Dame Helen, who turns 69 on Saturday, says she is a 'classic yo-yo dieter'.
She has always fluctuated by 10lb - and is currently at the top end of those 10lb! But rather than hit the gym, she said that it takes her just 12 minutes of exercise a day to keep herself fit.
She follows the Royal Canadian Air Force exercise plan, which was created by a doctor in the 1950s. It is a stretching and toning regime originally designed to keep the men and women of the force fit in a quick way without gym equipment.