A study published in Aug 2011 in the Journal of Adolescent Health found that being overweight at 25 years old increased the risk of early death by 21%. That risk went up to 28% if a young adult with a higher BMI (body mass index) also smoked, drank alcohol, or did little exercise.
The risk of early death was higher in obese men compared to women, and African-American women compared to white women.
They found that in all ethnic groups, except in African- American men, the shortened lifespan risk due to being overweight in young adulthood is not cancelled out by later weight loss in middle age.
They conclude that a healthy lifestyle must be established and maintained from an early age.