Fat is a form of stored energy that is reserved to carry the body through periods when food is scarce.
More than 1 billion people worldwide are overweight, 300 million being obese (defined by body mass index).
Obesity increases the risk of diabetes, high blood pressure, heart disease, gallstones, arthritis, and cancer, thus increasing health care costs and shortening life expectancy. It also effects late life cognitive decline including Alzheimers and brain tissue loss. Memory and cognitive ability can be declined as well.
Fat has a lower metabolic rate than does muscle, it takes less food energy to maintain. When an overweight persons body drops below its previous set point, the persons hunger increases and metabolism decreases- the body adapts to starvation by burning off fewer calories.
Those who are lean are more active and burn more calories than overweight people.
Peoples weights resemble those of their biological parents. Identical twins have similar weights, even when separated. Genes explain 2/3 of our body mass.
People who suffer from sleep loss are more vulnerable to obesity. Levels of leptin (which reports body fat to the brain) fall, and gherkin (the appetite stimulating stomach hormone) rise.
Social influence is another factor- you're more likely to become obese when your friend becomes obese.
Our fattening world is the strongest evidence that environment influences weight. We eat more and move less.
Genes determine why one person today is heavier than another. Environment determines why people today are heavier than people 50 years ago.
A complex surveillance system. Keeps you healthy by isolating and destroying bacteria, viruses, and other invaders. Four types of cells are active in these search and destroy missions: B lymphocytes, T lymphocytes, macrophage, and natural killer cells.
Your age, nutrition, genetics, body, temperature, and stress all influence your immune systems activity.
When the immune system doesn't work properly, it can respond too strongly by attacking the body's own tissues causing arthritis or an allergic reaction. If it under reacts, dormant herpies or cancer can erupt.
Stress does not make us sick, but it does alter our immune functioning, which leaves us less able to resist infection.