There’s a great many reasons why a woman's weight may fluctuate. Some might say it's a hectic work schedule preventing them from getting to the gym.
Others may suggest it's the temptation of the office chocolate machine.
But research suggests there's only one real reason - their men.
A study into the ups and downs of the female weight-cycle showed happiness - or the lack of it - in a relationship is the biggest factor.
The report found early courtship usually brings with it a strict diet regime resulting in the loss of around 5lb.
After women enter Stage 2, which is the comfort zone, when they feel secure enough to relax a little, can put on a few pounds.
Wedding plans mean another sprint to shed a few pounds before the arrival of a baby reverses that weight loss, followed by a reinvention - which again sparks a diet drive.
The five stages of weight fluctuation, which can vary over around two stone, emerged in a study of 3,000 women by UK weight management firm www.slendex.com.
'Our emotions and relationships have an enormous effect on our health and above all our weight,' said Jane McCadden, of Slendex.