Your BMI and diabetes: What's the connection?

You might be familiar with body mass index (BMI) as a way to determine whether your weight is considered appropriate for your height. But you may be wondering about BMI and diabetes management, and whether there's a link between BMI and overall blood glucose levels. Here's what to know.

What to understand about BMI ranges

BMI is a calculation of your weight compared to your height. Researchers use BMI when they want to compare whether body weight is linked to something else they might be studying. For example, a researcher might want to investigate how BMI is linked to the number of minutes people exercise or whether a group of people above a particular BMI is more likely to develop knee problems.

On an individual basis, healthcare providers use BMI to assess whether a patient's weight status places them at risk of any conditions linked to being underweight or overweight. For most people, BMI is a pretty accurate reflection of extra body fat.

These are the Centers for Disease Control and Prevention's BMI ranges:

• BMI less than 18.5 = Underweight
• BMI 18.5 to 24.9 = Healthy
• BMI 25 to 29.9 = Overweight
• BMI 30 or higher = Obese

Two people with different heights and weights can have the same BMI. For example, a person who is 5 feet, 1 inch tall and 125 pounds has a BMI of 23.6, as does a person who is 6 feet, 2 inches tall and 184 pounds. These people would have different appearances but roughly the same amount of weight on their frames for their heights.

Unless you're unusually muscular, maintaining a BMI between 18.5 and 25 is ideal for long-term health. Of course, there's an exception to every rule including this one: People with lots of extra muscle such as weight lifters and bodybuilders may have a high BMI but very little fat on their bodies. For those people, BMI doesn't work well as an indicator of whether they're overweight or obese — a skinfold caliper test is a better measurement of body composition.

Balancing your BMI and diabetes

Although there's no association between type 1 diabetes and BMI, the risk of developing type 2 diabetes goes up as BMI increases. Generally, the higher a person's BMI, the more insulin they need. Extra fat on the body may cause insulin resistance and lead to higher insulin requirements. A high BMI is also associated with other health conditions, such as cardiovascular disease and some cancers.

Low BMI and diabetes management

If you have diabetes and your BMI places you in the "underweight" range, it's possible you have a small frame and high metabolism, resulting in a body weight that's actually fine for you but falls outside the "normal" range on the BMI scale. There are also a couple of other scenarios that may need to be considered:

• Weight loss can be a symptom of high blood sugar levels. When there's too much sugar in the blood, the body "spills" sugar into the urine. If your blood sugar routinely runs over 200 milligrams per deciliter, talk to your healthcare provider ASAP.
• It's also possible that in an attempt to keep your blood sugar levels low, you're not eating enough calories. If your blood sugar is in range, but you often feel hungry, you may need to add more fat and protein to your diet so that you can have more energy and gain weight slowly, until your BMI is in the normal range.

High BMI and diabetes management

If your BMI puts you in the "overweight" or "obese" categories, you're not alone — almost three-quarters of U.S. adults are in those categories. If you have diabetes, a high BMI means you'll probably require more insulin (or oral medication) than the average person to keep your blood sugar in check.

Daily exercise can help with insulin resistance and weight management. A high-fiber diet including lots of vegetables can also help you feel full without eating too many carbs.

Healthcare providers sometimes prescribe medication conservatively because they don't want to overmedicate and cause low blood sugar, which is dangerous. But if you have a high BMI, you may need more insulin or medication than most people. Consult your doctor to understand what the right amount of insulin is for your BMI. Also, be sure to keep an eye on your blood sugar and make sure it stays in range. If your blood sugar is routinely elevated, call your healthcare provider to discuss your blood sugar readings.

Considering BMI and longevity

In the past, malnutrition and being underweight were significant health problems in countries around the world. In the second half of the 20th century, access to inexpensive, high-calorie foods led to a different kind of malnutrition. Modern malnutrition is often a case of taking in too many calories but too few nutrients. The World Health Organization (WHO) lists obesity as a risk factor for chronic conditions, including heart disease, diabetes, arthritis, and certain types of cancer, and the WHO recognizes the noncommunicable disease as a "major challenge for sustainable development" around the globe.

Want to know more about using exercise to achieve a healthy BMI? Read tips for safely breaking a sweat with diabetes.