The best way to lose 20 lbs. in three months is by combining dietary changes with increases in physical activity. Both diet and exercise can help you reach the caloric deficit necessary to lose excess weight. Even a goal of 20 lbs. in three months can be reached with this method. But check with your doctor before making changes in your exercise or diet plan, particularly if you have a health condition.
Caloric Deficit
According to the National Institutes of Health, it takes a deficit of 3,500 calories to lose 1 lb. of fat. Since you're looking at weight-loss goal of 20 lbs., the total deficit necessary is 70,000 calories. This may seem like a lot, but it breaks down to a shortfall in caloric intake of just under 770 calories each day. While this number is a bit more doable, it still takes commitment to hit this deficit daily.
Caloric Need
To know exactly how many calories you can consume each day to maintain your weight, you first need to know your base metabolic rate. For women, this number is equal to 655 + (weight in lbs. x 4.35) + (height in inches x 4.7) - (age in years x 4.7). For men, it's 66 + (weight in lbs. x 6.23) + (height in inches x 12.7) - (age in years x 6.8). Once you've arrived at this number, multiply it by 1.2 to determine your current caloric need without exercise. For example, a 32-year-old woman weighing 155 lbs. at 5 feet 4 inches tall has a base metabolic rate of 1,511.5 and a current caloric need of 1,813 calories without exercise.
Diet
After determining your caloric need, make adjustments to your diet to help generate the daily deficit of 770 calories needed to hit your goal. Reducing portion sizes and replacing foods high in fat and calories with fruits, vegetables and whole grains can often help you hit this number.
Exercise
It's difficult to cut 770 calories a day from your diet -- and to stay healthy, your calorie count should be 1,200 or more -- so you'll probably want to make up the difference with exercise. If you're looking at a current caloric need of 1,813 calories, eating 1,363 calories can provide a deficit of 450 calories each day. If you're able to cut 450 calories from your diet each day, you're left with another 320 calories to burn through physical activity.
A number of different activities can help you hit this number. Biking, jogging, swimming, cross-country skiing, rock climbing or taking part in a competitive sport, such as racquetball, handball, tennis, volleyball or soccer, are all known to burn close to this number in about 30 minutes.
References
- National Institutes of Health: Exercise and Weight Loss
- National Institutes of Health: Tips for Losing Weight
- MayoClinic.com: Weight Loss -- Better to Cut Calories or Exercise More?
- National Institute of Diabetes and Digestive and Kidney Diseases: Choosing a Safe and Successful Weight-Loss Program
- Harvard Medical School: Calories Burned in 30 Minutes for People of Three Different Weights
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