Exploring the Science: What is the Mosley diet?

October 3, 2025 •

3 min read

In 2012, Dr. Michael Mosley, a physician and journalist, famously reversed his own type 2 diabetes by using intermittent fasting and a low-carb diet, prompting widespread curiosity about his methods. The comprehensive eating plan he developed answers the question: What is the Mosley diet? It is a flexible, science-based approach designed for significant weight loss and improved metabolic health.

Quick Summary

The Mosley diet is a series of eating plans centered on intermittent fasting and a low-carb Mediterranean style. It includes the intensive Fast 800 and the more sustainable 5:2 diet, aimed at weight loss and better health.

Key Points

Origin: Developed by Dr. Michael Mosley, the diet was inspired by his personal success reversing type 2 diabetes using intermittent fasting.
Core Principles: The diet combines intermittent fasting with a moderately low-carb, Mediterranean-style eating pattern rich in whole foods.
Three Main Approaches: It offers phases for rapid weight loss (Very Fast 800), gradual weight loss/maintenance (New 5:2), and a long-term healthy lifestyle (Way of Life).
Health Benefits: Potential benefits include weight loss, improved insulin sensitivity, reduced blood pressure, and better metabolic health.
Important Considerations: The intensive phases may not be suitable for everyone and require medical consultation, especially for those with existing health conditions or a history of eating disorders.

The Origin and Philosophy of the Mosley Diet

Dr. Michael Mosley's personal health journey, which included high blood sugar, cholesterol issues, and a type 2 diabetes diagnosis, led him to explore intermittent fasting. His 2012 BBC documentary, Eat, Fast and Live Longer, showcased a two-day-a-week calorie restriction approach, which he used successfully to reverse his diabetes. This work became the foundation for the Mosley diet, a series of popular books and programs.

Rather than a single rigid plan, the Mosley diet is a phased program combining a moderately low-carb, Mediterranean-style diet with intermittent fasting to create a calorie deficit for weight loss. It emphasizes nutrient-dense whole foods to manage hunger and improve health.

The Core Principles of the Mosley Diet

Intermittent Fasting: Cycles between periods of eating and fasting, aiming to shift the body's energy source from sugar to fat.
Mediterranean-Style Eating: Focuses on vegetables, quality proteins, healthy fats (like olive oil), and fiber, while limiting processed foods, sugar, and refined carbs.
Low-Calorie Windows: Specific days or periods involve reduced calorie intake to achieve weight loss.

The Different Approaches to the Mosley Diet

Dr. Mosley's program offers different phases catering to various needs and goals.

The Very Fast 800

An intensive phase for rapid weight loss and improving metabolic health.
Involves consuming 800 calories daily for up to 12 weeks.
Suitable for those needing significant weight loss or with blood sugar issues.

The New 5:2

A more sustainable plan for weight loss or maintenance.
Requires 800 calories on two non-consecutive days each week.
Other days follow a moderately low-carb Mediterranean diet without strict calorie counting.

The Way of Life

The final stage for long-term health maintenance.
Focuses on a Mediterranean-style, low-carb diet without calorie counting or fasting days.

Comparison of Mosley Diet Approaches


Feature	The Very Fast 800	The New 5:2	The Way of Life
Goal	Rapid weight loss, metabolic health reset	Gradual weight loss, long-term maintenance	Sustainable health and weight maintenance
Calorie Intake	800 calories daily	800 calories on 2 days, unrestricted on 5	No calorie restriction
Duration	Up to 12 weeks	Long-term	Indefinite
Fasting Frequency	Continuous low-calorie intake	2 non-consecutive days per week	No dedicated fasting days
Diet Style	Low-carb Mediterranean	Moderately low-carb Mediterranean	Moderately low-carb Mediterranean
Target User	Significant weight loss, type 2 diabetes	Moderate weight loss, maintenance	Ongoing healthy lifestyle

Foods to Eat and Avoid

The diet emphasizes whole, unprocessed foods and limits refined items.

Foods to Enjoy

Non-starchy vegetables.
High-quality proteins (fish, poultry, eggs, legumes).
Healthy fats (olive oil, nuts, seeds, avocados).
Moderate amounts of full-fat dairy, berries, apples, and pears.

Foods to Limit or Avoid

Refined carbohydrates (white bread, pasta, rice).
Added sugars and sugary drinks.
Processed meals and snacks.
Frequent snacking.

Benefits and Considerations

Research supports the benefits of intermittent fasting and Mediterranean diets for metabolic health, including improved insulin sensitivity and reduced blood pressure. The initial phase can lead to significant weight loss, including visceral fat reduction. However, the restrictive 800-calorie phase can be challenging and has raised concerns about extreme dieting. Initial side effects like hunger and fatigue are possible.

For more detailed scientific findings on intermittent fasting and blood sugar regulation, you can explore research funded by organizations like Diabetes UK, which inspired elements of the Mosley diet.

Who Should Not Follow the Diet?

Consulting a healthcare professional is crucial before starting this diet, as it's not suitable for everyone. It is generally not recommended for:

Pregnant or breastfeeding women.
Individuals with a history of eating disorders.
Those with existing medical conditions, particularly type 1 diabetes.
Individuals who are underweight.

Conclusion

The Mosley diet offers a science-based approach to weight loss and metabolic health through its phases (Fast 800, New 5:2, and Way of Life), combining intermittent fasting with a low-carb Mediterranean diet. While it provides a structured path for potential benefits, its intensive nature requires careful consideration and medical consultation, especially before beginning the more restrictive phases.

Frequently Asked Questions

The Mosley diet was created and popularized by British physician and journalist Dr. Michael Mosley, who first explored intermittent fasting in a 2012 BBC documentary.

The Fast 800 is one of the intensive phases of the broader Mosley diet plan. The Mosley diet also includes the more sustainable 5:2 approach and a non-fasting maintenance plan called 'The Way of Life'.

The Mosley diet encourages a healthy, low-carb Mediterranean-style diet on non-fasting days. While there's no strict calorie counting in later stages, it's not a license to eat junk food, which would hinder weight loss.

Some common side effects, especially during the initial intensive phase, include headaches, fatigue, and irritability. These can often be managed with proper hydration and are a normal adjustment period.

The Very Fast 800 plan, which involves eating 800 calories daily, is recommended for a maximum of 12 weeks or until a healthy BMI is reached. It should then be transitioned to a less restrictive phase.

Dr. Mosley initially used this diet to reverse his own type 2 diabetes, and studies have shown its effectiveness in improving blood sugar control. However, people on diabetes medication must consult a doctor and be monitored, as it can cause dangerous blood sugar lows.

Yes, exercise is encouraged, even on fasting days. Light to moderate activity like walking or yoga is suggested during the most restrictive phases, with more strenuous exercise incorporated later.