutrition.

“It’s the first step in the journey,” he says. His team wants to find foods that nourish healthy microbiomes.

Gordon’s team has already had some success. In a separate study, they analyzed breast milk of Malawian mothers who had either healthy or stunted infants. Mothers with healthy babies had breast milk full of carbohydrates that contained a chemical called sialic acid, the team reports in Cell. These carbs could be key for growth.

But it’s not easy to get enough human breast milk to manufacture large quantities of these carbohydrates, Gordon says, so the researchers turned to a cheese company in California. They purified structurally similar carbohydrates from whey, a by-product of making cheese from cow milk. Cow carbs boosted growth of mice and piglets with bad gut microbes, the team found.

Taken together, the new studies underscore microbes’ contribution to human development, Gordon says.

Finlay agrees. “We know microbes play a major role in obesity, but this really confirms their role in malnutrition,” he says.