Almost one-third of all American adults are obese, and the number could rise to almost 40 percent within five years, according to a leading obesity researchers.

James Hill, director of the Center for Human Nutrition at the University of Colorado Health Sciences Center, said 59 million Americans fit the definition of obese, which is roughly 30 or more pounds over a healthy weight.

He said another 34 percent of American adults are overweight, which is approximately 10 to 30 pounds over a healthy weight.

Americans are gaining one to two pounds a year, Hill said in an article in the journal Science. To stop this weight gain, he said people need to either consume 100 fewer calories daily or burn an additional 100 calories with increased physical activity.

Other sources: Science