A drastic decline in the amount of exercise people are engaging in, rather than diet and overeating, is the primary factor behind an increasingly worrying obesity epidemic, according to new research. We often hear that a diet high in saturated fat and/or high in sugar is to blame for weight gain, but it seems it could be purely down the fact we are not moving about enough, and lifestyles have simply become too sedentary. It is recommended that adults aged between 19 and 64 engage in at least 150 minutes of moderate-intensity exercise each week, which can include activities such as brisk walking, cycling, gardening, etc., in addition to at least two days which includes some form of muscle strengthening exercise. However, research has shown that around two in three adults in the UK are failing to hit this target, with two thirds of men and nearly six in 10 women being either overweight or obese. Only Iceland and Malta can lay claim to having a higher number of overweight or obese people in Western Europe. And now a new US study discovered that over the last 22 years there has been a sharp drop in the amount of time Americans spent exercising whilst not at work, with a correlating increase in average body mass index (BMI). Perhaps interestingly, the researchers at Stanford University School of Medicine could find no clear evidence that American's have increased their daily calorie intake during this same time period – suggesting lack of exercise is behind an obesity epidemic causing huge problems and thousands of deaths at both sides of the Atlantic. “We wouldn't say that calories don't count, but the main takeaway is that we have to look very carefully at physical activity. The problem is not all in the intake of calories,” said Dr Uri Ladabaum, a professor of gastroenterology at Stanford Medical School. The study looked at information extracted from the National Health and Nutrition Examination Survey from 1988 to 2010, which Dr Ladabaum and his team scrutinised for trends in obesity, abdominal obesity, physical activity and calorie intake over the last 20 years. The researchers made several alarming discoveries, finding that the number of US women engaging in absolutely no physical activity shot up from 19.1% in 1994 to a massive 51.7% by 2010. A similarly poor pattern emerged for men too, with the numbers rising from 11.4% to 43.5% in the same time frame. “We suspected there was a trend in that direction, but not that magnitude,” Dr Ladabaum added. “People can get exercise in other ways, but most people don't walk or bike to work, and most people are not in jobs that require physical activity.” From 1988 to 2010, the prevalence of obesity rose from 25% to 35% in women, and from 20% to 35% in men. The researchers found that for this 22-year block, proportion of normal weight men and women fell, whilst the proportion of overweight men and women was unchanged. Surprisingly, those involved in the study could not unearth evidence that people were taking in more calories each day in 2010 compared to 1988. "The one caveat here is that the amount of calorie intake was based on self-report, so it is possible people were not recalling correctly what they ate, or not reporting correctly," said Dr Ladabaum.