Origins and Principles of The Fast 800
The Fast 800 diet was developed by the late medical journalist Dr. Michael Mosley, who first gained prominence for popularizing intermittent fasting with his 5:2 diet. After reversing his own type 2 diabetes through dietary changes, Mosley and his team launched the Fast 800 to help others achieve similar health benefits. The diet is founded on the principles of a low-carbohydrate, Mediterranean-style eating plan, which is widely regarded as one of the healthiest dietary patterns. The Fast 800 is not a single, long-term 800-calorie regimen but a flexible program with three distinct phases designed to aid weight loss and improve metabolic health.
The Three Phases of the Fast 800 Diet
Mosley's program offers a flexible, phased approach to suit different weight loss goals and lifestyles.
- The Very Fast 800 (Rapid Weight Loss): This intensive phase involves consuming approximately 800 calories per day, focusing on nutritious, moderately low-carb, Mediterranean-style recipes. It is typically followed for 2 to 12 weeks, and only under medical supervision, for individuals with significant weight to lose or those with type 2 diabetes. The goal is to induce a "metabolic switch," where the body begins burning fat for fuel after depleting its sugar stores.
- The New 5:2 (Gradual Weight Loss): For a more gradual approach or as a transition from the intensive phase, this method involves consuming 800 calories on two non-consecutive days of the week. On the other five days, individuals eat sensible, moderately low-carb, Mediterranean-style meals without strict calorie counting.
- The Way of Life (Maintenance): This is the final, long-term phase for maintaining a healthy weight and lifestyle indefinitely. It involves following the principles of a Mediterranean-style diet without calorie counting or fasting days, focusing on wholesome, unprocessed foods.
How the 800-Calorie Phase Works
The core mechanism of the intensive 800-calorie phase is the process of metabolic switching. By severely restricting calorie and carbohydrate intake, the body is forced to use its stored fat for energy instead of relying on glucose from carbohydrates. This metabolic state, known as ketosis, is what drives rapid weight loss and can lead to improved blood sugar control. To achieve this, the diet emphasizes specific nutrient-dense foods:
- High-quality protein: Lean meats, fish, eggs, and tofu help preserve muscle mass and promote satiety.
- Healthy fats: Sources like olive oil, nuts, and seeds provide essential fatty acids and increase fullness.
- Fiber-rich vegetables: Non-starchy vegetables provide vital nutrients and fiber, aiding digestion and reducing cravings.
Benefits and Risks of the 800-Calorie Diet
| Feature | Benefits | Risks |
|---|---|---|
| Weight Loss | Can lead to rapid, clinically significant weight loss in the short term, averaging 8.7kg at 12 months for those with BMI ≥ 30. | Higher likelihood of rapid weight regain after stopping the restrictive phase. |
| Metabolic Health | Evidence from studies like DiRECT and DROPLET shows potential for type 2 diabetes remission and significantly improved blood sugar control. | Potential for nutritional deficiencies if not carefully planned or if using inadequate shakes. |
| Sustainability | The program's multi-phase approach aims for long-term lifestyle changes and weight maintenance. | The intensive 800-calorie phase can be difficult to stick to due to side effects like fatigue, headaches, or irritability. |
| Suitability | Particularly effective for those with obesity or type 2 diabetes who need to lose a lot of weight quickly. | Not suitable for pregnant or breastfeeding women, children, teenagers, or individuals with a history of eating disorders or certain medical conditions. |
A Balanced Approach to Fasting and Health
While the intensive 800-calorie phase is effective for jumpstarting weight loss, Mosley’s full Fast 800 program is designed to be a long-term, sustainable lifestyle. The shift to the New 5:2 and Way of Life phases is crucial for preventing weight regain and embedding healthy habits.
- The program emphasizes a low-carb, Mediterranean-style diet, which has been shown to improve cardiovascular health, cognitive function, and gut health.
- It encourages mindfulness and behavioral changes to foster a healthier relationship with food.
- Exercise, including high-intensity interval training (HIIT), resistance training, and incidental exercise, is an integral part of the program to boost metabolic health.
It is important to note that very low-calorie diets (VLCDs) are not suitable for everyone and require careful consideration and medical consultation. For individuals with a history of eating disorders, VLCDs can be particularly dangerous and should be avoided. The ultimate goal is not just rapid weight loss, but a sustainable change towards a healthier way of life.
Considerations for Starting the Fast 800
Before embarking on the Very Fast 800, consulting a healthcare professional is strongly recommended, especially if you have existing health conditions or are on medication. This ensures the diet is safe and appropriate for your individual needs. The program’s emphasis on real food, complemented by shakes for convenience, ensures nutrient intake is maximized during the restrictive phase. The long-term success hinges on transitioning to a sustainable eating pattern like the New 5:2 or Way of Life, which promote balanced nutrition and gradual, lasting weight management. More information on intermittent fasting can be found on reputable health sites like Johns Hopkins Medicine, which provides detailed guides on different fasting methods.
Conclusion
Michael Mosley's 800 calorie diet, part of the larger Fast 800 program, offers a structured and evidence-based approach to rapid weight loss and metabolic improvement. By combining intermittent fasting with a low-carb, Mediterranean-style diet, it aims to achieve significant health benefits, including potential type 2 diabetes remission. However, the intensive phase is a short-term tool, and long-term success depends on a gradual transition to more sustainable eating habits. As with any restrictive diet, medical supervision is crucial to ensure safety and effectiveness. The program's holistic approach to lifestyle, exercise, and mindfulness sets it apart from simple crash diets, offering a potential path to lasting wellness for suitable individuals.
