For many, weight can be a heavy topic — for many reasons beyond physical appearance. Obesity, after all, is a complex disease with causes beyond just diet and exercise. Sleep, stress and genetics also play a role.

Maybe most importantly, society and policy decisions can have a profound impact. From the availability and affordability of healthy foods to the accessibility of safe places for physical activity and more, underappreciated forces affect what we eat or how often we move.

Today, two out of every five U.S. adults are considered obese, a term used by the body mass index (BMI), a calculation tool designed to measure body fat based on a person's height and weight. A BMI of 18.5 to 20 could be considered a healthy weight, 25-30 may be considered overweight, while a BMI of 30 or greater may be considered obese.

BMI dates back to the 1800s, but many experts today find the tool to be flawed. They argue that its categories of normal weight, overweight and obese don't equate to either healthy or unhealthy. Nor does it account for a person's fat-to-muscle ratio.

(Related: PODCAST: When BMI is Helpful and When It's Not)

That said, BMI does give doctors a starting point in terms of a person's health. In general, the higher a person's BMI, the more likely they are to hold onto visceral fat — otherwise known as belly fat — which is harmful to your health. Overweight and obese patients with a waist circumference more than 35 inches for women and 40 inches for men generally indicates an unhealthy amount of visceral fat.

Patients with an excess of visceral fat are generally at a higher risk for diabetes, heart disease and stroke. What else? Explore the effects that excess weight can have across nearly every organ in the body.

What's Your Risk? Talk to Your Doctor

BMI is just a number. It's not indicative of any condition or disease but, as mentioned, can be a starting off point to have a conversation about your weight with your doctor. Talk to your doctor to know where your health stands and check out our weight-loss programs for more information.