A person gains weight when the energy you consume is more than the energy you spend. So either increasing your exercise, energy spent or decreasing food you consume can lead to weight loss. So if you want to keep your intake intact you have to increase your energy expenditure ie increase your exercise. Please refer to the following links: https://www.webindia123.com/health/diet/diet/ideal.htm, https://www.webindia123.com/health/diet/calorie/calorie.htm, https://www.webindia123.com/health/diet/calorie/weight.htm, https://www.webindia123.com/health/diet/nutrie/nutrients.htm