Sometimes referred to as: obesity, overweight, underweight, weight loss, weight management
Obesity is defined as a body mass index (BMI) of ≥30 kg/m2. Being underweight is a BMI of under 18.5 kg/m2
Cases Per Year (US)
Over 70 million adults in the U.S. are obese. 99 million are overweight.
39.6% of the U.S. population is obese. This prevalence varies by region.
Moderate to high
Fundamentals of Weight and Health
How much weight is too much or too little from a health perspective?
BMI is a standardized calculation that uses weight and height to aid in determining a healthy weight. A normal BMI is considered to be 18.5-24.9 kg/m2. A BMI of >24.9 is overweight, and a BMI of 30 or greater is obese. A BMI >40 is severely obese. In contrast, a BMI below 18.5 kg/m2 is underweight.
Other tools that can be used to determine healthy weight include waist circumference, waist-to-hip ratio, body fat percentage via skinfold thickness and bioelectric impedance. You can find a list of normal values for waist circumference and waist-to-hip ratio here.
Can you be overweight and still be healthy?
Overall, it’s important to note that BMI isn’t everything! For example, one recent study showed that fit people with an obese BMI had similar metabolic and cardiovascular risk profiles to normal-weight individuals. Longer-term studies are needed for a more complete comparative analysis, but the point is that BMI as a measurement doesn’t tell us anything about factors like body composition or weight distribution, both of which affect how healthy someone actually is.
For instance, while excess fat anywhere can have negative impacts on hormone function, extra weight around the abdomen confers more metabolic risk to someone than extra weight carried in the thighs.
How can you tell if your weight is affecting your health?
There are certain measurements that doctors can use to help determine if your health is being affected by your weight. Blood tests include cholesterol panels, blood sugar levels (glucose and hemoglobin A1c), and sometimes the inflammatory marker C-reactive protein. We also assess metabolic health by measuring blood pressure.
Even without any of this, if you find your weight is holding you back from accomplishing things you'd like to be able to do–or if you feel inhibited by heaviness that is causing joint pains or other discomfort–then your weight is affecting your health.
The term “skinny-fat” gets used a lot. What is that?
This non-medical term is usually used to describe people who have an overall thin body appearance, but who have a higher body fat percentage than is healthy for their size.
These individuals typically have a normal BMI, but this fact can be misleading because they may still be at higher risk for weight-associated complications, especially if they carry excess weight in their midsection. One recent study found that this population had an increased overall mortality rate.
Are there any long-term consequences from being over- or underweight?
Yes. Greater BMI is associated with an increased rate of death from ailments such as cardiovascular disease, stroke, diabetes, kidney disease, and various cancers (colorectal, breast, uterine, esophageal, kidney, and pancreatic). The risk is higher if you also have markers such as high LDL cholesterol, low HDL cholesterol, signs of insulin resistance, and high blood pressure.
It’s important to know that the same BMI can mean very different things in different populations. For example, overweight people of Asian heritage tend to have a higher mortality risk at a BMI of 25 than do other groups. This has prompted some to recommend that a BMI of 23 be used as a cutoff to better ascertain risk in that population.
Being underweight also poses certain health risks. It can lead to a weaker immune system, decreased bone density, vitamin deficiencies, difficulty conceiving, and anemia. A study done in 2017 demonstrated that being underweight was associated with an overall increased mortality risk.
What are some reasons for weight gain and weight loss?
Changes in eating habits, physical activity level, or certain medications, as well as inadequate sleep, stress, and various health conditions can result in weight gain or loss.
Some conditions that may contribute to weight gain include underactive thyroid, polycystic ovarian syndrome (PCOS), sleep apnea, and depression.
Conditions that can contribute to weight loss include overactive thyroid, digestive issues, chronic obstructive pulmonary disease (COPD), and depression. Often, weight changes can be related to multiple factors.
Strategies for Losing Weight
Strategies for Gaining Weight
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Jenna Katzman, NP and Nora Lansen, MD are both members of the Galileo Clinical Team. Connect with one of our physicians about Healthy Weight or any of the many other conditions we treat.Join Today