The BEAR Necessities of Life: 4 Lessons for Restoring Insulin Sensitivity

Humans are like bears

Bears and humans share a commonality in their metabolic response to high sugar intake.[1] Yet their outcomes diverge significantly due to evolutionary adaptations and lifestyle differences. Bears exhibit a natural, reversible insulin resistance cycle tied to their hibernation, enabling them to store fat efficiently and survive months without food[2]. In contrast, humans who overconsume sugars and starches often develop chronic insulin resistance, a precursor to type 2 diabetes. We will explore the bear’s adaptive insulin resistance cycle and compare it to human metabolic dysfunction. We can learn from the metabolic cycling of a grizzly bear how to manage our own metabolism and restore insulin sensitivity.

The Bear’s Adaptive Insulin Resistance Cycle[3]

Bears, such as black bears (Ursus americanus) and grizzly bears (Ursus arctos), have evolved a remarkable metabolic strategy to survive harsh winters. This cycle can be broken down into distinct phases:

1. Hyperphagia (Late Summer to Early Fall)

In preparation for hibernation, bears enter hyperphagia, a period of intense feeding. They consume up to 20,000 calories daily, often from sugar-rich foods like berries, which are high in fructose and glucose. This triggers a spike in blood glucose, stimulating insulin release. Insulin facilitates glucose uptake and promotes fat storage by converting excess sugars into triglycerides. During this phase, bears develop insulin resistance, particularly in peripheral tissues like muscles, to prioritize fat synthesis over immediate energy use. They become less active.

A 2018 study on grizzly bears found that this insulin resistance is regulated by hormonal changes, including elevated cortisol and reduced insulin signaling, ensuring calories are stored as fat, increasing body weight by up to 40%. A grizzly bear may increase 150 pounds of fat in the late summer and fall. As they get fat, they have less energy because of insulin resistance. They get tired. They want to sleep, so they find a cave, or build a nest and go to sleep.

2. Hibernation (Winter)

During hibernation, bears enter a state of torpor lasting 5-7 months. Their metabolic rate drops to 25% of normal, heart rate slows from 80 to 10-20 beats per minute, and body temperature decreases by 7-12°F. They rely entirely on fat reserves, burning approximately 4,000-6,000 calories daily and losing 15-30% of body weight.

How does the bear survive without any food or water for six months or more? Fat metabolism produces water, and they don’t urinate at all, recycling their water. Also, for every pound of fat burned, a pint of water is produced, preventing dehydration from evaporative losses. The bear also prevents the loss of protein by urea recycling (making amino acids from nitrogenous waste products) minimizing muscle loss[4]. As glucose levels stabilize because fat is metabolized, insulin sensitivity is gradually restored, preparing bears for spring.

3. Spring Awakening

Emerging from hibernation, bears are leaner and insulin-sensitive. Their early spring diet includes protein-rich foods like carrion and insects, supporting muscle rebuilding. As the season progresses, they transition to mixed diets before returning to sugar-rich berries in late summer, restarting the cycle. This metabolic flexibility, documented in a 2014 study on black bears, prevents chronic metabolic disorders and ensures survival.[5] As they eat the sugar-rich berries in the late summer, they become insulin resistant, gain weight, get lethargic, and go back to sleep and fast for six months, repeating the cycle every year.

Human Overeating and Chronic Insulin Resistance

Humans have a similar metabolism. The problems seem to be that because of the abundance of “ripe berries” with the sugar that we, like bears, love so much, we are continually in hyperphagia. Overconsumption of sugars (e.g., sucrose, high-fructose corn syrup) and refined starches (e.g., white bread, pasta) mimics aspects of a bear’s hyperphagia but lacks the adaptive resolution, meaning we don’t fast for six months to use it up. Here’s how it unfolds:

1. Chronic High Sugar and Starch Intake

Frequent consumption of carbohydrates leads to repeated blood glucose spikes, triggering excessive insulin release. Over time, cells, particularly in muscle and fat tissue, become less responsive to insulin, leading to insulin resistance. This forces the pancreas to produce more insulin, creating a vicious cycle. Higher insulin causes lower energy so people use caffeine, stimulants and sugar to increase the adrenal hormones (cortisol, adrenaline) to feel like they have more energy. These hormones cause more insulin resistance and make the problem worse, ending in type 2 diabetes. Unlike bears, humans often maintain this high intake year-round, with no equivalent to hibernation to reset metabolism. A 2020 study in The British Medical Journal[6] linked prolonged high sugar intake to visceral fat accumulation and a 30-40% increased risk of type 2 diabetes.

2. Consequences of Insulin Resistance

I have many people wonder why they are active and not eating very much, but they continue to gain weight and feel fatigued. Chronic insulin resistance in humans leads to elevated blood glucose, promoting fat storage, particularly in the liver and abdomen, which exacerbates metabolic dysfunction. This can progress to type 2 diabetes, cardiovascular disease, and other comorbidities. Unlike bears, humans lack a natural fasting period to burn fat reserves, and sedentary lifestyles compound the issue by reducing glucose uptake in muscles. Fatigue sets in. There is not enough energy in the muscles because it’s all getting stored as fat.

3. Absence of a Natural Reset

Bears benefit from a prolonged fasting state during hibernation, which depletes fat stores and restores insulin sensitivity. Humans, however, rarely experience extended periods without calorie intake in modern diets, leading to persistent insulin resistance. The constant availability of food disrupts the metabolic flexibility seen in bears.

Lessons from Bears: Periodic Carbohydrate Restriction

The bear’s cycle suggests that humans could improve insulin sensitivity by mimicking aspects of this natural rhythm through periodic reduction of sugar and starch intake. Here’s how:

1. Intermittent Fasting or Low-Carb Periods

Intermittent fasting or low-carbohydrate diets (e.g., ketogenic or paleo) can simulate the fat-burning phase of hibernation. By reducing sugar and starch intake, blood glucose and insulin levels drop, allowing the body to tap into fat reserves for energy. A 2019 study in Cell Metabolism found that a low-carb diet for 8 weeks improved insulin sensitivity by 20-30% in prediabetic individuals[7].

2. Benefits of Restoring Insulin Sensitivity

Periodic carbohydrate restriction can:

• Reduce Fat: Lower insulin levels promote lipolysis, burning visceral fat similar to a bear’s hibernation. The body needs to burn 60% fat to have energy, this is how the bear wakes up in the spring – eating carrion and fish.
• Improve Energy: Improved insulin sensitivity allows your muscles to use glucose more efficiently, reducing blood sugar spikes.
• Improve Mental Clarity: The brain is especially sensitive to insulin resistance since it relies mostly on glucose.
• Prevent Chronic Disease: Studies show that cycling between low-carb and moderate-carb diets can lower HbA1c levels and reduce type 2 diabetes, cardiovascular disease, and cancer risk[8].

3. Practical Implementation

To adopt a bear-inspired approach, humans can:

• Cycle Carbohydrate Intake: Alternate between periods of low-carb eating (e.g., 20-50g carbs/day for 1-2 weeks) and moderate-carb periods (100-150g/day), mimicking the bear’s seasonal shifts.
• Prioritize Whole Foods: Replace processed sugars and starches with nutrient-dense foods like vegetables, lean proteins, and healthy fats, akin to a bear’s varied spring diet.
• Incorporate Fasting: Practice intermittent fasting or time-restricted eating to induce fat-burning states, similar to hibernation. Fasting is the single best way to enhance metabolic flexibility[9]. Just like a bear, you could fast for long periods of time, but that is not necessary. Some people fast for 5 days 3-4 times per year, as recommended by Dr. Valter Longo[10]. His program is called “fasting mimicking” because it allows food to be eaten. Others, eat breakfast and lunch, and skip dinner, (It is better to skip dinner than to skip breakfast.) fasting for 16-18 hours daily. Some eat only breakfast every day. Others eat three meals every other day. The more you have an empty stomach, the better for your health… but you must eat sometime!

Personally, I have found that fasting for 72-hours every month is the best. It allows me to be flexible on the days that I eat, and every month I clear out all the excess carbs and fat that build up, allowing me to switch from glucose to fat in a moment so I never get low energy. It takes about 2 days to use up your stored glucose and induce ketosis from burning fat. So, I get one day in ketosis every month. It works!

4. Considerations

Bears are naturally very active when awake. Humans must balance dietary changes with exercise, to further enhance insulin sensitivity.

• Humans don’t recycle proteins as much, so we need to exercise during fasting to prevent muscle loss.
• We don’t recycle water, so we need to keep hydrated. It is good to drink water with a pinch of salt in it for electrolyte balance. (Avoid sweetened electrolyte drinks or powders.) There is no specific amount, as that will depend on how much you sweat, and so forth. It’s good to drink if you’re thirsty.
• After fasting for more than 48 hours it is good to start eating foods with fiber such as vegetables, beans, lentils, salads, and mushrooms. Avoid the sweet fruit at first, as it will increase insulin rapidly.

Conclusion

The bear’s insulin resistance cycle is a masterclass in metabolic adaptation, allowing them to store fat efficiently and reset insulin sensitivity through fasting. Humans, by contrast, face chronic insulin resistance from the sustained overeating of sugars and starches, lacking a natural reset. By adopting periodic carbohydrate restrictions, humans can mimic the bear’s fasting phase, burning fat and restoring insulin sensitivity. This approach, supported by emerging research, offers a practical strategy to combat metabolic dysfunction and promote long-term health. Embracing nature’s lessons could help humans achieve the metabolic flexibility that bears have perfected over millennia.

References

[1] iScience. Volume 25, Issue 10105084 October 21, 2022; Serum plays an important role in reprogramming the seasonal transcriptional profile of brown bear adipocytes; Michael W. Saxton1,

[2] J Comp Physiol B. 2017 May;187(4):649-676. doi: 10.1007/s00360-016-1050-9. Epub 2016 Dec 16.

Life in the fat lane: seasonal regulation of insulin sensitivity, food intake, and adipose biology in brown bears

K S Rigano et. al.

[3] Clin Transl Sci. 2015 Jun 17;8(5):601–605. Insights from the Den: How Hibernating Bears May Help Us Understand and Treat Human Disease; Maria Berg von Linde 1,✉, Lilith Arevström 1, Ole Fröbert 1

[4] https://www.kidney-international.org/article/S0085-2538(15)55736-0/pdf

[5] Annual Review of Cell and Developmental Biology Volume 36, 2020; Cellular, Molecular, and Physiological Adaptations of Hibernation: The Solution to Environmental Challenges; Sarah M. Mohr, et. al.

[6] BMJ. 2018 Nov 14:363:k4583. doi: 10.1136/bmj.k4583. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial; Cara B Ebbeling et. al.

[7] J Clin Invest. 2021 Jan 4;131(1); Dietary interventions for obesity: clinical and mechanistic findings

Ariana M Chao 1, et. al.

[8] J Clin Invest. 2021 Jan 4;131(1); Dietary interventions for obesity: clinical and mechanistic findings

Ariana M Chao 1, et. al.

[9] https://scientificorigin.com/metabolic-flexibility-how-to-train-your-body-to-burn-fat-and-sugar

[10] https://valterlongo.com/fasting-mimicking-program-and-longevity/