Leopard gecko tails are used to store fat; they can use this reserve in times of famine when food sources are sparse. (petco.com)
Marshmallow root has long been used as a food, particularly during times of famine when it is more abundant than other vegetables. (wellnessmama.com)
Blame it on evolution: Your body doesn't want to lose weight, so it becomes efficient at doing more with fewer calories when faced with times of famine, which in these modern times is called a diet. (scientificamerican.com)