Health Tips from a Grizzly

Bear Hibernation

Story at-a-glance -

  • Hibernating animals are able to slow their metabolism almost to a point of suspended animation, and re-emerge after the inhospitable winter no worse for the wear
  • If a similar state (or mechanisms of it) was able to be induced in humans, it might have significant health ramifications for diabetes, heart disease, stroke and more

By Dr. Mercola

Hibernation is a survival mechanism that keeps certain animals alive through the winter months. Even when temperatures become freezing and food and water are scarce, hibernating animals barely notice as they slumber in a sedentary state.

But far from simply sleeping, hibernation involves multiple, sometimes counterintuitive, physiological shifts that give the animals a survival advantage. For instance, prior to hibernation animals will gorge themselves on food, becoming obese and, essentially, diabetic. During hibernation, animals’ lungs resemble asthmatics,’ with a thick coating of mucus and collagen.

Even hibernators’ brains show signs of changes akin to early-stage Alzheimer’s, and some lose their memories, yet come spring the animals emerge, seemingly unfazed. According to BBC News:1

As their body temperature drops, hibernators also remove the lymphocytes (white blood cells) from their blood and store them in the lymph nodes. And within 90 minutes of awakening, these reappear.

This damping down of the immune system prevents a general inflammation in the body during rewarming – the very thing that would cause humans and other non-hibernators to suffer kidney damage.”

Scientists Study Hibernation to Improve Human Health

That hibernating animals are able to slow their metabolism almost to a point of suspended animation, and re-emerge after the inhospitable winter no worse for the wear, has peaked scientists’ interest. If a similar state was able to be induced in humans, it might have significant health ramifications, including for the following diseases.2


When an arctic ground squirrel hibernates, the blood flow in its brain is just one-tenth of normal. The resulting oxygen deprivation would lead to a stroke in humans, but the squirrels survive because their metabolism also lowers to 2 percent of normal.

Thus, they require much less oxygen to survive. If we could lower metabolism similarly in humans having strokes, it might prevent brain damage from occurring. Rapidly cooling the body is one possibility for achieving this.


Grizzly bears gain 100-plus pounds prior to hibernation, yet, unlike humans their cells do not stop responding to insulin and they do not develop type 2 diabetes or other metabolic diseases. Research shows that bears’ fat cells actually change their response to insulin depending on the season.

They’re sensitive to insulin in the summer and fall, but during hibernation become insulin resistant (which is then reversed come spring).3 This insulin resistance helps them gain the fat they need to survive the winter.


When a black bear hibernates, its bone is recycled at 25 percent of its normal rate. This allows them to maintain their bone strength even after long periods of virtually no movement. Harnessing this ability in humans could have implications for those at risk of osteoporosis.

Heart Disease

Hibernating arctic ground squirrels prioritize the use of fat as fuel when they’re in low-oxygen conditions. This likely prevents the buildup of waste products, like lactic acid, which can be damaging to humans in an oxygen-deprived state (such as during heart surgery).

Researchers are looking into the artic squirrels’ ability to burn more fat than sugar during hibernation, as it could help reduce organ damage in humans undergoing surgery.

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Hibernating Animals Give Clues to Turning on Your Fat Switch

I highly recommend reading Dr. Richard Johnson's bookThe Fat Switch. In it, he reviews groundbreaking new research showing that eating too much and exercising too little are NOT solely responsible for why you keep gaining weight or have trouble shedding those excess pounds.

His research shows that metabolic syndrome (characterized by central obesity or increased waist circumference, high blood pressure and insulin resistance) is actually a normal condition that animals undergo to store fat.

Animals' ability to gain "hibernation fat" appears to be regulated by a switch in the mitochondria that is turned on and off by a common food that no longer provides survival advantage to humans living in contemporary society, namely fructose.

Fructose-containing sugars cause weight gain not by the calories they contain, but by triggering this "fat switch," which tells your body it's time to store fat, just as if you were an animal preparing for hibernation. According to Dr. Johnson:

“...most animals have learned how to become fat and how to become thin. They do it in a tightly regulated way... Hibernating mammals will double their weight and fat in the fall in preparation for winter...

These animals develop all the features of metabolic syndrome that we do. They get fat. They’re visceral fat goes up. They get fatty liver. The triglycerides go up in their blood. They get insulin-resistant... It’s a normal process.

It’s not a disease. This is how animals store fat. It’s part of the fat storage syndrome. I’ve actually proposed (and it’s in press) that the metabolic syndrome really should be called the fat-storage condition, because it’s just fat storage.”

The question, of course, is how do animals do it? Through his earlier research, Dr. Johnson discovered the method that animals use to gain fat prior to times of food scarcity, which turned out to be a powerful adaptive benefit. His research showed that fructose activates a key enzyme, fructokinase, which in turn activates another enzyme that causes cells to accumulate fat.

When this enzyme is blocked, fat cannot be stored in the cell. Interestingly, this is the exact same “switch” animals use to fatten up in the fall and to burn fat during the winter. Fructose is the dietary ingredient that turns on this “switch,” causing cells to accumulate fat, both in animals and in humans!

Human Mutations May Explain Why We Get Fat from Eating Fructose… But Other Animals Don’t

Dr. Johnson has also explained why humans seem to be especially sensitive to the effects of fructose, often becoming obese when exposed in excess (but without the ability to “switch back” to being thin, like animals do):

“'The enzyme that makes you fat is turned on in obese people,' Dr. Johnson explains, 'and the enzyme that makes you lean is turned off.' This is why the book is called The Fat Switch, because basically there is a switch that turns on and off. It looks to me like it’s universal to all animals.

This book is a story of that... [O]nce we realized that there was this switch, we asked, 'Why are people becoming obese?' Now we realized it was related to the sugar intake.

...The last part was connecting in with the evolutionary aspects. There’s a very famous evolutionary biologist in London, in the Natural History Museum. His name is Peter Andrews. He trained with Richard Leakey. He’s like a world expert on human evolution. It turned out that there were certain mutations that occurred in our past. For example, we don’t make vitamin C. We also have higher uric acids than most other animals.

When we look at when these mutations occurred, we could see that they actually occurred during periods of human famine, and that these were probably mutations that allowed us to become fatter in response to fructose than other animals. We’re much more sensitive to sugar than most animals, and it’s because of these mutations.

Then I was able to work with a spectacular scientist who helped resurrect those extinct genes. We’re able to basically prove that when we lost these genes, we became more sensitive to sugar. Then out of it comes the discovery that this pathway is probably important not just in obesity, but in a lot of other diseases like celiac disease, food allergies, and kidney disease.”

Effective treatment of insulin resistance and secondary obesity therefore requires turning off your fat switch – by avoiding fructose, which is the trigger – and improving the function of your cells' mitochondria. As a standard recommendation, I strongly advise keeping your TOTAL fructose consumption below 25 grams per day.  However, for most people – especially if you struggle with high blood pressure and insulin resistance – it would be wise to limit your fructose to 15 grams or less, as it is virtually guaranteed that you will consume "hidden" sources of fructose from most beverages and just about any processed food you might eat.

Is Your Body Primed for Hibernation?

Many people joke that they ‘hibernate’ through the winter. As the days get shorter and the weather gets colder, you might find yourself craving (and eating) high-calorie comfort foods and wishing you could spend the day curled up on your couch. Is this coincidence… or are humans primed for hibernation like other animals? There are stories of humans hibernating. One such story was published in the British Medical Journal in 1900, and told of a group of Russian peasants who were in a state of chronic famine. When winter approached, they would stay indoors and wake just once a day to eat bread and drink water, and take turns watching the fire, before falling back into a deep slumber.4

Many animals, including mammals, birds, fish, insects and amphibians, have the ability to slow their metabolism and enter low-energy states for survival (this is known as torpor). This is how mice, hamsters and bats survive the winter; they have regular bouts of torpor. It’s also possible that humans might have some remnants of torpor. BBC News explained:5

“There are even hints that we humans might, to some extent, retain some of these abilities. For a long time, there was no evidence that primates could hibernate. But in 2004, a species of Madagascan lemur was shown to practice regular bouts of torpor. 'If you look at the lemur and look at us, we share about 98% of our genes,' says [professor Rob] Henning. 'It would be very strange if the tools of hibernation were all packed into that 2% difference.'”

There has even been suggestion that people with seasonal affective disorder (SAD) (a type of depression that occurs during the winter) might have “hibernation-like physiology.” For instance, prior to hibernation, animals have a spike in their parasympathetic nervous system, which slows their heart and metabolic rate and lowers body temperature. Researchers have discovered a similar spike in people with SAD.6 Rather than hibernating through winter, however, as some animals do, humans may respond to their hibernation-like physiology by eating more, gaining weight and sleeping more than usual.

Do You Need Help Fighting Off Winter Hibernation?

If the short days and long nights of winter leave you feeling fatigued, craving sugary and starch foods, and like you’d rather just “hibernate” until spring, try getting exposure to sunlight as much as possible. Vitamin D deficiency has long been associated with Seasonal Affective Disorder, so spend time in the sun when possible or use a high-quality tanning bed. Blue light therapy and using full-spectrum lighting in your home and office can also help. You can further boost your mood naturally during the dark, cold winter by:

  1. Exercising. Regular physical activity works as well as antidepressant drugs to improve your mood. In fact, it’s one of the most powerful strategies you can take to prevent and treat depression and boost your mood.
  2. Going to sleep early. You were designed to go to sleep when the sun sets and wake up when the sun rises. If you stray too far from this biological pattern you will disrupt delicate hormonal cycles in your body. In the winter, this may mean that you’ll want to go to sleep a couple of hours earlier than in the summer.
  3. Avoiding sugar/fructose and increasing high quality animal-based omega-3 fats. Your brain consists of about 60 percent fat, DHA specifically, so you need a constant input of essential omega-3 fats like krill oil for your brain to work properly. In fact, one study showed that people with lower blood levels of omega-3s were more likely to have symptoms of depression and a more negative outlook while those with higher blood levels demonstrated the opposite emotional states. Sugar (including fructose) also has a seriously detrimental impact on your brain function and may turn on your body’s “fat switch.”