Human
In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days. About 36 million humans die every year from causes directly or indirectly related to starvation. Childhood malnutrition is also common and contributes to the global burden of disease. However global food distribution is not even, and obesity among some human populations has increased rapidly, leading to health complications and increased mortality in some developed, and a few developing countries. Worldwide over one billion people are obese, while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic." Obesity is caused by consuming more calories than are expended, so excessive weight gain is usually caused by an energy-dense diet.
Apnea
When a person is immersed in water, physiological changes due to the mammalian diving reflex enable somewhat longer tolerance of apnea even in untrained persons. Tolerance can in addition be trained. The ancient technique of free-diving requires breath-holding, and world-class free-divers can hold their breath underwater up to depths of 214 metres and for more than four minutes. Apneists, in this context, are people who can hold their breath for a long time.