Making people feel ashamed about obesity could lead them to gain weight, not lose it, suggests University College London.
In a study of nearly 3,000 adults over four years, those who said they had experienced weight discrimination put on more weight than those who did not.
Researchers said there was no evidence discrimination caused weight gain, but it could lead to comfort eating.
Health professionals were urged to be more supportive.
The study, in the journal Obesity, looked at data from adults aged over 50 ranging from normal weight to obese who had taken part in the English Longitudinal Study of Ageing.
They were asked if they had experienced day-to-day discrimination that they believed to be connected to their weight.
Examples of discrimination included being treated disrespectfully, receiving poor service in shops and being harassed.
One in 20 reported weight discrimination, and in the morbidly obese group one in three reported discrimination.
Men and women reported similar levels of weight discrimination.
Over the four-year period, on average, people in all weight groups who said they had experienced these negative attitudes put on nearly 1kg - just over 2lb.
Those who did not typically lost 0.7kg.
The researchers say this suggests that blaming and shaming people for being overweight is counterproductive.
Instead they say it is better to be supportive and encouraging.
Dr Sarah Jackson, lead study author from the department of epidemiology and public health at UCL, said: "There is no justification for discriminating against people because of their weight.
"Previous studies have found that people who experience discrimination report comfort eating.
"Stress responses to discrimination can increase appetite, particularly for unhealthy, energy-dense food.
"Weight discrimination has also been shown to make people feel less confident about taking part in physical activity, so they tend to avoid it."
The study said "widespread weight bias" had been reported in health professionals, and not just among the general public.
Prof Jane Wardle, director of the Cancer Research UK Health Behaviour Centre at UCL, said weight discrimination was part of the obesity problem - not the solution.
"Everyone, including doctors, should stop blaming and shaming people for their weight and offer support, and where appropriate, treatment."