What Are the Risk Factors for a High BMI?

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 places people into an underweight, normal weight, overweight, or obese category, and may be used as a measure to assess your risk of certain diseases.

There are four main categories of BMI for adults: Below 18.5 is considered underweight; 18.5 to 24.9 is normal or healthy weight; 25.0 to 29.9 is overweight; and 30.0 and above is obese, according to the Centers for Disease Control and Prevention (CDC).

Doctors often apply the measurement 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. BMI does not distinguish the composition of the weight, whether it's made up of fat, muscle, or bone mass, and it doesn’t account for where the fat is found on the body, the Department of Health and Human Services notes. It also doesn’t account for body differences between men and women or among people of various ethnicities, which means results can be skewed. “For example, non-Hispanic Asian adults tend to have more complications of excess weight at lower BMIs than other races do,” says Linda Anegawa, MD, a Honolulu-based double board certified physician in internal medicine and obesity medicine and the medical director of PlushCare, a virtual health platform. “There are serious flaws with relying only on BMI,” Dr. Anegawa says, adding that it should be used simply as a screening tool.

Still, it’s through BMI that we know how grave the statistics on obesity really are. More than 80 percent of adults are overweight or obese, per the National Institutes of Diabetes and Digestive and Kidney Diseases. Likewise, nearly one in five children and adolescents are considered obese, per CDC data.

Overweight or obesity are linked with a higher risk of heart disease, stroke, and type 2 diabetes, according to the CDC. A high BMI could also be associated with an elevated risk of certain types of cancer, an often underrecognized relationship, says Seltzer. Higher amounts of body fat are associated with endometrial, esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian, and thyroid cancers, among other types, the National Cancer Institute notes.

An elevated BMI may also affect brain health. One large cross-sectional study published in the June 2019 issue of Radiology found that participants with a BMI of over 30, which is considered obese, had smaller brain gray matter volumes and other structural differences than a group of non-obese adults. These are possible markers of cognitive decline.

Then there’s how obesity can affect your day-to-day quality of life. “It can lead to a poor quality of sleep, which makes you tired, destroys healthy habits, and makes people more overweight,” says Seltzer. Obstructive sleep apnea, a common sleep disorder that causes tiredness and is associated with various health issues and conditions — from anxiety to poor focus — is also associated with obesity, per a 2017 article in Sleep Medicine and Disorders.

What’s more, obesity is linked with high blood pressure, high cholesterol, depression, anxiety, and pain, according to the CDC.

Risk Factors for a High BMI

The reasons why someone becomes overweight or obese are multifactorial, as the National Heart, Lung, and Blood Institute notes. The following are some of the factors.

Genetics

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. But 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.

A Suboptimal Diet and Physical Inactivity

As mentioned, various phenomena contribute to the onset of obesity, and your genes and other factors you can’t control can certainly play a role. Two you can control, though, are diet quality and physical activity. A diet high in calories and low in important nutrients, in addition to a lack of exercise, can contribute to obesity, causing gradual weight gain. “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,” Seltzer says.

Environmental Factors

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, and they may not be factors can control. Other factors include access to healthy food and high quality grocery stores, not to mention how your workplace is set up (do you have access to standing desks or are you confined to a desk chair all day?), per UCSF Health. What’s more, public transportation in your area, neighborhood safety, and a family that supports doing activities together can make obesity easier to manage or prevent, according to the Harvard T.H. Chan School of Public Health.

Certain Medications

Some drugs, like those for sleep, blood pressure, and psychiatric conditions, can stimulate your appetite, says Seltzer. Others may make you feel sleepy or short of breath, possibly causing you to be less likely to work out or be active, according to the University of Rochester Medical Center.

Some Medical Conditions

Prader-Willi syndrome and Cushing’s syndrome are two examples of medical problems that cause weight gain or make it more difficult to lose weight, according to the Mayo Clinic.

If you’re looking to lose weight and lower your BMI, small and sustainable changes can actually make the biggest difference in your chance of success. While everyone is different, a well-rounded healthcare team — complete with a mental health care specialist, a registered dietitian-nutritionist, and a primary care doctor, as well as any specialists — may be critical for meeting your individual goals. That said, here are some recommendations for your personal role in weight management, from Seltzer and researchers.

Keep a Food Journal

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. Either a smartphone app or paper notebook will work. 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. It’s these small things that often matter more than your adherence to an of-the-moment diet or whether you eat (or avoid) specific foods or food groups.

In one study, published in the February 2020 issue of Obesity, that looked at the behaviors and habits of people who lost weight, those who successfully kept it off for more than three years were more likely to set food intake goals, measure their food, and record what they ate compared with a control group. They were also more likely to ignore cravings and practice making healthy eating choices so that prioritizing nutrition became automatic.

Although conducted by researchers at California Polytechnic State University, the study received a grant from WW, formerly Weight Watchers, a program built on behavioral change. When industry or a specific company directly or indirectly funds a study, there’s always the chance that the results may be skewed in that donor’s favor.

In any case, it’s worth noting that you can develop these small habits without a commercial weight loss program.

Practice Portion Control

Make small and realistic changes to get your calorie count down, Seltzer says. (For example, one less glass of wine when dining out.) Rather than eliminating foods (even favorite foods), just eat smaller portions. Maybe that's ½ cup of ice cream instead of 1 cup. In total, you may end up consuming 5 to 10 percent fewer calories per day.

Look at Your Medication Labels

Specifically, see whether your medication lists weight gain as a side effect. As mentioned, certain drugs can lead to weight gain directly or indirectly. “Most of this can be avoided by keeping an eye on your caloric intake,” says Seltzer.

Your doctor may not always inform you that weight gain is a side effect of a drug she's prescribing. Ask about common side effects for any new drug, including weight gain. Knowledge is power!

Get Enough Quality 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 increase your risk of being overweight or obese because it can lead to dysfunctional eating, less motivation to be physically active, and metabolic changes, according to a study published in Medicine in 2019. Try to snooze for the recommended seven to nine hours a night, as the Sleep Foundation recommends.

Find Ways to Manage Stress

Feeling tense not only can make you more likely to reach for unhealthy foods and overeat, but it may also affect where you store fat, according to one study. The authors cited research suggesting that chronic psychological stress causes the accumulatation of belly fat, which is most strongly associated with health issues like heart disease.

Employ stress-reduction 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 and other microbes in your gut, may also play a role in your obesity risk, according to a review in the February 2020 Annals of the New York Academy of Sciences. Foods that support healthy gut bacteria, such as pre- and probiotics, can help you maintain a healthy weight.

Bananas, whole grains, and greens are examples of prebiotics, while yogurt and sauerkraut are examples of probiotics, per the Mayo Clinic. 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 drugs can throw off the balance of bacteria in your gut, potentially affecting your risk of infection and immune function, according to research.