Health care professionals use body mass index, or BMI, as a tool to assess health. Keeping your BMI within the normal range may indicate a reduced risk of developing a chronic illness such as diabetes or heart disease. If your BMI indicates you're overweight, getting it down to 21.8 may improve health. If you'd like to work on decreasing your BMI, discuss it with your doctor or a registered dietitian.
About a BMI of 21.8
The BMI is considered a reliable indicator of body fatness in adults, according to the Academy of Nutrition and Dietetics. It is a mathematical equation you can calculate yourself as long as you know your current weight and height. The BMI equation is fairly simple:
BMI = [weight in pounds / (height in inches x height in inches)] x 703.
So, a person who is 5 feet 5 inches tall and weighs 131 pounds has a BMI of 21.8 because [131 / (65 x 65)] x 703 = 21.8. Also, a person who is 6 feet tall and weighs 161 pounds has a BMI of 21.8 because [161 / (72 x 72)] x 703 = 21.8.
To get to a BMI of 21.8, a 5-foot-5-inch woman weighing 170 pounds needs to lose 39 pounds.
A BMI between 18.5 and 24.9 is considered normal weight. If your current BMI is between 25 and 29.9, you are considered overweight, or if it's 30 or above, you are considered obese. While your goal may be to get down to 21.8, getting your BMI into the healthy range is also a good strategy.
Diet Changes to Lower BMI
If you want to decrease your BMI, you need to change your diet. To start, you'll reduce your caloric intake. A pound of fat contains 3,500 calories. To lose 1/2 to 1 pound of fat weight a week, use an online calculator to obtain the number of calories needed to maintain your current weight, then reduce that number by 250 to 500 calories a day.
Cut calories using fat-free milk instead of low-fat or whole, swap out chips and cookies for fresh fruits and veggies, look for leaner cuts of meat and eat baked, steamed or broiled food instead of fried. Avoid drinking sugary beverages such as soda and juice drinks, and stick to calorie-free drinks such as water and unsweetened tea.
Including healthier, low-calorie foods also helps you cut calories to lose weight and improve BMI. Fill half your plate with fruits, and veggies and round it out with lean protein such as chicken, fish or tofu and small portions of whole grains such as quinoa or brown rice.
Exercise to Lower BMI
To get down to your desired BMI and stay there, include exercise as part of your program. For weight loss, the Centers for Disease Control and Prevention recommends 300 minutes of moderate-intensity exercise a week, which translates into a brisk 60-minute walk five days a week. Or consider shooting for 150 minutes of vigorous-intensity exercise each week, which translates into a 30-minute jog five days a week.
Add muscle and improve your metabolism with strength-training exercises two days a week. Lifting weights, heavy gardening, yoga and working with resistance bands all help build muscle.
Regular exercise also burns calories, which may allow you to be less restrictive with your diet.
Other Tools to Help You Along the Way
While the BMI is a good tool to use for your weight-loss journey, your bathroom scale and waist circumference measurements can help you monitor your progress as you reach your goal. To monitor your weight loss, weigh yourself first thing in the morning on the same day each week and keep track of your number.
Like BMI, the waist circumference measurement also assesses health risk. Wrap a measuring tape snugly -- but not too tight -- around your waist above your hip bones and take the measure as you're breathing out. For better health, men want a waist circumference measurement less than 40 inches and women smaller than 35 inches.
- Academy of Nutrition and Dietetics: Understanding Your Body Mass Index
- Journal of the Academy of Nutrition and Dietetics: Diet or Exercise Interventions vs Combined Behavioral Weight Management Programs: A Systematic Review and Meta-Analysis of Direct Comparisons
- FamilyDoctor.org: What It Takes to Lose Weight
- Centers for Disease Control and Prevention: Cutting Calories
- Centers for Disease Control and Prevention: How Much Physical Activity Do Adults Need?
- McKinley Health Center: Breaking Down Your Metabolism
- Centers for Disease Control and Prevention: Assessing Your Weight
- Baylor College of Medicine: Adult Energy Needs and BMI Calculator