‘Extraordinary’ Seal Milk May Redefine Baby Formula
Gray seal pups nurse on milk that is "extraordinary." (Getty/BjornStefanson)
Seal pups may be feeding on an unexpected biological treasure—one that could eventually influence human nutrition. According to a new study, milk produced by gray seals contains an unusually rich and diverse mix of sugars, far surpassing what has been identified in human breast milk.
Researchers found that gray seal milk contains about one-third more distinct sugar molecules than human milk, many of which have never been documented before. “The milk is extraordinary,” said Daniel Bojar of the University of Gothenburg in Sweden, lead author of the study published in Nature Communications.
Scientists say these newly discovered sugars could one day be added to infant formula to help strengthen babies’ immune systems, or even be used to support adult gut health. As milk scientists have long known, milk is more than just fat and protein—it also contains complex sugars known as oligosaccharides. These molecules play a critical role in early development by shaping gut bacteria, reinforcing the intestinal lining, and helping fend off harmful viruses and bacteria.
To conduct the study, researchers tracked five wild gray seals off the coast of Scotland throughout their entire 17-day nursing period. Milk samples were collected repeatedly and analyzed using mass spectrometry and artificial intelligence–based tools. The team discovered not only an unusually wide variety of sugars, but also changes in milk composition as the pups matured, a pattern similar to what occurs in humans.
In total, scientists identified 332 distinct sugar structures in gray seal milk, compared with about 250 known in human breast milk. Nearly two-thirds of the seal-milk sugars were previously unknown to science. Some were exceptionally large, forming chains of up to 28 sugar units—well beyond the 18-unit limit seen in human milk.
Laboratory tests on human immune cells showed that several of these seal-milk sugars can influence immune responses and demonstrate strong activity against disease-causing bacteria. The findings, researchers say, point to the vast and largely unexplored medical potential found in wild animals.
“The study highlights the untapped biomedical potential hidden in understudied wild species,” Bojar said.
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