19th September 2025

The Basic Rules of The Fast 800 Diet

The Fast 800 diet, created by Dr Michael Mosley, is a flexible programme that progresses through several stages, beginning with a rapid weight loss phase and moving through to a sustainable long-term eating pattern.

Depending on your goal, you can choose whether to start at phase one of the diet and rapidly kickstart weight loss, or you can enter at the maintenance phase. The Fast 800 diet phases include The Very Fast 800 which aids rapid weight loss, The New 5:2 which is aimed at gradual weight loss through intermittent fasting, and the Way of Life diet that supports weight maintenance and general overall health.

One of the basic rules of The Fast 800 diet is that all the approaches are based around the principles of a Mediterranean-style diet, which has been shown to be one of the healthiest eating patterns on the planet. Rich in protein, fibre and healthy fats, it’s a low-carb diet that promotes physical health and mental wellbeing.

Just keep reading to learn the basic rules of The Fast 800 diet, or sign up to the programme here to find out more.

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What are the basic rules of The Fast 800 diet?

  • The Very Fast 800: This diet is for those with significant weight to lose, or for those who are aiming to lower blood sugar and reverse type 2 diabetes. It’s a short-term, rapid weight loss approach that involves consuming 800 calories per day for up to 12-weeks.
  • The New 5:2: This intermittent fasting diet is for those who are aiming to maintain their weight or lose weight gradually. It involves fasting (consuming 800 calories) two days a week, and eating sensible portions the remaining five days without the need for calorie counting.
  • Way of Life: This approach can be followed for life, and involves no calorie restriction, just nutritious food that supports optimal health and weight maintenance. We encourage exercise sensible portions of Mediterranean-style meals to maintain your target weight once that has been achieved, and continually improve metabolic health.

How long can I follow it for?

Once you’ve determined which approach is right for you, one of the basic rules of The Fast 800 diets is following it for the right amount of time. The Very Fast 800 or The Fast 800 Keto should be followed for a minimum of two weeks and a maximum of 12 weeks, or until a healthy BMI (> 25) has been achieved, whichever comes first. The Way of Life and The New 5:2 diets can be followed indefinitely as they are more of a lifestyle than a short-term diet.

The Fast 800 diet core principles

The Fast 800 is about so much more than just food. One of the basic rules of The Fast 800 diet is to approach a health transformation from a holistic perspective. This means that in order to be as happy and healthy as you can be, you must address all aspects of your health, not just what you eat.

A healthy body and mind needs more than just nutritious food to thrive, which is why we incorporate many other key aspects of health in our programme, including:

  • Exercise: Our Programme includes guided workouts catering to different abilities and fitness levels, including high-intensity interval training (HIIT), resistance training and low-impact workouts like Pilates and yoga.
  • Behaviour Change: The Fast 800 Behaviour Change course helps you develop new healthy habits and stick to them.
  • Mindfulness: Mindfulness is a powerful tool when it comes to mental and physical wellbeing. Our programme includes guided meditations and mindfulness resources to support any health journey.
  • Knowledge: One of the basic rules of The Fast 800 diet is that everything we do is based on science. We share the tools and knowledge you need to succeed in your journey through articles both online and on our programme.
  • Community: We know the power of community when it comes to weight loss, so our programme gives you access to an exclusive cohort of other members you can connect with on your journey, along with topical forums for additional support relevant to you.

How to get started

Now you know the basic rules of The Fast 800 diet, get started with your 7-day free trial of our Programme. There you’ll find over 900 Mediterranean-style recipes, helpful meal plans, expert-led workout videos, mindfulness resources and so much more to help guide you through your health journey towards your best self.

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