The ages at which we are most susceptible to putting on weight have been revealed - 38 for women and 44 for men.
The findings show that the middle-aged spread is not a myth, with both sexes more vulnerable to weight gain in their late 30s and early 40s.
For women the key danger zone lies between the ages of 35-40, with 38% saying they were most likely to gain weight during those years.
Women picked 38 as the most destructive year of all because the prospect of turning 40 spurs many women into turning their life around and losing weight.
Of those polled, 34% said motherhood was the main reason they put on weight. Women said that they often two dinners - once with their children and once with their partners later in the evening.
Marriage was another factor in women getting a middle-age spread, with 32% of women saying they put on weight after settling down with a long-term partner.
A further 26% of women said they had "let themselves go" in their late 30s.
The results come in a new survey of 1,000 people by the diet company Forza Supplements.
The most vulnerable dieting age for men is six years later than women's, at 44.
One of the key reasons for men getting a middle-aged spread was divorce, with 22% saying it was a factor.
The average age for a man divorcing in the UK is 40-44, and single men are more likely to drink heavily and eat out more.
However, the most popular reason for men's expanding bellies was work, with 36% saying they were too busy with their careers to go to the gym.
Forza Supplements managing director Lee Smith said: ‘Weight gain in both men and women is quite normal and the process can begin at 30.
"In our early and mid-thirties we stave off weight gain because we lead busy lives – work, exercise, socialising if we’re childless. If parents, most people of this age have small children so they remain active – getting in the swimming pool themselves, riding bikes.
"By 38 for women and 44 for men, on average, the children are old enough to do these activities alone and parents tend to lead a sedentary life – between providing a taxi service for the kids."