Baby food cleanse: Jennifer Aniston
JENNIFER ANISTON
Super-skinny celeb trainer Tracy Anderson is apparently responsible for Jennifer Aniston's latest diet, which has seen her drop half a stone.
Dubbed 'The Baby Food Cleanse', the idea is that throughout the day you consume 14 portions of puréed food.
All the purées are free of oils, spices and salt, and can range from fruit smoothies and oatmeal to soups containing dandelion greens.
In the evening, a normal dinner of lean meat and vegetables is allowed.
Tracy apparently believes that the easier it is for your body to process food, the swifter you'll lose weight.
URSULA SAYS: This seems totally counter-intuitive to me.
If your food is easier to digest, it means the calories are more readily available to your body.
It's the reason why eating an apple actually gives you fewer calories than if you drink the juice of one apple.
STEVE SAYS: Human beings need roughage.
Eating lots of green veg and food that bulks out the bowel prevents bowel cancer, so by liquidising your food, you run pointless and unnecessary risks with your long-term health.
Naomi Campbell: Advocates the Maple Syrup Diet
NAOMI CAMPBELL
Alongside a host of other celebrities - including Beyonce, who used the plan to shed 22lb in ten days - Naomi has admitted to being a fan of the Master Cleanse, also known as The Lemonade or Maple Syrup Diet.
This diet involves drinking between six and 12 glasses a day of a maple syrup, lemon juice, water and cayenne pepper mixture.
She told Oprah last week that she tries to do the cleanse three times a year and the longest that she's ever done it for is 18 days.
She believes it's important to 'clean your body out once in a while'.
URSULA SAYS: If this mixture is all you are consuming, you are going to lose weight because it is an incredibly low-calorie diet, but you're not going to keep the weight off when you stop.
The only way to lose weight that will last is slowly and sensibly.
STEVE SAYS: The human body is brilliant at detoxing itself. The liver and kidneys are all that you need.
To suggest that you need to give your digestive system a break is just nonsense.
Cheryl Cole: Theories behind her Blood Type Diet are unproven
CHERYL COLE
Cheryl insists that she changed her diet to feel better rather than to stay slim, and she's convinced that it has increased her energy levels.
The Blood Type Diet was developed by Peter D'Adamo and is based on the idea that your blood group indicates physiological differences that make certain foods easier for your body to digest.
According to the plan, if you are blood type O, you should follow a high-protein, low-carb diet, cutting out most grains. If you're blood type A, you should eat a mainly vegetarian diet low in fat and high in carbs.
Type Bs should eat a varied diet, including meat and dairy, while type AB can eat most foods recommended for both A and B blood types.
URSULA SAYS: It might sound as if it's rooted in science, but there's no strong evidence to suggest that differences between blood types have a noticeable effect on digestion.
Some people have allergies and sensitivities to certain foods, but there's nothing to suggest that this is related to blood groups.
STEVE SAYS: Cutting entire food groups out of your diet arbitrarily could result in you being deficient in certain essential vitamins and minerals, so a diet like this, which has no credible basis, is not advisable.
Complicated diet plan: Cindy Crawford
CINDY CRAWFORD
The supermodel is a fan of The Zone Diet, when everything you eat is in the ratio of 40 per cent carbohydrates, 30 per cent protein and 30 per cent fat.
The diet bans sugar, bread, pasta, rice, alcohol and caffeine.
It also recommends you restrict high-sugar fruit and vegetables, such as papaya, mango and carrots.
And alongside your three main meals, you have two mini-meals to maintain blood sugar levels.
URSULA SAYS: Three meals and two snacks is a sensible way to eat, as long as it is nutritious.
The diet demands that you keep the proportions for every meal and snack.
Calculating something like this is a bit of a faff if you don't have your own personal chef.
STEVE SAYS: If things are complicated, you're more likely to fall off the wagon.
There are far better ways to spend your time than measuring out exact ratios of food.
Cuts out alcohol: Claudia Schiffer
CLAUDIA SCHIFFER
Unlike many irritating celebs who insist they eat whatever they like, Claudia admits she has to work hard for her body.
She doesn't drink alcohol, steers clear of caffeine and exercises regularly. She doesn't believe in dieting as it messes up your metabolism, but has her own rigid healthy eating plan.
She eats only fruit and vegetables before noon, has a light lunch of salad, vegetables or soup, and for dinner has a chicken or tuna salad, or grilled chicken and steamed veg.
URSULA SAYS: There's something to be said for sticking to a regime rather than yo-yo dieting, as studies in animals suggest that fluctuating weight can have an adverse effect on health.
Cutting out alcohol stops you taking in calories that aren't accompanied by any nutritional benefits.
STEVE SAYS: This isn't a diet I'd advocate for most people because if you're only eating fruit in the mornings, you might not get enough fibre and carbs, and could find your blood sugar levels dropping in the afternoon.
Whole fruit is far preferable to fruit juice - the former provides fibre while the latter is really just sugar.
Strict regime: Heidi Klum
HEIDI KLUM
The supermodel is a fan of a strict regime called the Ultimate New York Body Plan, which she used to get back into catwalk shape six weeks after the birth of her second child.
Alcohol, bread, starchy carbs, caffeine, dairy, sweets, fruit and most fats are totally forbidden. You consume no more than 1,200 calories a day in the form of lean protein, vegetables, and healthy fats, such as flaxseed oil, olive oil, pumpkin seeds and sunflower seeds.
You eat every three hours to boost your metabolism, and you must exercise for 90 minutes a day. The plan is meant to be a two-week kickstart.
To keep her motivated, Heidi apparently photographs herself naked once a week.
URSULA SAYS: On such a calorie restricted diet that's also low in carbs, there's no question that you're going to lose weight and lose fat.
Eating little and often helps keep blood-sugar levels steady, but it's unlikely to boost your metabolic rate significantly.
STEVE SAYS: High-protein, low-carb diets can put a lot of strain on the kidneys, as they have to excrete high concentrations of urea. If someone unknowingly has poor kidney function, this could cause problems.
Dukan diet fan: Gisele Bundchen
GISELE BUNDCHEN
Gisele is a fan of the latest diet from France which is the brainchild of nutritionist, Dr Pierre Dukan.
The four-phase diet starts with the seven-day Attack Stage, which is a stricter version of Atkins and South Beach, where you choose from 72 protein-rich foods.
In the second Weight Loss Stage, you alternate days of the high protein diet with days of a low-carb vegetarian diet. When you reach your target weight, you move to the Consolidation Stage, when you gradually add carbs.
They suggest that for every pound you have lost you stay on this stage for 4.5 days.
Finally, you get to the Stabilisation Stage when you can eat what you want except one day per week when you revert to the Attack Stage.
URSULA SAYS: This sounds very similar to the South Beach diet which has three phases.
It's an appealing formula and you will lose weight in the initial stage.
Cutting your calories one day of the week will keep your weight stable if you have an occasional slip.
STEVE SAYS: It's just not healthy to exclude vegetables and carbs from your diet, even if it's just for one day a week.
Sensible approach: Kate Moss
KATE MOSS
Kate decided to overhaul her health with something she dubbed The Vibrancy Diet.
Based on three sensible meals a day, she kicked off with probiotic yoghurts, fruit and toast and then had two meals of grilled fish, or chicken and veg.
She had lots of iced water to keep her appetite down, and it was also said she ditched beer, wine and champagne and only drank vodka with fresh lemon.
Rumour has it that the plan required her to clean her face with boiled milk.
URSULA SAYS: While some studies suggest that drinking a pint of water before meals can reduce how much you eat, it's not proven in the long-term.
As for probiotics, although they're not going to do you any harm, a recent European review of food labelling rejected every health claim made by foods containing them.
STEVE SAYS: Overall, this looks like a sensible approach to eating. The biggest thing she can do in terms of health is stop smoking.
It has a negative effect on the entire body.
Kale soup and exercise: Gwyneth Paltrow
GWYNETH PALTROW
Tracy Anderson is the brains behind Gwyneth's diet for her movie Ironman 2. This plan includes an exercise regime that includes 45 minutes of cardio, 30 minutes of legs and 30 minutes of arms. She did this every day, to lose her 'extra winter weight'.
It is an intense five-day diet. Breakfast is a protein bar or shake. After a workout you get kale juice, and lunch is grilled chicken and vegetables.
Dinner is turkey kale soup and a salad.
URSULA SAYS: You'll definitely see a difference after five days, but you're unlikely to lose fat.
If you do any diet, the first place the body goes for energy is your glycogen, the form in which the body stores glucose.
Glycogen binds water to it, so when you use up glycogen, you also get rid of stored water, which can make it look like you're losing weight.
As soon as you start eating carbs again, your body replenishes carb stores, and the water you've lost.
STEVE SAYS: Calories aren't a bad thing, especially if you're exercising a lot, and restrictive diets with intensive workouts can make people tired, irritable and ultimately depressed.
