Americans are fighting a rising tide of obesity, and they appear to be losing the battle. The personal and public health consequences of the findings, published in a research letter in JAMA, the Journal of the American Medical Association, are costly and serious.

Among individuals, overweight and obesity raise the risk of diabetes, certain cancers, elevated blood pressure, heart disease, sleep apnea, stroke, arthritis, and mental health issues such as guilt, shame and depression. And from a public health perspective, Americans' overweight and obesity contribute to rising medical expenses and increased disability.

Obesity impaired the health and functioning of over a third of adults in 2007; by 2016, those numbers rose to nearly 40 percent.

Investigators at the Centers for Disease Control (CDC) used health data from the National Health and Nutritional Examination Survey (NHANES) to look at the rates of obesity and severe obesity in the population.

Obesity is defined in adults as a body mass index (BMI) that is above 30. Severe obesity is defined as a BMI greater than 40. In children, obesity is defined as having a weight that is greater than 95% of same-aged, same-sex children.

The trends they found are based on statistics gathered on roughly 45,000 children and adults, first in 2007 to 2008, and again in 2015 to 2016. Obesity impaired the health and functioning of over a third of adults in 2007; by 2016, those numbers rose to nearly 40 percent.

The increase in obesity in children was somewhat less dramatic, rising from nearly 17 percent to 18.5 percent, but since weight gain typically sets in a person's 20s and 30s, this figure may offer little cause for optimism.

Treating obesity is far more difficult than avoiding it in the first place. Gaining weight can change your metabolism and make it hard to lose. Bariatric surgery is increasingly sought as an option, but it is expensive and not without risk.

Prevention is the best protection from the health hazards of obesity. The simplest way to maintain a healthy weight and avoid gaining weight is to watch what — and how much — you eat. Eat smaller portions; avoid sugar-sweetened beverages; fill up on lower calorie foods like fruits and vegetables; and get regular exercise, even if it's just walking around the block.