What Does the 1:1 Diet Consist Of? A Complete Guide

January 3, 2026 •

5 min read

First launched in the UK in 1984, The 1:1 Diet, originally known as the Cambridge Diet, has evolved to help millions achieve their weight loss goals. This structured plan combines a range of nutritionally complete meal replacement products with personalized guidance from a dedicated consultant. It is important to note this is different from the '1:1:1 diet' philosophy, which is focused on balancing meals with one protein, one carbohydrate, and one fat.

Quick Summary

The 1:1 Diet is a six-step program that utilizes nutritionally complete meal replacement products, combined with personalized consultant support, to promote weight loss.

Key Points

Structured Plan: The 1:1 Diet follows a six-step program, progressing from very low-calorie meal replacements to a maintenance phase with conventional food.
Meal Replacements: It consists of proprietary shakes, soups, bars, and other products that are nutritionally complete but low in calories.
Personal Support: A key component is the one-to-one guidance and motivation provided by a dedicated diet consultant.
Induces Ketosis: The initial restrictive steps can put the body into a state of ketosis, which can lead to rapid weight loss by burning fat.
Flexibility: The multi-step system allows for a personalized approach, with options for different daily calorie totals as you move through the plan.
Potential Side Effects: The initial, very low-calorie stage can cause side effects like headaches, fatigue, and constipation.
Long-Term Focus: The final steps are designed to help dieters transition back to conventional food and maintain their weight loss for the long term.

Understanding the Core Components of The 1:1 Diet

At its heart, The 1:1 Diet by Cambridge Weight Plan is built upon two foundational elements: a range of calorie-controlled, nutritionally complete meal replacement products and personalized, one-to-one support from a trained consultant. The diet is structured into six flexible 'Steps' that cater to individual needs and lifestyle, progressively moving from a very-low-calorie diet (VLCD) to long-term weight maintenance. This contrasts with the separate and distinct '1:1:1 diet' philosophy, which promotes eating one portion of protein, one of carbs, and one of fat at each meal. The official 1:1 Diet is a carefully researched program with a history of development by nutritional experts.

The Role of Meal Replacement Products

A key aspect of the diet is the use of specially formulated products designed to provide all the essential vitamins and minerals your body needs while keeping calories low. This wide range of products helps prevent nutritional deficiencies that can occur with extreme calorie restriction on conventional food plans. These products come in a variety of formats to prevent boredom and address different cravings.

Common product categories include:

Shakes and smoothies: These offer a quick and convenient option for any meal, with a variety of flavours like chocolate, vanilla, and various fruits.
Soups: Hearty and warming soups, such as chicken and mushroom or vegetable with croutons, provide a savoury meal option.
Bars and Bites: These are perfect for snacking on the go and include options like peanut crispy bars and salted caramel bites.
Porridge and Cereals: For a comforting breakfast, dieters can choose from flavours like golden syrup or apple and cinnamon porridge.
Savoury meals: Ready-made meals like spaghetti bolognese, chicken tikka curry, and macaroni cheese are also available.

The Importance of a Personal Consultant

Unlike many DIY diets, The 1:1 Diet includes personalized one-to-one support. A consultant, often a person who has successfully completed the diet themselves, acts as a coach, motivator, and guide throughout your entire weight loss journey. They help you select the most suitable products and guide you through the different weight loss and management steps. This consistent, personal support is a significant differentiator and is credited with helping to increase success rates.

How the Six-Step Plan Works

The 1:1 Diet uses a phased approach, consisting of six flexible steps that allow for customization based on your goals and lifestyle.

Step 1: The starting point for many, this is the most calorie-restrictive phase, where all conventional food is replaced with 3-4 meal replacement products daily, resulting in 440 to 800 calories per day. This puts the body into a state of ketosis, where it burns stored fat for energy. Gentle walking is the only recommended exercise during this phase.
Step 2: Combines 3 meal replacement products with a healthy, 200-calorie meal of the dieter's choice.
Step 3: Dieters enjoy 2 meal replacement products alongside a healthy breakfast, lunch, and dinner, with some freedom to plan meals.
Step 4: Increases calories further, adding an extra snack to the meal replacements and conventional meals.
Step 5: Focuses on developing healthy eating habits for portion control and healthy food choices, while still incorporating one meal replacement product.
Step 6 (Maintenance): This is the final stage, where the focus shifts to long-term weight management. The dieter eats a healthy, balanced diet, potentially with some products kept on hand for busy days.

Comparison of Diet Steps


Feature	Step 1 (Sole Source)	Step 3 (Combination)	Step 6 (Maintenance)
Daily Calorie Intake	440-800 kcal	Approximately 1000 kcal	Individualized, around 1200+ kcal
Meal Replacements	3-4 products daily	2 products daily	Optional, for convenience
Conventional Food	None	Healthy breakfast, lunch, and dinner	Healthy, balanced diet
Support Level	Regular check-ins with consultant	Regular check-ins with consultant	Ongoing consultant support
Primary Focus	Rapid weight loss	Gradual reintroduction of food	Long-term weight management

Addressing the Pros and Cons

Potential Benefits

Structured and Simple: The clear, step-by-step approach simplifies weight loss by removing guesswork about food choices and calorie counting.
Rapid Weight Loss: The very-low-calorie initial stages can lead to quick results, which can be highly motivating.
Personal Support: The one-to-one consultant model provides accountability and motivation that many people find crucial for success.
Nutritionally Complete: Products are formulated to provide all necessary nutrients, avoiding deficiencies common with other restrictive diets.

Potential Drawbacks

Restrictive Nature: The initial phases are very restrictive and can be difficult to adhere to for some individuals, leading to potential boredom.
Side Effects: Some people experience side effects like headaches, dizziness, constipation, or feeling cold, especially during the initial VLCD phase.
Sustainability Concerns: Critics suggest that relying on meal replacements does not adequately teach sustainable long-term eating habits, which can lead to weight regain.
Cost: The products and consultant fees can be an expensive investment compared to a conventional diet plan.
Qualifications: While supportive, consultants are not required to be qualified nutritionists.

Who is the 1:1 Diet For?

The 1:1 Diet is designed for individuals with a BMI over 20 who are committed to a structured plan with personal support. It is not suitable for everyone, including those who are pregnant or breastfeeding, children, and those with certain medical conditions. Always consult with a doctor before beginning any restrictive weight loss program. The step-by-step approach is particularly suited for those who need a clear, defined path with consistent support rather than a more flexible, self-directed diet.

Conclusion: Making an Informed Decision

For those wondering what the 1:1 diet consists of, it is a comprehensive, multi-step program that combines proprietary meal replacement products with personalized consultant support to achieve and maintain weight loss. It offers a highly structured approach that can lead to rapid initial results, making it appealing for those who need a kickstart to their journey. However, the program's restrictive initial phases and reliance on specific products mean it requires a significant financial commitment and a high degree of adherence. Long-term success ultimately depends on effectively transitioning through the later steps and developing sustainable, healthy eating patterns with the help of the consultant. For anyone considering this path, understanding the full commitment required, including potential side effects and costs, is essential. The personalized support sets it apart, but it is not a one-size-fits-all solution for weight management.

Visit the official 1:1 Diet Website for more information about their program and products

Frequently Asked Questions

The 1:1 Diet was formerly known as the Cambridge Diet or Cambridge Weight Plan. It was first launched in the UK in 1984 and was later rebranded to emphasize the personalized, one-to-one support from consultants.

Yes, The 1:1 Diet products are formulated by nutritional experts and are designed to provide a balanced intake of vitamins and minerals, even during the most restrictive stages of the diet.

While in-person consultations are available, many consultants now offer virtual support via phone or online communication, providing flexibility for dieters.

The initial, low-calorie phases can cause feelings of hunger as your body adjusts. However, the products are formulated to be as satisfying as possible, and many people report reduced hunger as they enter ketosis.

The diet consists of a wide range of branded meal replacement products, including shakes, soups, bars, smoothies, porridge, and pre-prepared meals. Conventional food is gradually reintroduced in the later steps.

The diet is structured with long-term weight maintenance in mind. The final steps focus on transitioning to conventional food and developing sustainable healthy eating habits.

During the very-low-calorie phases, some people may experience side effects such as headaches, dizziness, fatigue, and constipation. These symptoms often improve as the body adjusts.

The 1:1 Diet (by Cambridge Weight Plan) is a meal replacement program with consultant support. The separate '1:1:1 diet' is a different approach, focused on balancing meals with one portion of protein, one of carbohydrate, and one of fat, without specific products.

No, the one-to-one support from a personal consultant is a fundamental part of the program. They are there to guide you through the steps and provide accountability.