A Long Winter’s Nap :Oxidizing Fats during Hibernation

In summary, In hibernating animals, fatty acid oxidation provides metabolic energy, heat, and water all essential for survival of an animal that neither eats nor drinks during hibernation

Hibernation Facts

Grizzly bears can hibernate for up to seven months

maintaining a body temperature of around 31°C, which is only slightly lower than their normal temperature of 40°C.

Metabolic Adjustments

- Energy Expenditure: They burn about 25,000 kJ/day (or 6,000 kcal/day) without eating, drinking, urinating, or defecating.

- Heart Rate: Drops from 90 beats per minute to 8 beats per minute.

- Respiration Rate: Slows from 6-10 breaths per minute to around 1 breath per minute.

• Glycerol from fat breakdown is converted into glucose through gluconeogenesis.

• Urea formed during amino acid breakdown is recycled by the kidneys, helping to produce new proteins and preserve muscle mass.

Thermoregulation

Grizzly bears can uncouple mitochondrial electron transfer from ATP production, allowing energy from fuel oxidation to be released as heat to maintain body temperature in cold environments.

- Brown Adipose Tissue: This specialized fat tissue is essential for heat generation (thermogenesis).

Preperation for hibernation

-Bears eat heavily—up to 84,000 kJ/day in late fall storing large amounts of fat from carbohydrates.

-They can lose 15-40% of their body weight by the time they wake up.

Hibernation vs. torpor

• Unlike bears, smaller animals like Arctic ground squirrels experience true hibernation:

  • Their body temperature drops close to 0°C, and metabolism slows significantly.

  • They have brief wakeful periods to eat and drink.

• Torpor - winter sleep of bears