Fasting like a king penguin

Most animals can survive difficult periods without food by drawing on their own body reserves. Fasting is a physiological ability of humans and animals with numerous therapeutic side effects. In nature, many places fast during the winter—periods when food is unavailable.

The king penguin holds the world record for living under the most extreme conditions: half a year in Antarctic temperatures as low as -40°C.

6-Month Fasting: Penguins and Physiology

The penguin pairs' eggs must be protected from the cold, while food must be brought in. One penguin seeks out distant hunting grounds, while the other stays and warms the egg.

King penguins have to fast up to 20 times every six months during their long lives – a total of 10 years!

The metabolism of fasting humans and penguins is very similar and well-studied. Due to its blood-brain barrier, the brain can only sustain itself on sugar or ketone bodies (products of fat breakdown).

During fasting, the metabolism adapts equally

First, the body begins to empty the sugar stores (so-called glycogen) in the liver and muscles and to convert a small amount of protein into sugar.

After a brief adaptation, the brain utilizes the ketone bodies produced from fat. Energy is generated almost exclusively through fat burning:

- In 24 hours, approximately 80 g of protein are broken down to be converted into sugar.
- The remaining energy requirement is covered by approximately 150 g of fat tissue.
- Protein breakdown for sugar production decreases (<3-5% of daily energy requirements).

A harmful limit is reached when approximately 35-45% of the total body protein has been broken down.

In normal-weight individuals, this occurs after approximately 40 days of fasting. In obese (severely overweight) individuals, fat reserves can sometimes last significantly longer.