One in three adults in the UK is now on a permanent diet, a survey suggests.
Some may obsess about losing weight
A poll of 2,000 people for supermarket giant Tesco found the over-55s were most likely to go on a diet at some stage every month.
Among this group, 15% try to restrict their calorie intake every day - double the number of any other age group.
Experts have warned that 60% of adults will be overweight by the year 2050 if action is not taken to tackle rising rates of obesity.
Alan Johnson, the Health Secretary, has warned that obesity poses a potential crisis on the same scale as climate change.
Government experts have calculated that 70,000 lives could be saved if Britons followed simple healthy eating guidelines.
However, research has suggested that "yo-yo" diets are ineffective, and may actually carry a risk of weight gain in the longer term.
The latest survey found that 15% of adults spend between 30 minutes and an hour each day worrying about their weight.
More than one in 20 women admitted to fretting about their figures for more than three hours a day.
Self-confidence was one of the main reasons respondents gave for watching what they eat.
Six out of 10 women and more than four out of 10 (44%) men said they hoped that losing weight would help them feel better about themselves.
One in five respondents were trying to lose weight to improve their love lives.
Another reason given for losing weight was to look more like celebrities, attractive friends or colleagues.
Psychologist Donna Dawson said: "Men and women in the UK have a strong desire to feel better about themselves, and one of the ways they believe they can achieve this is through dieting and losing weight.
"However, it is important to understand that constant, yo-yo dieting which is doomed to failure will only work to undermine self-confidence.
"What is needed is developing a plan for a long-term, healthy lifestyle, substituting good habits for bad, and setting goals that can be realistically achieved."
Dr Ian Campbell, medical director of the charity Weight Concern, said he was not surprised by the findings.
"I think it's important that we do take our weight seriously, and monitor our food intake and activity levels regularly.
"Two thirds of us are already overweight. However we need to move away from the concept of "dieting" towards one of "healthy diet".
"The best thing the supermarkets could do to help this would be to place their focus on healthy food choices."