It works on several 'steps' or levels of diet. If you are heavily overweight (they say a BMI of over 25 at least) and have found that diets haven't worked for you in the past, then you will want to start at stage one.
This is called Sole Source, named after the meal-replacement products you'll be eating, and includes around four Cambridge products a day, coupled with 2.5 litres of water.
Price-wise it costs about £44 a week, which they say is cheaper than Weight Watchers.
We wanted to find out if it really worked, and what the challenges and benefits were, so HuffPost UK Lifestyle spoke to slimmer Cacia Griggs who works as a sales and marketing team leader, who managed the feat of going from a size 24 to a size 10 in 18 months.
She said: "I started the diet in July 2011 and as with anyone who is overweight, there were lots of reasons why I wanted to lose the weight. But, I would lose motivation because I wouldn't see the results quickly and I had 8 stone to lose.
"The final straw was when I saw an article that said if the parents were obese, then the children of the same sex are likely to become obese. I could not imagine my daughter Isabelle, who was three at the time being obese. Something had to change. People in my office had done the diet before and recommended it."
Once you sign up, you're assigned a consultant - and this person is quite critical to the success of your plan as they are the ones that keep you on track, and are your support when things seem impossible. "I found it invaluable," says Cacia, "because when you're having a day when you don't feel so motivated, it helps a lot. There were of course occasions when I had a wobble, but after you've indulged your cravings, the feeling you get afterwards is not good - you feel sluggish and it isn't worth it."
The reason for the dramatic weightloss is because, Kerensa Preedy-Houston at Cambridge Weight Plan (CWP) says, "When you start step one, your body goes into ketosis."
Ketosis, says Medical News Today, is when "the body switches from being a carbohydrate-burning organism into a fat-burning one. The fat stores become a primary energy source, and the person loses weight."
Although replacing a balanced meal with shakes and bars may sound ominous, the meal replacements are stuffed with the vitamins you need to stay healthy - such as boosting your immune system, strong nails and teeth, and energy levels, but for anyone, moving from a diet of regular food to such extreme diet food can be a challenge. "
The diet pushes your body into a state of ketosis, but the problem is that some experts are not convinced it is a healthy state for the body to be in.
However, on the diet, the maximum length of time you can be on the Sole Source is 12 weeks. Be prepared for some side effects - reported symptoms include bad breath, dizziness and nausea.
Blogger Laura Summers, who wrote positively about the diet, said that she did find the bad breath a challenge and that you need to be prepared to give up caffeine.
However, if you are in it for long term weight management then you can choose a more gentle plan with an allowance of 1,500 calories a day - you can combine the specially-formulated bars, drinks, soups and porridge along with other 'regular' food.
Although I'm normally suspicious about dramatic weight loss diets, I am impressed that the Cambridge Weight Plan is quite transparent about what some of the health complications might be.
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Kerensa added: "CWP is generally very well tolerated but some customers do experience side effects. For example we have noted cases of gallstones but we should note that people who are overweight or obese may also experience gallstones.
"Gout is another condition that we have seen. This is because when people lose weight the level of uric acid increases and so does the risk of gout."
The NHS says that it does not think the CWP is sustainable in the long term, but that it can help with the initial bulk of losing weight. For a lot of people who are obese, this can be the initial challenge - often the reason why dieting falls by the wayside is because it takes so long for weightloss to make itself evident on an overweight person.
Cacia used to be a size 24 (but did describe herself as probably being a 26), and didn't get exercise, or control her diet. She said: "Everything was effort, even just going for a lunchtime walk. I’d be panting and puffing and wish I hadn’t done it. With food, we now have takeaways maybe once a month if that but we used to have maybe two a week.
"Because I didn’t have anything I was bothered about maintaining, there was nothing I wanted to maintain. I didn’t care about what I was eating. At dinner, I'd have all the wrong stuff: chips and chocolate. At work, if there were snacks handed around – I’d be the first one at them. Another thing I did an awful lot is that I would eat something while cooking. So by the time dinner was ready, I probably wasn't hungry, but I'd eat it anyway because I'd cooked it."
Exercise is something that is not advised while on step one because the body is taking time to adjust to the reduced calorie intake. And, advises CWP, visit your GP before embarking on the diet. "Exercise is something that could be discussed during their appointment, especially if normally inactive," Kerensa says.
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Fat Makes You Fat
<strong>Why that's BS: </strong> It depends on the type of fats you're eating, says Tricia Psota, RD, a nutritionist based in Washington D.C. "Fats in chips, cookies, and greasy foods can increase cholesterol and your risk for certain diseases. But good fats, like nuts, avocados and salmon, protect your heart and support your overall health." And when paired with a healthy diet, the right fats can help keep you from being, well, fat, adds Sharon Palmer, RD, author of The Plant-Powered Diet.
Stop Snacking To Lose Weight
<strong>Why that's BS:</strong> Eating in small, frequent amounts is a great way to curb hunger, control portion sizes, and make better nutritional choices, says Mike Clancy, CDN, a personal trainer at David Barton's Gym in New York City. "Smarter snacks like nuts, fruits, and yogurt will keep your energy levels high throughout the day." (Need proof? Our 400 Calorie Fix plan -- which involves three or four meals plus snacks -- can help you lose 11 pounds in just two weeks!)
A Calorie Is A Calorie -- And You Should Count Them
<strong>Why that's BS:</strong> "Not all calories are the same," says Clancy. "The type of calories, the timing of the calories, and the quality of the calories can significantly alter the effect of the calories on the body," he says. "Food creates reactions within our bodies and the type of food you eat is an important component in diets." For example, 50 calories of an apple will cause a different internal reaction than 50 calories of cheesecake, says Clancy. "The quality of the calories is also important because the chemicals, hormones, and general byproducts that are found within processed food effects the absorption of real nutrients." Quality calories are nutrient dense, like spinach. Calories that don't contain any nutrients -- also known as "empty" calories -- are like the ones found in French fries. Bottom line: Calories are important for understanding portion control, but they’re not the only factor in good nutrition, says Clancy.
Cut Out Carbs
<strong>Why that's BS:</strong> The research on carbohydrate intake is often misinterpreted, says Chrissy Carroll, MPH, RD, founder of Inspired Wellness Solutions, LLC. "Yes, it is true that excessive intakes of refined carbohydrates, like white bread or white rice, may lead to weight gain or increased cardiovascular risk. But there is no research suggesting that healthy carbohydrates, such as whole grains, fruits, vegetables, or legumes, can negatively impact health or weight. On the contrary, many studies suggest a diet high in these plant-based foods is associated with better overall health." Case in point: A 2002 American College of Nutrition study that found replacing refined grains with whole-grain and minimally processed grain products, along with increasing the intake of fruits and veggies, can help lower dietary glycemic load and insulin demand. This, in turn, can ultimately reduce the risk of both type 2 diabetes and heart disease, says Kristin Kirkpatrick, MS, RD, manager of wellness nutrition services for the Cleveland Clinic Wellness Institute. So, keep the carbs! And aim for those that come from 100% whole grains or fruits, adds Kirkpatrick.
Load Up On Protein
<strong>Why that's BS: </strong>Sorry, caveman lovers: eating lots of protein is not the key to healthy weight loss. Why? The body needs three macronutrients: Protein, carbohydrates, and fat, says Rania Batayneh, MPH, a nutritionist and author of the forthcoming The One One One Diet (published by Rodale, which also publishes Prevention), and focusing exclusively on protein for weight loss makes no sense. "You not only deprive your body of fiber and other antioxidants found in healthy carbohydrates -- whole grains, fruits, and veggies -- but you also run the risk of eating too much fat in your diet which can lead to high cholesterol and triglycerides.”
Go Gluten-Free To Lose Weight
<strong>Why that's BS: </strong>There's no scientific evidence that gluten is a particularly fattening ingredient, says Palmer. "The problem is that we eat too many refined grains -- foods made of white flour or other refined grains," she says. And cutting gluten without checking with your doctor first can lead to deficiencies in important nutrients, such as fiber, iron, vitamin B12 and magnesium, says MaryAnne Metzak, CDN, a nutritionist in Southampton, NY. In the meantime, focus on getting healthy whole grains in moderate portions.
You Burn More Calories Working Out On An Empty Stomach
<strong>Why that's BS:</strong> Working out with or without food in your stomach doesn't affect calorie burn -- but skipping meals before sweat sessions may result in muscle loss, finds a study published in the Strength and Conditioning Journal. And before you settle for a sports drink, know this: While a quick sip of sugar energizes your muscles, the drink’s other artificial additives can be harmful to your health, says Sanda Moldovan, DDS, MS, CNS, a diplomat of the American Academy of Periodontology. Instead, go for naturally sweet fruit, like bananas, peaches, and mangos before your sweat session. Or try an ounce of dark chocolate for the same caffeine fix you get from a half cup of coffee. "Chocolate also contains feel-good substances, called neurotransmitters, which are the same release during a 'runner's high,' " says Moldovan.
Eat Every Two Hours To Rev Your Metabolism
<strong>Why that's BS:</strong> Going four or five (or even eight!) hours between normally-sized meals will not make your metabolism slow down, says Monica Reinagel, MS, a nutritionist based in Baltimore. "Eating more frequently may help stave off hunger, which can help you fight temptation. But if you want to do this, you have to be careful to keep your meals and snacks really small," she says. "Otherwise, eating every 2 hours can simply lead to taking in too many calories over the course of the day."
Watch What You Eat During The Week, But Take The Weekends Off
<strong>Why that's BS: </strong>Throwing caution to the wind on the weekends can offset the consistency and success you had all week, says Batayneh. "On the weekends, we tend to sleep in, maybe missing our workout, typically drink more alcohol and have heavier meals. So if you lose about one pound between Monday and Friday, you just might gain it back -- or at least maintain it, really taking away the efforts towards weight loss." Which means if you're trying to lose weight, the weekends shouldn't be a free-for-all. You still need a plan, says Batayneh. Some suggestions: passing on the bread basket and limiting yourself to one cocktail.
Swear Off Forbidden Foods
<strong>Why that's BS:</strong> "We tend to be in 'all or nothing' mode when we diet and never seem to find a middle ground," says Batayneh. "You have to realize that you can’t have pizza, French fries, and chocolate cake all in the same day, but -- with careful planning -- you can enjoy these foods when they are presented to you. Just don’t go for seconds and share if you can." In fact, research shows that moderately indulging in "forbidden foods" is what keeps people from bingeing on the stuff.
What is the first week like? Cacia says: "It was quite hard, everyone has different side effects, and for me, getting used to drinking a lot of water was difficult considering I used to drink zero water. I craved a lot but once the first week was out of the way, it got easier and I had lost 10 pounds and that was enough motivation to keep going. In the past it has taken me four weeks to lose ten pounds."
Cacia would try and motivate herself with various methods such as buying a dress one size too small that she knew she would soon get into if she kept with the diet. She started to chew gum when she was baking, and to avoid picking at leftovers, she'd sprinkle pepper over them, as she didn't like the taste of it.
One of the most difficult aspects of the diet however, is that because you're replacing all meals with shakes and diet products, it makes eating out and socialising tricky. "I avoided going to restaurants altogether," she said.
But there is light at the end of the tunnel, specifically, step two when you can introduce food into the diet. "I used a small plate which I found helped a lot. That way, you don't feel the need to fill up the plate."
So what's the conclusion? If we are to go by Cacia's testimony, then the diet is a results-driven godsend for people struggling with obesity, but there is no question that it requires a lot of willpower and you will need the support of people around you. Especially since we live in a culture of 'oh go on, one won't hurt you' which can apply to everything from doughnuts to an extra pint in the pub.
"There are people who don’t understand, and have never had a weight problem and these are the people who may unknowingly sabotage your diet," she says. "The first few months were most difficult, and a large part of my job is events so we go out with customers and as a team. I had to avoid them. Once I had done the diet for a few months, I felt in a much stronger place.
"When people notice your weight loss, the support is incredible – it was amazing. Also, I did go on the CWP social media sites and the motivation on there from people keeps you on track and reminds you why you’re doing it."
To contact a consultant at Cambridge Weight Plan, visit the website.