Dr Michael Mosley’s Fast 800 Diet: What the Weight-Loss Plan Involves

Dr Michael Mosley’s Fast 800 approach became widely known for combining intermittent fasting, Mediterranean-style eating and increased physical activity as part of a structured weight-loss programme.

Mosley, who became a prominent health and wellbeing broadcaster and author, promoted several approaches to weight management, including the 5:2 diet and the Fast 800. His work has continued to influence discussions around nutrition and healthy weight loss following his death in 2024.

One version of the Fast 800 programme involves a short period of significantly reduced calorie intake, with some plans recommending around 800 calories a day for a limited period. The approach was designed as an intensive phase for people seeking substantial weight loss, rather than as a permanent eating pattern.

How the Fast 800 approach works

The diet combines calorie restriction with principles associated with the Mediterranean diet. Meals typically focus on foods that are rich in protein, fibre and healthy fats while limiting refined carbohydrates and processed foods.

Suggested protein sources include oily fish, seafood, chicken, turkey, lean meats, eggs, beans, dairy products, nuts and seeds. Vegetables and other nutrient-rich Mediterranean-style foods also form an important part of the eating pattern.

Depending on the version of the programme, people may divide their daily intake between two or three meals and avoid frequent snacking. Some plans have also included meal-replacement products as an option.

Mosley also promoted intermittent fasting as part of longer-term weight management. After the intensive phase, the programme could transition towards a modified 5:2 approach, involving lower-calorie days during the week combined with overnight fasting.

Exercise and meal planning

Physical activity was another component of the approach. Mosley recommended incorporating resistance exercises and short periods of high-intensity interval training, alongside regular movement.

Meal preparation was also encouraged as a way of making the programme easier to follow. Planning meals in advance can help people maintain consistent eating habits and reduce the temptation to snack, particularly when preparing food for other family members.

Can it help with weight loss before Christmas?

A 10-week programme beginning in early September could potentially produce significant weight loss for some people before the festive period. However, there is no guarantee that following the Fast 800 approach will result in losing two stone, as weight-loss results depend on factors including starting weight, age, health, activity levels and adherence to the programme.

The amount of weight considered healthy to lose also differs from person to person. Rapid weight-loss programmes should therefore be approached carefully.

Important health considerations

An intake of around 800 calories per day is considered a very-low-calorie diet and is not appropriate for everyone. Such restrictive diets should generally only be followed with suitable medical or professional supervision, particularly by people with existing health conditions or those taking medication.

The Fast 800 was intended as a short-term intervention rather than a permanent lifestyle. Anyone considering a very-low-calorie diet should speak with a doctor or qualified healthcare professional first to determine whether it is safe and appropriate for them.

For people who want to lose weight, sustainable changes such as eating a balanced diet, increasing physical activity and developing healthy long-term habits may be more appropriate than pursuing rapid weight loss.

Note: This article is for general information and should not be treated as medical advice. Individual dietary needs vary, and readers should seek professional advice before starting a restrictive weight-loss programme.