The Science

The Fast 800 is the umbrella term for a healthy lifestyle based on scientific evidence, encompassing diet, movement and mindfulness. 

So much of the noise in the diet and health industry is based on “fad” and “yo-yo” dieting which has created a legacy of poor health and negative experience.

Our commitment is to act with integrity, while being guided by actual science and data, to do the best for our customers and community, so that we can all live healthier lives.

Key results


Average weight lost


Average weight loss in those with obesity at 3 months


Average weight loss in those with obesity at 12 months


53% of type 2 diabetics showed blood sugars that were no longer in the diabetic range


55% of type 2 diabetics with normal BMI reduced their blood sugars to below the diabetic range


61% of obese prediabetics returned to normal blood sugars after 12 weeks


Average decrease in HbA1c (blood sugar) in diabetic members was 28 mmol/mol, which is clinically significant


Waist circumference reduction was 4.7cm for members with obesity

The Fast 800 Online Programme was independently validated

An independent analysis of our two year results of 23,745 members shows significant weight loss and improvements in blood sugar levels.

The Fast 800 Online Programme aligns with the NHS Diabetes Prevention Programme and the National Institute for Health and Care Excellence (NICE). It integrates the key methods used in rapid weight loss clinical trials providing a sustainable approach to weight loss and diabetes remission.

I am really delighted to share these results with you

They are based on data which has been collected from over 23,000 members who have used The Fast 800 programme and which has been analysed by independent experts. The results show some really impressive and sustained weight loss as well as big improvements in blood sugar levels. I knew the programme was based on the latest science but it is hugely gratifying to see it working so well for so many people.

Dr Michael Mosley

The Fast 800 results in real health benefits

Weight loss

3 months 6kg

Members following the Online Programme for at least three months lost 6kg.

Members with obesity 7.3kg

Members with obesity (BMI ≥ 30) at three months lost 7.3kg.

Long-term sustained weight loss

Long term 8.7kg

Members with a BMI ≥ 30 were likely to sustain an average weight loss of 8.7kg at 12 months.

Waist circumference reduction

Average 4.7cm

Members with a BMI ≥ 30 saw a significant reduction in waist circumference. Losing on average 4.7cm after 12 weeks has significant health benefits.

Improved blood sugar levels


Members with prediabetes with a BMI ≥ 30, 61% had blood sugars returned to normal after 12 weeks.


53% of members with type 2 diabetes had blood sugar levels that were no longer in the diabetic range after 12 weeks.


55% of type 2 diabetic members with a normal BMI reduced blood sugars to below the diabetic range of HbA1c 48 mmol/mol (6.5%).

Lower HbA1c levels

Average 28 mmol/mol

The average decrease in HbA1c values within the diabetic member group was 28 mmol/mol, which is clinically significant.

The independent analysis found

  1. During The Fast 800 rapid weight loss phases, where members eat just over 800 calories a day for a short period of time, most experience clinically significant weight loss.
  2. Intermittent fasting approaches, as practised during The Fast 800 Online Programme, result in positive health outcomes compared to continuous energy/calorie restriction.
  3. A low carb Mediterranean diet - the foundation of The Fast 800 Online Programme - resulted in more weight lost and better long-term weight maintenance when compared to low-fat diets.
  4. For type 2 diabetics, The Fast 800’s high intensity interval training (HIIT) exercise resulted in better immediate glycaemic control than moderate-intensity training.
23,745 members in total were audited
56% started with a BMI within the obese range
244 were in diabetes or prediabetes range

A summary of the independent analysis

The research analysed data from 23,745 members with a BMI range between 18.5 - 48.0 (with a healthy BMI considered to be 18.5 - 24.9).

Of these members, 56% were within an obese BMI range of 30.0 - 48.0.

Within the data set, 244 members began the Online Programme with HbA1c values in the diabetes (HbA1c ≥ 48 mmol/mol or > 6.5%) or prediabetes (HbA1c 42 - 47 mmol/ mol or 6-6.4%) range.

Independent healthcare advisors who work in partnership with NHS organisations

Further research to support the principles of The Fast 800

800 Calories and Rapid Weight Loss

The DiRECT Trial

Background: A major study that explored the power of an 800 calorie/day diet for 3-5 months to achieve major weight loss and remission of type 2 diabetes. The study divided participants into two groups: the first group (the intervention group) were placed on an 800 calorie diet and the second group (the control group) were given the usual NHS treatment for type 2 diabetes.

Results: A staggering 46% of participants in the intervention (800 cal) group achieved remission of diabetes, compared to only 4% in the control group. Weight loss statistics were equally impressive; after 12 months, 24% of the 800 group had still lost more than 15kg of weight, compared to 0% in the control group. Not only did they lose more weight, but also kept more of it off.

Find out more: Lean, M., Leslie, W., Barnes, A., et al. (2018). Primary care-led weight management for the remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet, 391(10120), pp. 541-551.

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Background: Obese and overweight participants were assigned to either an 800 calorie/day diet for 8 weeks, or a control group who were given the current usual care support. The 800 cal diet was coupled with behavioural support and a structured food reintroduction.

Results: The intervention (800 cal) group lost over three times more weight than the control group, losing an average of 10.7kg 12 months after starting the programme. 45% of participants in the 800 cal group lost more than 10% of their initial body weight. The intervention group also showed more improvements in various other health markers than the control group.

Find out more: Astbury, N., Aveyard, P., Nickless, A., Hood, K., Corfield, K., Lowe, R., Jebb, S. (2018) Doctor Referral of Overweight People to Low Energy total diet replacement Treatment (DROPLET): pragmatic randomised controlled trial. BMJ, 362:k3760.

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Background: The PREVIEW lifestyle intervention study  is, to date, the largest, multinational study aimed at preventing type 2 diabetes.  2,326 pre-diabetic patients from eight countries followed an 800-calorie diet for eight weeks as part of a longer term weight loss management and diabetes prevention study.

Results: After eight weeks, participants had lost an average of 11kg, and experienced an average reduction of 10cm in waist size.

Find out more: Christensen, P, Meinert Larsen, T, et al. (2018), ‘Men and women respond differently to rapid weight loss: Metabolic outcomes of a multi-centre intervention study after a low‐energy diet in 2500 overweight, individuals with pre-diabetes (PREVIEW)’ Diabetes Obes Metab. 2018; 20: 2840– 2851. doi:

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Background: A key recent study performed by Oxford University and Dr Clare Bailey looking at the feasibility of using an 800 calorie, low-carb, Mediterranean-style diet as a treatment for people with type 2 diabetes.

Results: After 8 weeks in the rapid weight loss group, average weight loss was 9.5kg, sustained over the course of the trial. Results also included a significant drop in blood sugars, blood pressure and the use of medication (none of which improved in the controlled group, who were following a standard diet). There were no significant side effects.

Find out more: Morris, E, Aveyard, P, Dyson, P, et al. (2017). A food‐based, low‐energy, low‐carbohydrate diet for people with type 2 diabetes in primary care: A randomized controlled feasibility trial. Diabetes Obes Metab. 22: 512– 520.

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Intermittent Fasting

Fasting-Mimicking Diet (FMD)

Background: Another major study, this time looking at the effect on various health markers of a very low calorie diet (700-1000 kcal/day) for 5 days every month for 3 months.

Results: The three cycles of FMD reduced body weight, trunk and total body fat, blood pressure and IGF-1 in comparison to a normal diet. These results were especially pronounced in the most ‘at risk’ portions of the trial groups.

Find out more: Wei, M., Brandhorst, S., Shelehchi, M., et al. (2017). Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer and cardiovascular disease. Sci Transl Med, 9(377).

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Intermittent Fasting vs Conventional Dieting

Background: This study compared the effects of 3 months of Intermittent Energy and Carbohydrate Restriction (IECR) compared to conventional Daily Energy Restriction (DER). The IECR group followed a 5:2 plan with 600-650 kcal/day on fasting days.

Results: The participants on the IECR diets had lost, on average, twice as much body fat as those on the DER diet. Participants on the IECR diets also had significantly greater reductions in insulin resistance than those on the DER diet.

Find out more: Harvie, M., Wright, C., Pegington, M., et al. (2013). The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. British Journal of Nutrition, 110(8), pp. 1534-1547.

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Intermittent Fasting and Asthma in Overweight Subjects

Background: This study examined the effects of alternate day calorie restriction (ADCR) on various health markers for overweight patients (BMI >30) with asthma. Participants spent 8 weeks eating normally every other day and eating 20% of their usual calorie consumption on the intervening days.

Results: Participants who stuck to the diet lost 8% of their initial body weight on average during the 8 weeks. Subjects’ asthma-related symptoms, control, peak expiratory flow (PEF) and quality of life (QoL) significantly improved. Results showed that an ADCR diet can have rapid and sustained beneficial effects.

Find out more: Johnson, J. B., W. Summer, R. G. Cutler, B. Martin, D. H. Hyun, V. D. Dixit, M. Pearson, M. Nassar, S. Maudsley, O. Carlson, S. John, D. R. Laub and M. P. Mattson (2007) Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radic Biol Med, 42(5), pp. 665-674.

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Mediterranean Diet


Background: This was a very large trial involving 7447 individuals, who were at high risk of cardiovascular disease. Participants were randomised to a med diet supplemented with either nuts or extra virgin olive oil, or to a low-fat control group. The effects of the diet after more than 5 years observation were then investigated.

Results: A large number of papers have been published on this trial, and so the key results from each will be summarised very briefly here.

  • A Mediterranean diet was shown to reduce the risk of a major cardiac event by 30% in the trial cohort.
  • The Med + nuts diet was associated with a 13.7% reduction in prevalence of metabolic syndrome.
  • Oxidised cholesterol levels, along with several other heart disease risk factors, reduced significantly in the groups on the Mediterranean diet.
  • The Mediterranean diet reduced the risk of developing type 2 diabetes by 52%.
  • The Mediterranean diet had beneficial effects on various cardiovascular risk factors including blood sugar levels and blood pressure.

Find out more:

Estruch, R., Ros, E., Salas-Salvadó, J., et al. (2013) Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. N Eng J Med, 378, e34.

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Salas-Salvadó, J., Fernández-Ballart, J., Ros, E., et al (2008) Effect of a Mediterranean Diet Supplemented With Nuts on Metabolic Syndrome Status: One-Year Results of the PREDIMED Randomized Trial. Arch Intern Med, 168(22), pp. 2449-2458.

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Fitó, M., Guxens, M., Corella, D., et al. (2007) Effect of a traditional Mediterranean diet on lipoprotein oxidation: a randomized controlled trial. Arch Intern Med, 167(11), pp. 1195-1203.

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Sala-Slavadó, J., Bulló, M., Martínez-González, MÁ (2011) Reduction in the incidence of type 2 diabetes with the Mediterranean diet: results of the PREDIMED-Reus nutrition intervention randomized trial. Diabetes Care, 34(1), pp. 14-19.

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Estruch, R., Martínez-González, MÁ., Corella, D., et al (2006) Effects of a Mediterranean-style diet on cardiovascular risk factors: a randomized trial. Ann Intern Med, 145(1), pp. 1-11.

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Adherence to Mediterranean diet and health status: meta-analysis

Background: This meta-analysis, conducted in 2008 by the University of Florence, reviewed the findings of 12 studies, together following 1.5m people.

Results: It found that those following a Mediterranean diet were 9% less likely to die young, and also less likely overall to die of heart disease, stroke or cancer. They were also less likely to develop Parkinson’s disease or Alzheimer’s.

Find out more: Sofi F., Cesari F., et al. (2008), ‘Adherence to Mediterranean diet and health status: meta-analysis’ BMJ 2008; 337:a1344, doi

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