Body mass index, or BMI, measures the ratio of your weight to your height, in order to estimate if you're underweight, normal weight, overweight or obese. Lowering your BMI means losing weight, which you can accomplish through adjustments to your diet and activity levels. Lowering your BMI as quickly as possible, however, isn't necessarily the best approach for long-term results. You'll stand a better chance of keeping the weight off and feeling satisfied if you go for slower weight loss and measure other health metrics in addition to BMI.
Set a Realistic BMI Goal
BMI gives you a general idea of your ideal weight range, so you can use it to figure out a basic healthy range for your height. To calculate your BMI, use this equation:
BMI = weight in pounds / (height in inches x height in inches) x 703.
Or you can plug your height and weight into an online BMI calculator, and it will do the math for you. A BMI below 18.5 indicates that you're underweight; a value between 18.5 and 24.9 falls into the category of healthy weight; a BMI between 25 and 29.9 counts as overweight; and a BMI greater than 30 indicates obesity.
For example, people who are 5-foot-7-inches tall have a healthy weight between 119 and 159, according to their BMI. But if a 5-foot-7-inch person weighs 110 pounds, he's considered underweight and would have to gain 9 pounds to get back to a healthy BMI. Conversely, someone who is 5-feet-7-inches tall and weighs 185 pounds would fall into the "overweight" range based on BMI and would need to lose 26 pounds to get back into the healthy range.
Because BMI is calculated based on body weight, lowering your BMI involves losing weight. Plan to lose between 1 and 2 pounds per week, which you can achieve by eating 500 to 1,000 calories less than you burn each day. Find out your calorie intake target for weight loss by using an online calculator to estimate your current calorie needs, then subtract 500 to 1,000 calories. If you have a lot of weight to lose, aim for the more aggressive 1,000-calorie deficit; if you're already lean, a 500-calorie deficit is likely more appropriate. Ensure you're eating at least 1,400 calories per day to meet your nutritional needs, and avoid forcing your body into a semistarvation state.
Once you know your approximate target weight range and your approximate rate of weight loss, you can set a realistic timeline to meet your goals. Don't worry if your planned weight loss will take months or even years -- slower weight loss is more effective than fad dieting to drop pounds quickly.
Choose Healthy Foods to Lower BMI
Making smart diet choices while you lower your BMI not only helps nourish your body with vitamins and minerals and keeps you feeling full, but it may slightly boost your metabolism. Protein, for example, has a high thermic effect because it's difficult to digest. As a result, you spend more calories breaking it down in your digestive tract. With a thermic effect of 30 percent, you'll burn 30 calories for every 100 calories of protein you eat. In contrast, you'd burn only 3 calories digesting 100 calories worth of fat and just 7 calories digesting 100 calories of carbohydrates.
To determine how many grams of protein you need each day, multiply your weight, in pounds, by 0.8 -- for a 170-pound person, that's 136 grams of protein daily. Opt for lean poultry, like skinless and boneless turkey and chicken breast; tilapia, tuna and salmon; tofu, tempeh and nonfat soy milk; nonfat dairy and eggs; and nuts, seeds and beans.
Flesh out the rest of your diet with healthy whole grains, which provide carbohydrates to keep you feeling energized; fruits and vegetables, which are concentrated sources of vitamins, minerals and fiber; dairy, which provides calcium and protein; and healthy fats, including olive oil and avocado.
Accelerate Weight Loss With Exercise
Getting more activity is key if you want to lose weight and lower your BMI quickly. Aerobic activity burns calories, which helps you create a larger calorie deficit for weight loss without cutting your food intake too much. If you're new to cardio, choose a low-impact activity you enjoy -- such as brisk walking, the elliptical machine or water aerobics -- and gradually increase the intensity as you get more fit. The higher your intensity, the better for weight loss -- intense workouts trigger "afterburn," which means you'll have a higher metabolism for hours or even up to two days after your workout. As you continue to develop your cardiovascular fitness, incorporate high-intensity intervals into your routine to further increase your afterburn.
Pair cardio with full-body strength training workouts, performed two or three times weekly. Building muscle through strength training boosts your calorie burn -- since muscle requires more calories to maintain than fat -- so you can lose weight more easily, and it keeps your metabolism high so you can keep the weight off, too.
Tracking Your Progress and BMI
Track your progress to keep a record of your results on your weight-loss journey. While you might be in a rush to get your BMI into the "normal" range, you should look at other markers of health, too. For example, measure changes in your waist size over time. As you burn away excess belly fat that was previously expanding your waistline, you're improving your health. And look out for other signs you're getting healthier -- maybe you're able to work out longer, work at a higher intensity during cardio or lift heavier weights in your strength-training workouts. Don't obsess over hitting a specific number on the scale or reaching one specific BMI. As you shed the pounds, consider how you look and feel -- not just what your weight and BMI numbers are -- as the ultimate guide to whether you've reached your goals.