Cancers associated with being overweight or obese account for 40% of all diagnoses of the disease in the United States, an increasing share of all cancer diagnoses nationwide.

Although new cases of cancer have fallen since the 1990s, diagnoses of overweight- and obesity-linked cancers increased between 2005 and 2014, according to a new report from the Centers for Disease Control and Prevention. Being overweight is associated with increased risk for 13 types of cancer.

“When we step back and lump together all the types of cancer associated with overweight and obesity, we saw a direction upwards,” said Anne Schuchat, deputy director of the CDC.

“That’s not a smoking gun, but it’s a note of caution for us.”

Researchers at the CDC used data from the US Cancer Statistics database from 2005 to 2014, looking specifically at cancers the International Agency for Research on Cancer classifies as linked to being overweight.

The study looked at cancers more likely to occur in people who are overweight or obese. These cancers are linked to being overweight, but are not necessarily caused by being overweight.

The study found that between 2005 and 2014, the rates of overweight-linked cancers increased 7% (not including colorectal cancer), while rates of cancers not associated with obesity declined 13%. In effect, increased rates of overweight-associated cancers slowed the trend of decreasing cancer cases nationally.

“Our report found an increase in a number of types of cancers associated with obesity and overweight, at a period when the prevalence of obesity and overweight has increased substantially in the middle ages,” said Schuchat. “The prevalence of obesity and overweight is starting to show up in our cancer statistics.”

The rate of Americans who are considered overweight by the CDC has steadily climbed since the mid-20th century and now stands at two out of three.

In 2014, roughly 630,000 people in the US were diagnosed with overweight- or obesity-linked cancer. Two-thirds of those cases were in Boomer-generation adults, between 50 and 74.

Women also faced a disproportionate risk of being diagnosed with such cancers. More than half (55%) of all cancers diagnosed in women are linked to being overweight, compared with a quarter (24%) in men.

A handful of overweight-linked cancers occur only in women, including cancer of the ovary or endometrium lining of the uterus. The risk of breast cancer, which occurs overwhelmingly in women, is also linked to being overweight.

While researchers found strong links between cancer risk and being overweight for 13 cancers, not all risks are equal. For example, endometrial cancer is particularly linked to being overweight.

For every increased kilogram per square meter, the standard measurement of body mass, a woman’s risk of developing endometrial cancer is increased 8%, compared with 5% for kidney cancer, and 2% for breast cancer.

Researchers are still exploring why the risk of some cancers increases with being overweight, and whether the cancer-linked forces unleashed by being overweight are reversed once people lose weight.

“The question is whether the mechanisms that are turned on in the process of overweight and obesity can be turned off,” said Schuchat.

While rates of obesity-linked cancers rose overall, rates of colorectal, ovarian and meningioma cancers declined. In the case of colorectal cancer in particular, researchers credited improved screening.

Increased screening rates have been linked to free colonoscopies made available to seniors under the Affordable Care Act. Previously, colonoscopies cost seniors $275.

Schuchat cautioned the causes of increasing cancer rates are complex. For example, increased rates of the viral liver disease hepatitis C could account for some increase in rates of liver cancer, as could fatty liver disease, which is associated with both alcohol use and obesity. Nevertheless, she said the trends are “concerning”.

Theodore Brasky, a professor and researcher at the Ohio State University, not associated with the study, called America’s obesity problem “massive”.

“It’s interesting when we talk about cancer in this country, we talk about beating cancer and the cancer moonshot initiative, but all of these things are focused on treating cancer, curing cancer,” Brasky said. “What we need to talk about is preventing cancer, eating better.”

“Those approaches are cost effective and have a bigger impact. It’s so much easier to not get cancer than to have to deal with treating it,” he said.

CDC researchers said the risk of 13 cancers is increased by being overweight or obese, including cancer of the thyroid, gallbladder, liver, kidney, colon and pancreas. Being overweight also increases the risk of a blood cancer called myeloma, a spinal cancer called meningioma, a type of esophageal cancer, and a type of stomach cancer.

In women, being overweight is linked to cancer of the uterine lining called the endometrium, ovarian cancer and breast cancer.