When you are 40 years old, your metabolism is slower than it was 20 or even 10 years ago -- a circumstance that can make weight loss more difficult than it was previously. The key is determining how many calories you burn doing a given activity and adjust the time to accommodate your weight loss needs.
Your Current Weight
How much exercise you must do to lose weight depends on how much weight you have to lose. If you have only 5 lbs. to lose, a half-hour walk several days a week will likely rid you of the extra weight. If you have 50 lbs. to lose, you'll need to do more than that to lower your weight in a more timely fashion. A person who weighs 190 lbs. and cycles for an hour each day can burn 689 calories, which will result in a weight loss of approximately 6 lbs. per month. A person who weighs 145 lbs., on the other hand, will burn only 526 calories doing the same exercise and will likely lose about 4.5 lbs. each month.
Your Level of Fitness
Your level of fitness can also determine how much you need to exercise to see a difference on the scale. If you're very fit, running for half an hour at a 6 mph pace will burn approximately the same number of calories that a less fit person will lose walking at 3 mph for an hour. If you run for an hour, you'll lose even more. The more strenuous exercise that you're able to do, the faster you're likely to lose weight. But don't despair if you're out of shape. It's a common scenario for many people after reaching middle age. The good news is that you can begin to get fit at any age.
If you have 20 lbs. to lose and you don't care if it takes an entire year to lose it, you won't need to exercise nearly as much as a person who has the same amount of weight to lose but who wants to lose it in a three-month period. Multiply the number of pounds you want to lose by 3,500. The result is the number of calories you must burn to achieve your goal weight. Next, divide this number by the number of days you're giving yourself to lose the weight. For example, a person who wants to lose 20 lbs. must burn 70,000 calories. To lose the weight during a three-month period, that individual needs to create a calorie deficit of 777 calories each day. Use an exercise calorie calculator to determine how many calories you burn doing your preferred activity and adjust the time as needed. This equation works regardless of age.
Diet and Exercise
Exercise alone can help you lose weight. Nevertheless, if you combine it with a healthy low-calorie diet, you'll shed pounds much faster. Once you've reached 40 years of age, you may have entrenched eating habits that are less than healthy. Work to change these habits and you'll experience fewer weight problems. Watch your food intake carefully to ensure that you don't inadvertently eat more calories each day -- as increased hunger is a possibility when exercising. Banish hunger pangs by eating a diet that includes plenty of protein and no refined carbohydrates. Fill up on fiber-rich vegetables to stabilize your blood sugar. Not only will you lose weight, but you'll have more energy to work out.