The American College of Sports Medicine recommends getting at least 150 minutes of moderate-intensity cardiovascular exercise each week. Moderate intensity exercise is defined as 50 to 65 percent of maximum, and ACSM's recommendations are the most basic requirements to elicit changes in sedentary individuals. Workload and intensity should be progressively and periodically modified with gains in overall wellness.
One pound of fat is equal to 3,500 calories. To lose 1 lb., there needs to be a negative calorie balance over time. Negative calorie balance is achieved through diet, exercise, or most effectively, both. If you want to lose 1lb. of fat per week, you need to have a daily negative calorie balance of 500. To accomplish this, you need to decrease your recommended caloric intake by 500 calories, exercise that equals 500 calories, or use a combination of both by exercising to the equivalent of 250, and decreasing caloric intake by 250.
20 Minutes a Day
The number of calories you burn in 20 minutes varies with the exercise activity. Twenty minutes of walking at a moderate pace will burn 80 to 100 calories, while a high-intensity interval or cardio circuit may burn at most 250 to 300 calories.
Slow and Steady
If you burn between 80 and 300 calories a day through exercise, it will take you anywhere from 10 days to more than a month to lose 1 lb. of body fat using a program that only incorporates 20 minutes of exercise a day. Adding just five to 10 minutes a day will significantly impact calories burned.
By modifying your diet by decreasing your caloric intake, you can compound your results to lose weight about twice as fast, meaning it will take you anywhere from five to 17 days to lose 1 lb. of weight. In addition, there is a synergistic psychological effect that by exercising regularly, you are more likely to abide dietary regulations, and vice versa.
Weight loss is more significant when both diet and exercise are included, but restricting caloric intake should never exceed 500 calories less than the recommended caloric intake. This means that if you want to lose weight faster, it should be done by increasing the exercise duration and frequency. Restricting calories in excess may trick your body into believing that you are not getting enough, and may slow down your body's ability to burn calories at the highest rate. Healthy and realistic weight loss is considered to be around 1 or 2 lbs. a week.