More than half of America’s youngest adults — 56 percent of those ages 18 to 25 — are overweight or obese, according to Johns Hopkins research, published in JAMA.

Using data from a nationally representative sample of 8,015 people in that age bracket, the researchers compared average weights over the past four decades. In that time, that population’s average body mass index (BMI), a measure of body fat based on a person’s height and weight, had increased by 4.6 points — from 23.1 (considered normal weight) to 27.7 (considered overweight). That shifted the number of overweight young adults from about 18 percent in the late 1970s to nearly 24 percent by 2018.

The biggest spike in weight measurements, however, was in the prevalence of obesity, which increased from about 6 percent to nearly 33 percent. The percentage of those with a BMI indicating a normal weight (18.5 to 24.9) dropped from about 69 percent to 38 percent. BMI matters because being overweight or obese puts you at risk for a range of health problems, including high blood pressure, heart disease, osteoarthritis, Type 2 diabetes, sleep apnea and some cancers.

To determine your BMI, you can do the math yourself (divide your weight, in kilograms, by the square of your height, in meters — BMI is calculated in metric measurements) or let an online calculator do the computation. For those whose BMI falls in the overweight or obese category, indicating excess body fat, health experts generally encourage a change in eating habits and behaviors. In essence: Move more, eat less.

— Linda Searing