Even when they are starving rattlesnakes grow, eating themselves from within to gain length while reducing girth.
This finding goes against previous reports that reptiles shrunk during lean times, as would be expected.
The western diamondback rattlesnake can go two years without food. Marshall McCue of the University of Arkansas studied 16 of the venomous creatures for 168 days, or more than five months.
Snakes starved for the entire period fed on their own stores, converting protein to carbohydrates. Calcium amounts doubled.
"Because it takes more energy to grow than to eat yourself, the snake changes shape by reducing its girth and putting its resources into skeletal muscles and bone," McCue said this week at a meeting of the American Physiological Society. "It isn't panicking."
The study supports a longstanding hypothesis that a snake's length correlates with physiological fitness, McCue said.
Fatty acids also increased as the snakes fasted. Over time, however, hydrogen was drawn from the fatty acids as an energy source.
McCue's work could point toward ways to manipulate human diets.
"We might be able to engineer diet so animals, and say humans in space, can tolerate food-deprivation better," he said.