A report by the Health Select Committee says health workers should use every opportunity to deal with the problem.
The MPs also call for urgent steps so people understand the wider health benefits of physical activity.
The government says its Change4Life programme is providing widespread free advice on healthy eating and exercise.
But the MPs argue that national and local government and the NHS must do more to prevent people becoming unwell.
That could include regulation of what goes into food, a ban on marketing sugary drinks to children and much more support for people at risk of obesity and diabetes, so they do not need bariatric surgery.
The MPs also highlight inequalities in rates of physical activity, in particular the disparity between men and women.
Official figures suggest just 16% of girls aged five to 16 achieve recommended levels of physical activity, compared with 21% of boys.
Just 32% of women meet the recommended threshold for activity, while for men the official figure is 43%.
The report speaks of a “fear of judgement” deterring many women from taking exercise.
One witness to the committee, Julie Creffield, described the ordeal of venturing out.
“I have women who tell me they run on a treadmill in their shed because they just don’t want to be seen in public, but that is part of the problem. Because we don’t see many overweight women exercising in public, other women don’t think that exercise is for them.”
Source: Health Select Committee