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.
Perennial water
Perennial water body usually refers to mainly liquid fresh water, as opposed to sea and glaciers or other ice. Most frequently the term refers to running water (lotic ecosystems) as in perennial streams and large rivers, but the distinction between perennial and non-perennial water is of equal importance in lentic aquatic ecosystems, those that are associated with relatively still terrestrial waters such as lakes and ponds. Simplistically a perennial water body is one that keeps full or flowing throughout the year for all or most years, but in practice there are degrees and kinds of distinction. The definition is not precise, because most water bodies vary in fullness according to the season, and according to the heaviness of precipitation and other factors during any given year. Also, the water level in many such water bodies as do not actually dry out, may nonetheless drop so drastically that their surface area is greatly reduced. They even may be split into several separate water bodies with dry land between, either arid or covered with vegetation. The internal ecology of such water may differ drastically between periods of drought and deep water. In some cases the seasonal cycle is ecologically important, whereas in other examples exceptional water levels are too rare to be taken routinely into account. There also may be effectively permanent changes; increasingly frequently even large rivers have lost their perennial status under the burden of the human demand for fresh water for purposes of agriculture, industry or the needs of the populations of large cities. The Colorado River for instance has run dry for extended periods in most years since 1960 without reaching the sea. Intermittent or ephemeral streams are those that run dry repeatedly, either seasonally or soon after rain stops. Some definitions of perennial water bodies specifically include those that only are perennial except in years of severe or unusual drought.