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Science is all about asking important questions.

Like: What does polar bear milk taste like? And the best way to find that out is… well… to taste it. So that’s exactly what polar bear scientist Andrew Derocher did. Turns out it’s got a creamy texture, and it’s a bit chalky, salty and even fishy.

And that reveals a lot about its composition, which gives researchers like Derocher insights into the lives of polar bears. Milk production is one of the defining features of mammals. That means all mammals, from platypus to humans, make some variety of the stuff.

Each species’ milk is tuned to the unique needs of their babies, so the composition—and resulting taste—can tell us a lot about that species. Of course, getting milk from a mother polar bear is no easy task, but intrepid researchers like Derocher have actually collected samples—and even tried them, just for good measure. Polar bear milk is pretty fishy tasting because it has lots of fishy-smelling oils, which come from the seal blubber mom is eating.

And it’s also salty or chalky because it has a lot of minerals, including sodium, in it. Saltiness is a common feature of marine mammal milks because sodium binds with other chemical compounds to help the cub absorb the fat and fat-soluble vitamins in the milk. And boy is there a lot of fat—that’s why it’s so creamy.

Analyses show that when the cubs are young, fat makes up about 40 percent of the mama bear’s milk, while another 11 percent is protein. Those hefty levels of fat and protein allow the cubs to drink relatively small amounts per day. A 50 kilogram, 8 month old cub only downs about 470 grams a day.

When our babies are that age, they’re only about 9 kilograms, yet they’ll drink around 750 grams a day. Mind you, human milk is much less rich. It has only a tenth of the fat of polar bear milk and a sixth of the protein.

So it’s much less creamy, but a lot sweeter, because it contains about seven times as much lactose or ‘milk sugar,’ which helps nurture the right intestinal microbes and boost baby’s immune system. Don’t look at me like that. You know you were wondering what human milk tastes like.

And while human milk isn’t quite as fatty as polar bear milk, it is fattier than cow’s milk. That’s because both human babies and polar bear cubs are born underdeveloped and helpless, or altricial, so they need a certain amount of fat and nutrients to finish their development outside the womb. The quicker that happens for the bears, the better, because that means less time when the young are vulnerable to predators or rivals.

Our species has family groups and tools to keep babies safe—polar bear mamas don’t. So they fast-track their cubs’ development by feeding them the bear version of half and half. The fact that mama bears produce such fatty milk is even more impressive when you realize that they produce it while starving.

In an extreme effort to keep their cubs safe, these moms hunker down with them in an underground snow den for 4 to 6 months. During that time the family never leaves, and mom has to slowly use up her own fat reserves to make the milk. And because those reserves are eventually limited, the milk actually changes flavor and becomes less creamy over time.

In addition to helping the cubs grow nice and rotund, that fat is also there as biological fuel. As you can imagine, it’s not exactly tropical inside a snow den. Cubs are born almost totally hairless, so they need a way to keep warm in those freezing temperatures.

A high metabolic rate allows their bodies act like mini furnaces and generate heat by burning some of the milk’s fat until they grow enough fur and fat to weather the cold. A lot of protein could also provide the needed caloric fuel, but it turns out protein is kind of troublesome for polar bears. Protein digestion creates waste products like urea or uric acid, which the body needs to dilute to make safe.

Despite all the ice around, there’s actually not that much drinkable water available to the bears, so if they eat too much protein, they can poison themselves. That’s why, if you look really closely at a nature documentary, you’ll see that polar bears munching on seals aren’t actually eating much of the meat. They’re going for blubber, because it contains a lot of fat and fluid.

Polar bear milk is also a little more sour at first because it contains more nutrients, immune cells and antibodies, which kick-start the newborns’ immune systems. And it contains a pretty hefty dose of vitamin D, which helps those little bear bodies absorb the calcium from the milk and grow strong bones. That’s important because polar bear cubs grow really fast so their bones need to be able to support all that new weight.

Vitamin D is sometimes called the sunshine vitamin because we can boost synthesis of it by going out in the sun—but since the baby bears are cooped up, they have to get theirs from mom. Unfortunately, those aren’t only things a mother bear passes along in her milk. Scientists are increasingly concerned that polar bear milk may be becoming bitter due to persistent pollutants.

Everything from flame retardants to pesticides is drifting up to the Arctic, and these chemicals, which can cause damage to the immune, digestive and reproductive systems of Arctic animals, collect in fatty tissues like blubber. So polar bears are particularly at risk because they eat so much contaminated fat. Bear moms then unknowingly pass these chemicals on to their cubs.

Scientists don’t yet know what impacts these pollutants have on cub growth or health but, needless to say, they might not be good. So they’re continuing monitor the levels of these contaminants and study their effects. And, strange as it may sound, further sampling of polar bear milk could help them keep an eye on that, as well tell them if there are any changes to the animals’ diet or overall health.

Who knew you could learn so much from a sip of milk? Thanks for watching this episode of SciShow! Every week we put out new episodes answering the most fascinating questions science allows us to ask.

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