Maintaining a healthy diet is the practice of making choices about what to eat with the intent of improving or maintaining good health. Usually this involves consuming necessary nutrients by eating the appropriate amounts from all of the food groups, including an adequate amount of water. Since human nutrition is complex, a healthy diet may vary widely, subject to an individual's genetic makeup, environment, and health. For around 20% of the planet's population, lack of food and malnutrition are the main impediments to healthy eating; people in developed countries have the opposite problem, and are more concerned about obesity.