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Dr Michael Mosley’s Advice For The Over-Weight To Lose Weight – Safely And Quickly

overweight man

There has been some recent speculation in the media surrounding the safety of rapid weight loss and some have questioned how realistic it is to achieve and sustain.  From my own personal experience with rapid weight loss, I can tell you it is all three. 

There is a widespread belief that if you lose weight fast, then you will put it on even faster, but that is not true.  The reason I recommend a rapid weight loss diet for those who are suitable, is because of a number of large studies showing that when they are done properly, they are safe and far more effective than the standard “slow and steady” weight loss advice.

These studies also show what can happen if you ignore the problems of obesity and just continue to follow usual advice.

In a recent review article titled ‘Myths, Presumptions and Facts about Obesity’ in the prestigious medical journal, The New England Journal of Medicine, researchers put this claim firmly into the “myths” category. 

“After looking at numerous studies which have compared rapid with slow and steady weight loss, they concluded that you would do better to lose it quickly rather than slowly. A recent Australian study backs up these claims.

Researchers took 200 obese volunteers and put half of them on a low calorie diet (less than 800 calories a day) for 12 weeks. The other half were asked to cut their calories by 500 a day (enough to lose around a pound a week).

“They were then asked to do this for 36 weeks. There was a very high drop-out rate among the steady dieters: less than half made it to the end of the 36 weeks.

Most said they gave up because they were frustrated by the slow rate of progress. By comparison, more than 80 per cent of those in the rapid weight loss programme stuck to it.

They were then followed for three years. Although both groups put some weight back on, the amounts were similar. Katrina Purcell, a dietitian who led the study, said at the time, ‘Our results show that achieving a weight loss target is more likely, and drop-out is lower, if losing weight is done quickly.’

Most rapid weight loss studies are now based on 800 calories a day which is high enough to be sustainable and give the nutrients you need, and low enough to lead to rapid weight loss and other beneficial health changes. 

This is one of the main reasons why Clare and I came up with the idea of The Fast 800, which is an online programme that uses the fundamental principles of intermittent fasting, time restricted eating, both underpinned with the Mediterranean diet for weight loss.

One of the great things about The Fast 800 is its flexibility – you can tailor this diet to suit your needs, goals and motivation. There are three key stages to this diet: The Very Fast 800, The New 5:2 and The Way of Life.  Each stage is designed to fit your desired agenda. 

All of the stages are fluid and you might find that you drift naturally between stages, depending on your personal circumstances and goals. Take a look at for recipes, articles and tips on sustaining this healthy lifestyle.

You might worry about getting hungry but most people who fast say that within a very short time their hunger passes. Rapid weight loss encourages your body to switch over to fat burning. It also reduces insulin levels, increases growth hormone and boosts levels of a hormone called BDNF in the brain, which helps improve your mood. 

Last year Dr Bailey used our 800 calorie, low-carb, Mediterranean-style diet in a randomised controlled trial, run with Oxford University, for overweight and obese patients with type 2 diabetics.

The results of the study, called Diamond, were recently published and showed average weight loss after 8 weeks of 9.5kg in the rapid weight loss group, sustained over the course of the trial, and 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.

Participants and healthcare professionals reported growing engagement, confidence and motivation after seeing the initial rapid results. Participants reported positive impacts on their emotional and psychological well‐being and influence within their social circle.

Healthcare professionals considered the follow‐up contact was popular and motivating for participants and also improved their own motivation and engagement with the intervention, and their belief that it could improve patient outcomes. 

Participants derived continuing motivation from observing measurable changes, whether objective (eg, a reduction in glucose or blood pressure) or subjective (eg, perceived changes in activity or appearance). Healthcare professionals and participants perceived that the potential to reduce or stop medications was a strong motivator for initial engagement and sustained adherence.

I think the clearest evidence for Intermittent Fasting comes from people who are overweight or obese. That said, there are people who are not overweight, but nonetheless have pre-diabetes or raised blood sugar levels.

This is particularly common in the Asian community and with some other ethnic groups, and indeed around a quarter of people that have type two diabetes are not actually classified as overweight, although they will typically have a slightly larger tummy.

So, in those groups, intermittent fasting can be very helpful for bringing your sugars down. Generally speaking, we don’t recommend it for people who are a normal BMI, because the evidence is much clearer in people who are overweight or obese. It’s not dangerous, particularly if you’re doing the sort of 5:2 technique, but we certainly wouldn’t recommend it for anybody whose BMI is below 20 or 21.

Rapid weight loss is not suitable for everyone and on The Fast 800, we recommend you only do it if you are significantly overweight, or obese, and only for up to 12 weeks.

However, The Fast 800 online programme is not just for those with an unhealthy BMI. Our other, more flexible approaches, are suitable for those looking to improve their overall health.  If you are considering The Fast 800, we recommend consulting your usual healthcare professional before making any significant changes to your diet or exercise regime.

Founded and developed by a group of qualified doctors and health professionals, the whole philosophy of The Fast 800 online programme is based upon scientific evidence.

A 12-week programme – do-able in your own home – on costs £99 and includes:

  • Gut-friendly, foods to support your immune system, calorie-counted and based on Med-style food
  • An online personal assessment to determine the right level of fasting for you
  • A flexible meal planner and automated shopping lists to keep your plan simple
  • More than 300 easy-to-make and “taste great” recipes
  • Loads and loads of support on how to adapt your routine, especially at a time of COVID-19
  • Guided exercise programmes you can do at home, and without equipment
  • Online support from our team of Health Coaches, on hand for advice, support and motivation
  • A lively and inspirational cohort of members united by the goal to improve their health
  • Weekly educational articles and videos, so that you are empowered to make these changes for life!