Research shows that obesity results in brain degeneration. Those classified as overweight have 4 percent less brain tissue and their brains appear to have aged prematurely by 8 years. For obese people, a new study finds that they have 8 percent less brain tissue than normal-weight individuals. Their brains look 16 years older than the brains of lean individuals.

Large scale American and European studies have found that mortality risk varies with BMI; the lowest risk is found at a BMI of 22.5–25 kg/m2. A BMI of over 32 has been associated with a doubled mortality rate among women over a 16-year period. A BMI of 30–35 reduces life expectancy by two to four years while severe obesity (BMI > 40) reduces life expectancy by 20 years. Obesity on average reduces life expectancy by six to seven years. Obesity is one of the leading preventable causes of death worldwide. Every year in the United States, obesity is estimated to cause 365,000 deaths.

Sturm and Wells examined data from Healthcare for Communities, a national household telephone survey fielded in 1998. Approximately 10,000 respondents participated in the survey, which was designed to be nationally representative. The study reveals that obesity is linked to very high rates of chronic illnesses — higher than living in poverty, and much higher than smoking or drinking. Figure 2 compares the increase in chronic conditions related to obesity. When compared with normal-weight individuals of the same age and sex having similar social demographics, obese people suffer from an increase in chronic conditions of approximately 67 percent. In contrast, the increase for normal-weight daily smokers is only 25 percent; and for normal-weight heavy drinkers, only 12 percent.