An alarming decrease in exercise rates may be to blame for an increase in obesity, Stanford research shows. It sounds like a good cover story after you load up at the dessert buffet: \u201cFor the record, I don\u2019t overeat, I under-exercise.\u201d But Stanford University Medical School researchers are reporting that a steep drop in physical activity rather than caloric intake may explain the country\u2019s mounting obesity rate. The Stanford researchers reported that the percentage of women reporting no physical activity jumped from 19 percent to 52 percent between 1988 and 2010; the percentage of inactive men rose from 11 percent to 43 percent over the same period. Obesity also increased, climbing from 25 percent to 35 percent in women and from 20 percent to 35 percent in men. This dramatic rise in the level of inactivity since 1988, without a significant jump in calories over the same period, has led the Stanford research team to conclude that output of energy versus intake of food could be to blame for the obesity epidemic. The findings are based on national health survey responses. RELATED: Role of Addiction in the Obesity Epidemic \u201cWhat struck us the most was just how dramatic the change in leisure time physical activity was,\u201d\u00a0Uri Ladabaum, MD, lead author of the study and a Stanford associate professor of gastroenterology, said in the university\u2019s news announcement. \u201cAlthough we cannot draw conclusions about cause and effect from our study, our findings support the notion that exercise and physical activity are important determinants of the trends in obesity.\u201d The potential impact of these findings is hard to overstate. More than one in three people in the U.S. is obese. That\u2019s according the latest reports by the federal Centers for Disease Control and Prevention. Child obesity in the U.S. has declined some, although the World Health Organization in May 2014 reported that 25 percent of children and adolescents globally are obese, and labeled the increase \u201cepidemic.\u201d (The findings pertain only to the one-third of the population that is obese versus overweight. You can input your height and weight and find out the difference at the CDC\u2019s website.) While health advocates have long urged Americans to exercise, the consumption of high levels of fats, calories and sugar has primarily shouldered the blame for obesity. In the Stanford research study, which will be published in the August issue of\u00a0The American Journal of Medicine, the team evaluated national health survey results from 1988 through 2010; what the team called \u201chuge increases in both obesity and inactivity\u201d were discovered -- but not a notable spike in calories consumed. Led by Ladabaum, the team analyzed data from the National Health and Nutrition Examination Survey, a long-term project of the CDC; the CDC gathers data from physical exams of Americans as well as surveys to reach results. The researchers considered survey results from 17,430 participants from 1988 through 1994 and from about 5,000 participants each year from 1995 through 2010. Survey participants recorded the frequency, duration and intensity of their exercise within the previous month, Stanford\u2019s news announcement stated. The team defined "ideal" exercise as more than 150 minutes a week of moderate exercise or more than 75 minutes a week of vigorous exercise.