Cambridge Diet Guide: Probing Rapid Weight Loss Promises

Is this rapid weight-loss plan right for you? Keep reading to find out.

The Cambridge diet is an example of an extreme weight loss diet that might be recommended to someone who needs to lose weight quickly for medical reasons.

Its branded products aim to provide the nutrients you need while severely restricting your calorie intake to provide fast results.

But what does the Cambridge diet entail, exactly?

In this weight loss guide, we will give you everything you need to know about what the Cambridge diet involves, how to follow it, and the pros and cons of the Cambridge diet for weight loss and health.

Let’s jump in!

A nutritionist helping a patient.

What Is the Cambridge Diet Plan?

The Cambridge diet plan has recently been renamed the 1:1 diet.

So, any references to the Cambridge diet essentially refer to the 1:1 diet, as these terms can still be used somewhat interchangeably.

The Cambridge diet plan is a very low-calorie weight loss diet designed for rapid and significant weight loss.

The 1:1 diet meal plan uses meal replacement products with specialty weight loss diet shakes, weight loss diet bars, weight loss pudding and porridge, and other weight loss replacement products instead of real food. 

The engineered diet foods are intended to provide the nutrients you need to eat in a day while rigidly controlling calories to support drastic and quick weight loss.

Owing to the original name of the Cambridge diet, the plan was first developed by a doctor at Cambridge University in 1970 named Dr. Alan Howard to help patients dealing with obesity lose weight.

While this diet was originally used only in clinical settings, it became a commercial product or commercial diet program in the US in 1980 and in the UK in 1984.

In recent years, it has rebranded to become the 1:1 diet plan to emphasize the one-to-one relationship between the dieter and their personal diet consultant.

A nutritionist helping a patient.

How Does the Cambridge Diet Work?

This diet is a very low-calorie and low-carb diet for weight loss and potentially to reverse diabetes

There are approximately 35 Cambridge diet food products, including weight-loss shakes, soups, porridge, and bars. 

It has a similar effect on the body as the keto diet in that due to the insufficient carbohydrate intake on the diet to support energy needs, the body shifts into a state of metabolic ketosis on the 1:1 diet meal plan.

Ketosis occurs when your body has to burn body fat for fuel. This creates ketone bodies in the liver, which can then be metabolized for energy.

There are six levels or versions of the Cambridge diet plan.

Depending on the level, the Cambridge diet meal plan only provides 450 calories to 1500 calories per day.

The diet starts very extreme to induce rapid weight loss and gradually becomes a little more flexible.

Packaged granola bars.

There are six Cambridge diet plan steps:

#1: Sole Source

Step 1 is the most extreme Cambridge diet weight loss meal plan that will leave you in a severe calorie deficit.

You consume 3 to 4 Cambridge Diet meal products per day for 1 to 12 weeks. The Cambridge Diet Sole Source plan only provides 415-554 calories per day.

#2: Sole Source +

In the Cambridge diet Sole Source+ plan, you eat 3 Cambridge Diet meal products and 200 ml of skim milk per day for 1 to 12 weeks.

Cambridge Diet Sole Source+ plan only provides about 615 calories per day.

#3: Step 2

For the Cambridge Diet Step 2 meal plan, you eat two servings of Cambridge Diet meal products along with high-protein foods, skimmed milk, and some non-starchy vegetables.

The number of calories on this meal plan is only 810 calories per day and must be followed for at least one week with no maximum duration.

Packaged foods.

#3: Step 3

For the Cambridge Diet Step 3 plan, you eat two Cambridge Diet meal products, skim milk, a low-calorie meal for breakfast, and salads for lunch and dinner.

The Cambridge Diet Step 3 meal plan provides only 1000 calories per day and must be followed for at least two weeks. 

#4: Step 4

By Step 4, you can follow the same plan as the previous step, but you now have more options for lunch and dinner. This step is followed for two weeks.

#5: Step 5

For the Cambridge Diet Step 5, you drop down to 1 Cambridge Diet meal product plus skim milk, breakfast, lunch, dinner, and now also a snack. This step is followed for two weeks.

#6: Maintenance

Once you’ve reached your goal weight, you follow the Maintenance Cambridge Diet.

This is intended to be a lifelong plan where you can consume however many Cambridge diet products you want, along with calorie-controlled foods according to your caloric needs.

A person eating a salad.

Some people jump right in with the Cambridge Diet Sole Source and then work all the way through to the maintenance phase in a stepwise manner, while others start at a higher step if their weight loss goals are less extreme or they have higher caloric needs.

If you go through all six steps, the Cambridge diet program takes 12 weeks in most cases.

The Cambridge diet foods are said to be nutritionally balanced and provide no more than 200 cal. Each Cambridge diet meal replacement product costs roughly £2.78, which can certainly add up quickly.

Is the Cambridge Diet Good for Weight Loss and Health?

There are several potential benefits, given the important disclaimer that the Cambridge diet should only be followed if you indeed have a significant amount of weight to lose and a trustworthy doctor has referred you to try this diet program for weight loss. 

Here are some of the benefits:

  • The food products are said to be nutritionally balanced.
  • Dieters work with a counselor through the program.
  • Some scientific studies have found that very low-calorie diets can be followed for safe and effective weight loss and maintenance.
  • In addition to being a weight loss diet plan, some patients have had success stories following this diet program for reversing health conditions such as hypertension, pre-diabetes, type 2 diabetes, obstructive sleep apnea, obesity, osteoarthritis, and atherosclerosis.1Christensen, P., Meinert Larsen, T., Westerterp-Plantenga, M., Macdonald, I., Martinez, J. A., Handjiev, S., Poppitt, S., Hansen, S., Ritz, C., Astrup, A., Pastor-Sanz, L., Sandø-Pedersen, F., Pietiläinen, K. H., Sundvall, J., Drummen, M., Taylor, M. A., Navas-Carretero, S., Handjieva-Darlenska, T., Brodie, S., & Silvestre, M. P. (2018). Men and women respond differently to rapid weight loss: Metabolic outcomes of a multi-centre intervention study after a low-energy diet in 2500 overweight, individuals with pre-diabetes (PREVIEW). Diabetes, Obesity and Metabolism20(12), 2840–2851.
  • Prepared foods mean you do not need to cook or prepare meals.
A person opening a box of prepped foods.

While there are some medical implications where the 1:1 diet weight loss plan can be effective and safe, there are also drawbacks:

  • Diets that provide fewer than 1000 calories a day should generally not be followed for more than 8 to 12 weeks at most, even under the guidance of a medical team.2Leeds, A. R. (2014). Formula food-reducing diets: A new evidence-based addition to the weight management tool box. Nutrition Bulletin39(3), 238–246.
  • Extreme caloric restriction can put the body in starvation mode, decreasing your metabolic rate through a process called adaptive thermogenesis.3Schwartz, A., & Doucet, É. (2009). Relative changes in resting energy expenditure during weight loss: a systematic review. Obesity Reviews11(7), 531–547.
  • You may also lose lean body mass, making it difficult to continue losing weight over time.4Schwartz, A., & Doucet, É. (2009). Relative changes in resting energy expenditure during weight loss: a systematic review. Obesity Reviews11(7), 531–547.
  • All of the 1:1 diet foods are bioengineered and are not “real food.“ This meal replacement diet can make it difficult to transition back to regular eating once you are off this weight loss programme, and studies suggest that eating whole, natural foods is much better for your health than ultra-processed foods.
  • It is very expensive.
  • Extreme weight loss diets can cause a myriad of side effects, such as constipation, flatulence, mood swings, nausea, bad breath, cold sensation, fatigue, hair loss, dizziness, and even gallbladder stones.
  • The diet may trigger eating disorders or a dysfunctional relationship with food.
  • Limited food products can cause boredom.
  • Generally followed for the short term and not a sustainable weight loss diet.
Packaged foods.

Generally, the Cambridge weight plan is not intended for everyday individuals looking to lose weight when they only have 10 to 20 pounds to lose.

It is an extreme weight loss diet and should generally only be followed if guided or recommended by a medical professional.

According to Harvard Health, the minimum calories a day adults should be eating unless otherwise guided by a healthcare professional is 1200 calories a day for a woman and 1500 calories a day for a man.5Publishing, H. H. (n.d.). Calorie counting made easy. Harvard Health.

‌Therefore, the Cambridge Diet will likely not provide everything your body needs and can be dangerous.

Under the new rebranding, the 1:1 diet weight loss program does provide individualized support with a diet counselor.

However, this should not necessarily take the place of seeking advice from your own healthcare provider and nutritionist prior to choosing the Cambridge diet over another less aggressive weight loss diet.

If you are looking for a healthy diet full of delicious and healthy meals, check out our guide to the Mediterranean Diet:


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Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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