What is The Fast 800 Diet?
Developed by Dr. Michael Mosley, The Fast 800 is a flexible weight-loss and health program based on intermittent fasting, a Mediterranean-style diet, and in its most intensive phase, a very low-calorie intake. It is not a single, one-size-fits-all approach but rather a set of adaptable phases to suit different health goals and lifestyles. The diet has three primary approaches: The Very Fast 800, The New 5:2, and The Way of Life. Each phase is built upon the nutritional principles of a moderately low-carb, Mediterranean-style diet, which emphasizes vegetables, lean protein, healthy fats, and fiber.
The most intensive and controversial phase is The Very Fast 800, which involves consuming 800 calories per day for up to 12 weeks. This is designed for rapid weight loss and is meant for individuals with a significant amount of weight to lose or those with type 2 diabetes. The next phase, The New 5:2, involves two fasting days of 800 calories per week, with sensible eating on the other five days, offering a more gradual weight loss option. Finally, The Way of Life is a maintenance phase that involves no calorie counting but focuses on sustaining healthy Mediterranean eating patterns for the long term.
The Potential Benefits of The Fast 800
For suitable candidates, particularly those who are overweight or obese, The Fast 800 diet has shown promising results in clinical studies and user testimonials. The benefits are primarily linked to the diet's core mechanisms of calorie restriction and intermittent fasting, which can lead to rapid fat loss and improved metabolic health.
Scientific Evidence for Efficacy
- Type 2 Diabetes Remission: The DiRECT trial, a major study that influenced the diet's design, found that 46% of participants on an 800-calorie-a-day diet for several months achieved remission of type 2 diabetes.
- Visceral Fat Loss: The diet has been shown to reduce visceral fat, which is the harmful fat stored around the organs.
- Cardiovascular Health: The emphasis on a Mediterranean-style diet, rich in healthy fats and whole foods, supports improved cardiovascular health and reduced risk of heart disease.
- Improved Mood and Energy: Many participants report increased energy levels and improved mood, often attributed to rapid weight loss and better blood sugar control.
The Significant Risks: Is Fast 800 Bad for You?
While the diet has potential benefits, the intense calorie restriction, especially in The Very Fast 800 phase, is not without risk. For a majority of the population, a prolonged very low-calorie diet can be unhealthy and dangerous.
Health Risks of Very Low Calorie Intake
- Nutrient Deficiencies: Sustaining a diet of only 800 calories a day makes it extremely difficult to meet the body's daily requirements for essential vitamins, minerals, fiber, and protein. The Fast 800 program suggests supplements, but real food is always preferable.
- Side Effects: Common side effects include fatigue, headaches, dizziness, constipation, nausea, and bad breath. More serious side effects, such as gallstones, can occur during periods of rapid weight loss.
- Loss of Muscle Mass: In addition to fat, very restrictive diets can lead to the loss of lean muscle mass if protein intake is not carefully managed.
- Metabolic Slowdown: To conserve energy, the body may slow down its metabolism during a prolonged period of very low calorie intake, which can make sustained weight loss and maintenance more difficult over time.
- Eating Disorder Risk: The diet's restrictive nature may trigger or worsen a poor relationship with food for individuals with a history of disordered eating.
Who Should Avoid The Fast 800?
Medical experts, including the diet's own creators, provide a strict list of people for whom the intensive phases of The Fast 800 are not suitable. This includes:
- Individuals under 18 years old
- Pregnant or breastfeeding women
- Anyone who is underweight or has a history of eating disorders
- People with Type 1 diabetes
- Individuals with significant psychiatric disorders or substance abuse issues
- Those with heart abnormalities, uncontrolled heart disease, kidney failure, or who have recently had a heart attack or stroke
- People on certain medications, particularly insulin or blood pressure medication, without strict medical supervision
Comparing The Fast 800 with Standard Diets
| Feature | Fast 800 (Initial Phase) | Conventional Calorie-Restricted Diet |
|---|---|---|
| Calorie Intake | ~800 calories daily for up to 12 weeks. | ~1200-1500+ calories daily, depending on individual needs. |
| Rate of Weight Loss | Rapid and significant, often 10+ kg in a few months. | Gradual and slower, aiming for 1-2 lbs per week. |
| Nutrient Intake | Risk of deficiency is high due to low volume of food, requires careful planning. | Easier to achieve a balanced nutritional intake, less risk of deficiencies. |
| Sustainability | Intensive phase is short-term; reliance is on transitioning to a less restrictive phase for long-term maintenance. | Generally designed for long-term adherence and gradual habit changes. |
| Side Effects | Common side effects include fatigue, headaches, and digestive issues, which typically improve over time. | Side effects are generally milder due to less extreme calorie restriction. |
| Medical Supervision | Strongly recommended due to the intensity and potential risks. | Less commonly required, though always advisable to consult a healthcare professional. |
Mitigating the Risks and Fasting Safely
If considering the intensive phase of The Fast 800, it is crucial to take steps to minimize potential harm. Firstly, and most importantly, consulting a doctor is non-negotiable, especially for those with existing health conditions. The NHS also states that very low-calorie diets should be undertaken under medical supervision. You can read more about NHS advice on obesity treatment here: NHS guidance on very low calorie diets.
Key strategies for safe implementation include:
- Prioritize Nutrient-Dense Foods: Focus on consuming high-quality, whole foods rich in protein, fiber, and healthy fats, such as those prescribed by the diet's Mediterranean model. This helps maximize nutritional intake within the calorie limit and promotes satiety.
- Ensure Adequate Hydration: Drinking plenty of water is essential to combat headaches and fatigue associated with the initial adjustment phase.
- Consider Supplements: Discuss with your doctor whether a multivitamin and mineral supplement is necessary to prevent nutrient deficiencies during the intensive period.
- Incorporate Resistance Training: To help preserve muscle mass during weight loss, including resistance training is highly recommended.
- Plan the Transition: Do not use the rapid phase as a standalone solution. Have a clear plan to transition to the less restrictive 5:2 or Way of Life phases to avoid rebound weight gain.
Conclusion: The Final Verdict on The Fast 800
So, is Fast 800 bad for you? The answer is nuanced. For a select group of individuals who are overweight or obese and are under strict medical supervision, the intensive phase of the Fast 800 can be a highly effective tool for rapid weight loss and improving metabolic health, with research supporting positive outcomes for type 2 diabetes remission. The diet's long-term phases are also based on the well-regarded Mediterranean diet, promoting sustainable health habits.
However, for many, the extreme calorie restriction is potentially dangerous and unsustainable, posing risks of nutrient deficiency, metabolic slowdown, and various unpleasant side effects. The risk of developing or worsening eating disorders is a serious concern that should not be overlooked. Ultimately, The Fast 800 is not a magic bullet for all and requires careful consideration of personal health, lifestyle, and the willingness to seek professional medical guidance. It is a powerful but potentially risky tool that is best suited for specific, short-term therapeutic purposes rather than as a universal weight-loss solution.
