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.
Water scarcity in Africa
Water scarcity or lack of safe drinking water is one of the world's leading problems affecting more than 1.1 billion people globally, meaning that one in every six people lacks access to safe drinking water. The Joint Monitoring Programme for Water Supply and Sanitation set up by the World Health Organization (WHO) and United Nations Children's Fund (UNICEF) defines safe drinking water as "water with microbial, chemical and physical characteristics that meets WHO guidelines or national standards on drinking water quality." Hydrologists generally assess water scarcity by looking at a population-to-water equation that treats 1,700 cubic meters per person as the national threshold for meeting water requirements for agricultural and industrial production, energy, and the environment. Availability below the threshold of 1,000 cubic meters represents a state of "water scarcity", while anything below 500 cubic meters represents a state of "absolute scarcity".