The American Cancer Society study, which used data covering half the United States population, found that six cancers known to be related to obesity were rising fastest among those under 50. Each successively younger age group experienced a greater percentage increase.
In contrast, rates in successive younger age brackets declined or stabilized in all but two of 18 non-obesity related cancers, including smoking-related and infection-related cancers.
The researchers noted that young adults still have an overall lower risk of developing these cancers, compared with older adults.
Dr Ahmedin Jemal, from the American Cancer Society, said: 'Our findings expose a recent change that could serve as a warning of an increased burden of obesity-related cancers to come in older adults.
However, according to Brenda Birmann, a doctor at Brigham and Women's Hospital in Boston, Massachusetts, obesity is only one factor that could be leading to increased cancer rates among young adults.More news: Jussie Smollett was hesitant to report attack, according to police report
Although the link between obesity and cancer is not clearly understood, it is generally believed that excess body fat can affect the immune system and levels of certain hormones such as insulin and estrogen, factors that impact cell growth, and proteins that regulate how the body uses certain hormones.
And scientists are clear that losing even small amounts of weight can help reduce the risk of cancer. "And we know in people that obesity is associated with an increase in cancer and a worse prognosis for patients who have cancer".
The findings are based on 20 years of data (from 1995 to 2014) for 30 cancers in 25 states; the data was obtained from the Cancer in North America database of the North American Association of Central Cancer Registries.
Excess body weight is a known carcinogen, the American Cancer Society adds, and younger people are experiencing obesity earlier and for more prolonged periods of their lives. Especially striking was the rising rate of kidney cancers.
Research suggests bowel cancer, womb cancer, oesophageal (food pipe) cancer, cancer of the kidney, liver, upper stomach, gallbladder, ovarian, thyroid, meningioma (a type of brain tumour) and multiple myeloma (a type of blood cancer) and breast cancer in women after the menopause have all been linked to obesity. For example, in pancreatic cancer the average annual change was equal or less than 1% in people aged 40 to 84, 1.3% in those aged 35 to 39, and 2.5% in 30 to 34-year-olds.More news: Woman, 79, Died After Being Struck By Foul Ball At Dodger Stadium
In the youngest age group, 25 to 29 years, it was 4.3 per cent. Separating data into five-year age cohorts, they found that incidence of six cancers - colorectal, endometrial, multiple myeloma, gall bladder, kidney and pancreas - out of the 12 related to obesity in adults between the ages of 25 and 49 increased significantly between 1995 to 2014.
Rates for six of 12 cancers related to obesity have been increasing in successive generations of young adults, with the sharpest increases in the youngest age groups, researchers report in The Lancet Public Health. Cancer prevention will most likely involve "prevention of other things that might precipitate cancer", said Jakicic, who wasn't involved in the study. Of course, obesity is only one factor - the environment, genetics and other issues also play roles, the BBC points out.
Obesity is now one of the most preventable causes of cancer, responsible for around one in 20 cases in the United Kingdom and one in 12 in the US.
Obesity is now one of the most preventable causes of cancer in both the U.S. and the United Kingdom - around 1 in 12 cases in the USA are caused by excess weight and more than 1 in 20 in the UK.More news: Japan's finance minister apologises for criticising childless citizens