Why can we put on weight with ease but have to struggle hard to lose it all? Experts have raised several new ideas regarding the subject, according to media reports Monday. Dr. David Ludwig, director of the \"Optimal Weight for Life\" program at Children\'s Hospital Boston, said in the Journal of the American Medical Association, \"Our bodies don\'t gain or lose weight indefinitely. Eventually, a cascade of biological changes kicks in to help the body maintain a new weight. Hormones and brain chemicals that regulate your unconscious drive to eat and how your body responds to exercise can make it more difficult to lose weight\". Also using the phase unconscious drive or mindless eating, Dr. Brian Wansink in his landmark book, \"Mindless Eating - Why We Eat More Than We Think,\" wrote that eating some tasty but less-than-healthy snacks or drinking a few sodas or alcoholic beverages can add on unaccounted calories real quick, but burning those off can take a lot longer and require serious efforts. \"The more diets you\'ve been on, the harder it becomes to lose weight,\" said Dr. Kelly Brownwell, director of the Rudd Center for Food Policy and Obesity at Yale University. He considered the so-called weight cycling or yo-yo dieting can affect people\'s physical well-being and change the physiology. \"When you are dieting, a hunger hormone called ghrelin increases and a fullness hormone called leptin decreases, so you feel hungrier.\" \"Moreover, frequent yo-yo dieting can make you lose muscle mass which will be replaced by fat when you regain weight,\" he added. Except the reasons presented above and the common factors as eating pattern change and exercise that affect one\'s weight, age also contributes to weight gain,he said. \"As you get older, your metabolism slows down and you need less food and calories. But if you don\'t change your caloric intake to meet the metabolism, you will surely start to see weight gain. Therefore if you really want to control weight, an all-around healthy lifestyle might be the best choice, which is, as always, healthy eating, regular exercise, managing stress and getting enough sleep,\" he concluded.