As BMI increases the risk of chronic disease and early death increases
BMI isn't the best way of looking at a person's weight
Diet, physical activity and avoiding tobacco are important for health
Is it possible to be both obese and healthy? It's true that obesity has long been associated with cardiovascular disease, Type 2 diabetes and several forms of cancer, but a lingering question is the degree to which obesity itself actually contributes to poor health.
For every study suggesting that as body mass index (BMI) increases, the risk of chronic disease and early death also increases, there are others demonstrating that people can be healthy - or unhealthy - at almost any body weight.
For example, a study published in July in the Lancet examined data from more than 10 million people from four continents and found that BMI outside the normal range - both underweight and overweight - was associated with an increased risk of poor health and early death. However, a similar study of more than 300,000 Korean adults, also published in July, concluded that something called "metabolic health" was more important than BMI when it comes to estimating future health risk.
Metabolic health - a term that used to be found mostly in medical research but is coming into more general use - means not only that you don't have cardiovascular disease or Type 2 diabetes but also that you don't have the precursors of these diseases - increased levels of blood sugar, blood pressure or cholesterol.
Although it's possible that genetics play a role in staving off these conditions at higher weights, how we live matters, too. Metabolically healthy obesity is more common among younger women who eat a healthy diet, are physically active and have a higher socioeconomic status. That's probably because women are more likely to seek out preventive health care, and lower socioeconomic status affects the availability of resources that support a healthy lifestyle, including healthy food, walkable neighborhoods and access to health care.
What's clear is that health is not a given; it something that's ours to be lost or gained based on the sum of our daily actions. A healthful diet, regular physical activity and avoiding tobacco use are important for protecting health and preventing disease, regardless of body weight.
But research shows that the majority of Americans are not hitting those marks.
If you want to get healthy, be healthy and stay healthy, then focusing on health-promoting behaviors is far more important than worrying about BMI. One reason is that BMI isn't the best way of looking at weight.
BMI can't tell the difference between body fat and lean muscle - or where body fat is distributed. Maintaining lean muscle supports health, especially as we age. Excess body fat can increase the risk of chronic disease, but that largely depends on where that fat is located. Subcutaneous fat (fat under the skin) is thought to carry the least risk, while visceral fat (fat around the body's abdominal organs) carries more risk, and fat deposits in the liver and muscles carry the most risk.
As for whether weight loss improves health, that depends. For healthy obese individuals who have normal blood pressure, blood sugar and cholesterol levels, losing weight has not been shown to improve those metrics any further, and in some cases it actually contributes to unhealthy physical and psychological effects, including further weight gain.
One unfortunate finding of long-term research studies is that as many as half to two-thirds of healthy obese individuals eventually become unhealthy. While it's not clear why this happens, increasing age and decreasing physical activity are likely factors. You can't do anything about growing older, but you can make a point to stay physically active.
Two other factors may be weight stigma and socioeconomic status, because they can be profound sources of stress. Stress contributes to the very health problems that increase risk of cardiovascular disease and diabetes.
Regular physical activity is vital for good health for people regardless of weight, but it also may also explain why obesity isn't always associated with metabolic health risks. Physical activity promotes stable blood sugar, blood pressure and cholesterol levels and helps maintain or build lean muscle, improving body composition.
The research studies that actually consider fitness when looking at the connection between weight and health tend to find that healthy obese individuals are fitter than their unhealthy obese peers and have essentially the same risk of chronic disease and premature death as the healthy normal-weight participants.
Physical activity doesn't have to come from just gym workouts or other planned activity, either. Anything that gets you out of your chair makes a difference. A 2015 study in the American Journal of Clinical Nutrition found that healthy obese individuals logged significantly more "incidental" activity - the type you get when you're walking to the office water cooler or puttering around the house instead of sitting on the couch - than unhealthy obese individuals, but that moderate-to-vigorous physical activity was about the same between groups.
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