The number of morbidly obese people in England, Scotland and Wales is set to double over the next 20 years, according to a recent study.
If current trends continue, nearly five million Brits will have a Body Mass Index (BMI) above 40, up from 1.9 million in 2015, researchers say.
The highest levels will be seen among English men aged 55 to 64 years old, with the number of adults in England set to raise from 3% in 2015 to 8% in 2035 according to the analysis.
More than 10% of adults in Wales are predicted to be morbidly obese within the same time frame.
Global airline passenger traffic expected to double in 20 years
The research, by the UK Heart Forum and Institute of Technology, Sligo, in Ireland, will be presented at the European Congress on Obesity in Vienna, Austria.
The authors said: "Our study reveals a worrying picture of rising morbid obesity across England, Wales and Scotland that is likely to weigh heavily on healthcare systems and economies.
"Strong measures to reverse this future trend must be an important public health priority."
Morbid obesity - the most extreme forms of obesity - is understood to be linked to heightened risk of chronic diseases such as Type 2 diabetes, heart disease, stroke, mental illness and some cancers.
A BMI of above 25 means a person is classed as overweight and above 30 means they are obese.
If a person has a BMI of 40 or more, or 35 or more and experiencing obesity-related health conditions, such as high blood pressure or diabetes, they are classed as morbidly obese.
Earlier this month, a new study suggested that a piece of string could be a more accurate measure of body fat than the traditional BMI weight against height calculation.
The simple test measures waist circumference using a piece of string the length of the person's height, folded in half.
