Peek at your doctor’s chart, and one of the first things you may see is your BMI, front and center. BMI — or body mass index — is a measure of your relative height and weight. The calculation, which uses both your weight and height, places people into an underweight, normal weight, overweight, or obese category, and may be used as a measure to assess your risk for certain diseases.
Here’s How to Calculate Your BMI if You’re an Adult
If you’re an adult, you can calculate your BMI by taking your weight in pounds divided by your height in inches squared, multiplied by 703. (1) Or, you can check out the National Institutes of Health’s BMI calculator or the Centers for Disease Control’s (CDC) version.
According to the CDC, here are the BMI ranges: (2)
Underweight: less than 18.5
Normal weight: 18.5 to 24.9
Overweight: 25 to 29.9
Obesity: 30 or higher
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Why You Should Care About Your BMI Calculation
Why is BMI important, and how is it used? Doctors often apply BMI on an individual level, but where it is really useful is in population-based research, says Charlie Seltzer, MD, a weight loss specialist in Philadelphia. Dr. Seltzer does not use BMI in assessing his individual patients, because it’s not always useful information.
For example, you can have a normal BMI but have low muscle and a lot of fat, which is an unhealthy state to be in. Or, you can be highly muscular, and thus inaccurately categorized as overweight according to BMI. (3)
But it’s through BMI that we know how grave the statistics on obesity really are. About 70 percent of adults are overweight or obese, according to data from the National Health and Nutrition Examination Survey. (4) Likewise, one in six children and adolescents are considered obese. (5)
It’s important to know if you do fall into one of these categories. When you’re overweight or obese, you’re at higher risk for cardiovascular disease, stroke, and type 2 diabetes. An elevated risk of certain types of cancer is also vastly under-recognized, says Seltzer. Indeed, the National Cancer Institute notes that higher amounts of body fat are associated with cancers, including endometrial, esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian, and thyroid, among other types. (6)
Then, there’s how obesity can affect your day-to-day quality of life. “It can also lead to a poor quality of sleep, which makes you tired, destroys healthy habits, and makes people more overweight,” says Seltzer. High blood pressure, high cholesterol, depression, anxiety, and pain are other problems associated with obesity. (7)
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What Factors May Put You at Risk for a High BMI?
Reasons why someone becomes overweight or obese are multifactorial, but here are some contributing factors:
- Your genes Everyone was born with a unique body, and not everyone is designed to be the same. Some people may have a faster metabolism than others, for instance. However, there’s a big gray area: “If you have overweight parents, you’re more likely to be overweight, but this may also be due to lifestyle factors,” says Seltzer. (7)
- How you eat and move This means how much activity you’re getting in your day and how healthfully you’re eating. “People become obese by consuming more calories than they burn. If you do not [do that], you do not become obese,” says Seltzer. This excess weight can come on rather slowly, maybe even over decades. “Maybe you don’t notice that you gained five pounds over the holiday season, the weight continues to come on, and suddenly you’re up by 30 pounds,” he says. (7)
- Your environment Do you have bike lanes on your street? Are there sidewalks so you can walk safely? These features in your surroundings can nudge you into living a more active life. Other factors: public transportation in your area, neighborhood safety, and a family that supports doing activities together. (8)
- Medications Some medications, like those for sleep, blood pressure, and psychiatric conditions, can stimulate your appetite, says Seltzer. Others may make you feel sleepy or drowsy, possibly causing you to be less likely to work out or be active. (7)
- Medical conditions Hypothyroidism, polycystic ovary syndrome (PCOS), and Cushing’s syndrome are a few examples of medical problems that cause weight gain or make it more difficult to lose weight. (9)
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How to Help Reduce Your Risk of Becoming Overweight or Obese
If you’re looking to lose weight and move out of the obese or overweight category, some small and sustainable changes can actually make the biggest difference in your chance at success.
Take a look at what you’re eating now. You may think you have a handle on your diet habits, but most people don’t actually know what they’re eating, says Seltzer. He recommends tracking what you eat for two weeks. Often, you’ll see that there are random bites of food here or there that may add up to hundreds of extra calories each day.
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Make tiny tweaks to eat smaller portions. Make small and realistic changes to get your calorie count down, Seltzer says. (Think drinking one less glass of wine when out.) Rather than eliminating foods (even favorite foods), eat smaller portions. That may be ½ cup of ice cream instead of a cup. In total, you may end up consuming 5 to 10 percent fewer calories per day.
See whether your medications list weight gain as a side effect. As mentioned, certain medications can lead to weight gain. “Most of this can be avoided by keeping an eye on your caloric intake,” says Seltzer. One problem is that your doctor may not inform you that weight gain is a side effect of a drug they’re prescribing. Ask your doctor about common side effects for any new drug, including weight gain. Knowledge is power.
Make sure you get enough sleep. When you make sleep a lower priority, you’re setting yourself up for weight gain. “Fatigue raises cortisol [a stress hormone], which acts like an appetite stimulant,” says Seltzer. Lack of sleep can lead you to be less motivated to be physically active and more likely to reach for quick and unhealthy food. Snooze the recommended seven to eight hours a night for better weight control. (10,11)
RELATED: How Much Sleep Do You Really Need Each Night?
Manage your stress levels. Feeling tense not only can make you more prone to emotional eating, but it may also raise your levels of cortisol, leading to weight gain. (12) Plan go-to strategies that make you feel at ease (whether that’s a quick run or a chat with a friend) — use them when you feel anxiety rising.
Be kind to your gut. The gut microbiome, an environment of good and bad bacteria in your gut, may also play a role in your risk for metabolic syndrome and obesity. Eating foods that support healthy gut bacteria, such as pre- and probiotics, can help you maintain a healthy weight, research suggests. Veggies, fruit, whole grains, and legumes are examples of prebiotics, while nonfat or low-fat Greek yogurt, sauerkraut, pickles, and kimchi are examples of probiotics. You’ll also want to be mindful of antibiotics you’re taking because, when not necessary (such as for viral infections, which antibiotics cannot treat), these medications can throw off the balance of bacteria in your gut, potentially affecting your disease risk, studies suggest. (13,14)
Get in the right physical state, too. “If you’re not feeling well, you won’t be able to lose weight. Stop worrying about losing weight and start worrying about feeling better,” says Seltzer. That includes taking care of stress and sleeping more. “This will put you in a position where you can be successful.”