Autophagy, self eating, – it’s actually a thing.
All animals have to deal with food lack to some extent, because of changing food resources, or migration. The bar-tailed godwit, an arctic bird, can go for more than a week and fly 6000 miles without eating. (1)
One way to deal with lack of food is by slowing metabolism to burn fewer calories – hibernation. The black bear can hibernate for 5 months without eating and can convert urea in their urine to proteins to reduce muscle loss. Obviously olympically migrating birds are not hibernating but another way to survive food deprivation is to eat yourself for a while. That’s more than just burning fat stores. This ‘self-eating’ process to provide energy when nutrients are scarce also rids the cell of intracellular misfolded proteins or damaged organelles and can rejuvenate organs. Autophagy may make periods of fasting beneficial. Though depending on fat stores, most animals, including humans, can only go for a few months without eating.
Some eels however, can shrink by more than 50% and go for 4 years without eating. So they represent a good candidate for studying the genes and the action of those genes for autophagy. (2) Like salmon, eels can migrate from saltwater in the oceans into fresh water rivers. In eels the response to autophagy also controls their sex. Eel sex is not determined by chromosomes or manifest at birth. Another reason to study eels is that despite their amazing powers of self preservation, many species are going extinct. They have a panel of autophagy-related genes (atg) for maintenance and control of self eating during periods of fasting. Many of these genes are also widely found in the animal kingdom and even in yeast where they were first studied.
Understanding the dynamics and control of autophagy may offer a back door to weight loss in the treatment of obesity and also a way to increases longevity without hunger. But in the meantime there’s no substitute to avoid the pain of fasting, something we probably had to do often in the past but never do anymore. I wonder if Muslims who practice periodic fasting during the month of Ramadan live longer.
1. Stone D. Animal appetites. National Geographic 2014(May)p24.
2. Bolliet V, et al. Modeling of autophagy-related gene expression dynamics during long term fasting in European eel (Anguilla anguilla). Scientific Reports 7, Article no: 17896 (December, 2017)