How healthy are those celebrity bodies?

Another hard truth is that some celebs will do just about anything to look a certain way. One well-known actress reportedly took pills to over-stimulate her thyroid gland before shooting a movie where she played a super muscled heroine.

Her six-pack abs were impressive, but they weren’t the result of 200 sit-ups a day, only of a chemically enhanced metabolism.

Another trick some celebs use before major magazine or film shoots is called 'peaking'. Several days before shooting a cover, they cut out all carbs from their diet or they might take glycerol, a diuretic that drains water from under muscles, making them look more bulky and veined. You can rest assured many of them only keep this ultra-ripped look for a few days each month, notes Salzmann.

Others in the spotlight simply follow a low-carb or all-protein diet all the time. You need a certain amount of carbohydrate to process protein properly, and an extreme eating plan puts extra strain on the kidneys and liver, says Salzmann.

Also, when you deprive your body of carbohydrates for more than a few days, byproducts called ketones are produced which can make you feel fatigued and headachy. Although you may initially shed pounds and inches on a restricted diet, you'll soon find energy levels plummet and the plan will be tough to sustain.

Most people who try it, end up in a cycle of yo-yo dieting where they repeatedly lose then gain weight.

The good news is, although you might never be Geri-esque, you can tone and re-shape your body through putting in a few extra hours a week at the gym and following a healthy diet. If you cross train, or vary your workouts so they include cardio, strength training and flexibility components, you can transform your shape.

'Angelina Jolie prepared for her role as Lara Croft in Tomb Raider on a programme of sound nutrition and cross training that included 40-minute maximum workouts for five or six days a week,' says Salzmann. What's more, she fulfilled some of her cardio workouts during three-days-a-week strength training sessions by using resistance to elevate her heart rate.

She combined all these things with kickboxing and yoga classes and was so strong by the time she started shooting the film that she was able to do some of her own stunt work.

So, you can continue to admire Geri's abs and Madonna's arms, as long as emulating them isn't your aim. One act you can follow is a challenging weekly cross training routine. Here's a sample programme:

Monday: Weight training
Tuesday: Running or walking
Wednesday: Rest day
Thursday: Body combat class
Friday: Ashtanga yoga class
Saturday: Swimming
Sunday: Rest day

Of course, to reap the benefits of exercise you'll need to follow a healthy diet as well. Dr Wynnie Chan, resident iVillage nutritionist, advocates basing 50 per cent of your daily calories on carbohydrates, 35 per cent on fat and 15 per cent on protein.