The number of obese adults in Massachusetts, along with related diseases and health care costs, could rise dramatically over the next two decades if actions aren’t taken now to change the trend, according to a new report.

Nearly half of adults in Massachusetts - 49 percent - are projected to be obese by 2030 if the current trajectory continues, concludes the report released Tuesday by the Trust for America’s Health and the Robert Wood Johnson Foundation, two non-profit organizations that focus on improving health.

Fewer than a quarter of adults in the state, approximately 23 percent, were reported to be obese last year, according to the latest data from the US Centers for Disease Control and Prevention.

By 2030, Massachusetts could save roughly $14 billion in cumulative obesity-related health care costs, the report estimates, if the state were more aggressive in its anti-obesity programs.

It suggests that all states could prevent many obesity-related diseases, and significantly reduce related health care costs, if they helped residents reduce their body mass index, which is a calculation that uses height and weight to estimate a person’s body fat. An average of 5 percent reduction in body mass index, or BMI as it is commonly known, among adults in Massachusetts could potentially reduce obesity-related health care costs by about $5 billion by 2020, the report said.

The report recommended several policy changes be adopted nationwide to attack obesity, including updating nutrition standards for snack foods and beverages in schools—actions Massachusetts has taken—making physical education and physical activity a priority, and more robust support for healthy nutrition in federal food programs that help low income families.

An average 5 percent reduction in body mass index among adults in Massachusetts, the report said, would translate to approximately 77,000 fewer cases of type 2 diabetes, 65,000 fewer instances of heart disease and stroke, and nearly 76,000 fewer cases of high blood pressure.

As high as the obesity numbers are in Massachusetts, there are fewer obese adults here than in most other states, the report said. Only Hawaii and Colorado, had lower current obesity rates. The state with the highest rate was Mississippi, at 35 percent, followed by Louisiana with 33 percent.

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By Kay Lazar, Globe Staff