Last updated on February 2nd, 2019
Fast 800 Diet – By Michael Mosley
The Fast 800 Diet is a very low-calorie diet (VLCD) developed by Dr. Michael Mosley.
Make no mistake about it, this is a hardcore diet that involves severely restricting the amount of calories you eat each day. However, Mosley claims his Fast 800 Diet can provide rapid weight loss and may also reduce the risk of type 2 diabetes.
There can be little doubt about the claims of weight loss. Anybody who sticks religiously to any form of VLCD is guaranteed to lose weight fast. The body becomes so short of calories it would be impossible not to.
The average man requires 2,500 calories per day. This will be enough to support his daily energy requirement. Nothing more, nothing less. Consuming more than this will result in weight gain. A lesser amount of calories per day will necessitate the need for fat burning.
Women don’t generally require as many calories as men do each day. The average woman only needs to eat 2,000 calories per day to maintain her weight.
This isn’t rocket science. Anyone who has a simple grasp of mathematics should be able to see following the Fast 800 Diet will cause the body to experience an immense shortage of calories.
Who Is Dr. Michael Mosley?
Although the BBC and most other websites state Mosley trained as a medical doctor or simply say he trained in medicine, this is not very informative. It’s also misleading.
Finding reliable sources of information about his qualifications is hard work. Even his profile at LinkedIn contains only the sparsest amount of information about his credentials.
It states he studied PPE at Oxford. That’s not related to medicine. PPE is Philosophy, Politics, and Economics. His profile does not mention any medical credentials at all. [SOURCE]
However, in an interview with the BMJ, Mosley states he originally trained as a psychiatrist. He became disillusioned during a psychiatry placement and took a job with the BBC instead. [SOURCE]
Mosley has enjoyed a long and distinguished career in broadcasting and now works at the executive level in the BBC. However, apart from his involvement in shows like Trust Me I’m a Doctor, he is probably best known as the man behind the 5:2 Diet.
What Is the Fast 800 Diet?
According to Mosley, his Fast 800 diet takes all the latest cutting-edge theories on intermittent fasting and weight loss and combines them in a flexible and easy-to-follow plan.
He also describes it as a “dramatic update” on his 5:2 Diet that will take intermittent fasting to the next level.
Intermittent fasting is an umbrella term that encompasses all the various diet plans that involve set cycles of eating and fasting.
Also known as the Fast Diet, the 5:2 Diet allows people to eat normally for five days each week. The days of eating normally are followed by two days of fasting on which the calorie intake has to be restricted to 500—600 calories per day.
Based on his interpretation of specific studies, Mosley now believes 800 calories per day is the “magic number for weight loss”.
He says 800 calorie a day allows you to eat enough fat, protein, and important nutrients to feel satisfied while still allowing you to get all the benefits of fasting.
Mosley also thinks his latest diet makes fasting easier to do.
Time Restricted Eating: A New Approach to Fasting
The Fast 800 Diet involves a new approach to fasting called Time Restricted Eating (TRE). The good news is, Mosley is right. Many people will likely find it easier to do than other forms of fasting.
Although we don’t tend to think of it in these terms, we all fast every day of our lives. During that necessary downtime we call sleep, we don’t eat anything for a number of hours.
This “overnight fast” can be extended by having the last meal of the day earlier than normal. Likewise, it can be prolonged by eating a late breakfast.
By prolonging the overnight fast, people doing the Fast 800 Diet condense their eating into a smaller window of time.
TRE is becoming more popular these days, especially with celebrities, bodybuilders and millennial.
The overnight fast is typically extended to 10—16 hours.
Obviously, the 16 hour fast is the most extreme. It’s likely to be easiest to achieve by combining an early supper with a late breakfast.
X-Men actor, Hugh Jackman, admits to using this form of TRE and says it helped him build his muscular Wolverine physique.
TRE: What the Research Shows
The good news is, some research shows TRE can also prevent metabolic disease.
For the purposes of one study, mice were put on a high-calorie diet, they developed high cholesterol and increased blood sugar. There were also signs of liver damage.
A second group of mice were fed an identical diet within an eight-hour window. Their enforced TRE appeared to protect them from most of the consequences of unhealthy eating.
A later study, carried out on humans in 2017, showed equally promising results. This was the first TRE study involving human volunteers, but it was not the last.
In a smaller study, conducted at the University of Chicago, the TRE group benefited from a drop in insulin resistance (which marks a risk of type 2 diabetes) and better quality of sleep.
Additionally, the members of the TRE group also had more energy and less hunger at bedtime.
How to Do the Fast 800 Diet
For optimum benefits, Mosley suggests beginning with the Fast 800 Diet and using it as way to fast-track your weight loss.
He believes a 16-hour overnight fast works best, but suggest working up to it by using a shorter fast period first.
Then, after a few days, weeks, or months of this, switching to his new 5:2 Diet and using it as a weight maintenance device.
Mosley’s new 5:2 diet differs from his original version because fasters are allowed 800 calories per day instead of 500—600.
Alternatively, it’s also permissible to skip the TRE fast-track period and just jump into the new 5:2 Diet.
It’s also worth noting, dieters have the option of obtaining all their calories from food, or using a carefully selected combination of meals and meal replacement shakes.
The New 5:2 Diet / Fast 800 Diet In a Nutshell
- Choose whether you want to fast-track your weight loss with the Fast 800 Diet or jump straight into the new 5:2.
- Boost the health benefits by eating within a restricted period of time. Start with 12-hour overnight fasts and increase to 16-hour fasts when you are ready.
- Eat no more than two to three meals per day and don’t exceed the 800-calorie limit. Use meal replacement shakes according to your preference.
- On your five non-fast days, eat healthy, low-carb meals inspired by the Mediterranean Diet. There is no need for calorie-counting, but keep the portion sizes small.
The Fast 800 Diet: Why It’s a Controversial Way to Lose Weight
VLCDs are nothing new and are not generally not considered suitable for most people.
Furthermore, they are diets that are so strict they can present health risks and are best done under clinical supervision.
In fact, unless there is a health issue involved that presents health risks, experts say it’s not safe to lose too much weight too fast. The British NHS and American CDC are in agreement on the subject. Both suggest a safe weight loss of one to two pounds per week. [SOURCE 1, SOURCE 2]
VLCDs are normally only deemed suitable for people who have an urgent need to lose weight.
Typical candidates include:
- People who need to lose weight before undergoing surgery
- People preparing for fertility treatment
- Diabetics and people with other health conditions that may find a VLCD beneficial (in a doctor’s opinion)
- People with a BMI of 30+
Speaking in an interview with CNN, Dr. John Hernried from the OTC Medical Weight Loss Group (private clinic) in California said, “Next to bariatric surgery, nothing is more effective for weight loss than a VLCD, including pills and other diets.”
However, he also pointed out such diets are unsuitable for people who only need to lose 10 pounds. Additionally, Hernried pointed out the fact that most programs screen potential candidates to see if they are physically and psychologically fit enough for a VLCD.
Henried, who has over a decade experience supervising VLCDs, also stressed the need for correct supervision: “I would never recommend doing a very low-calorie diet alone.” Patients at his clinic are given regular electrocardiograms and blood tests. [SOURCE]
Fast 800 Diet Benefits
If you do this diet you will lose weight. Don’t doubt it. Your body will be so short of calories it will have to burn fat.
The Fast 800 Diet will also be easier than a lot of other diets that involve fasting. It’s bound to be. Much of your fasting will be conducted while you are asleep. However, easier is not the same as easy. Fasting is always difficult, though it does get easier with time.
According to Mosley, Fast 800 dieters will benefit from various improvements in their physical and mental health.
The alleged benefits include:
- Weight loss
- Improves the mood
- Reduces blood pressure
- Prevents high blood sugar
- Reduces inflammation
- Improves insulin resistance
- Offers protection against type 2 diabetes
Who is the Fast 800 Diet For?
The Fast 800 Diet is for people who are in good health and wish to lose weight. It’s also for anyone who wishes to improve their health and experience an overall feeling of wellbeing.
However, Mosley makes it clear his system is unsuitable for people who are under 18-years of age or for women who are pregnant, breastfeeding, or undergoing fertility treatment.
Nor is it a good option for people who are underweight or have eating disorders, psychiatric issues, or medical problems.
A Look at the Potential Dangers and Side-Effects
VLCDs can cause a number of side effects. Nausea, fatigue, constipation, and diarrhea are a few of the most commonly reported problems. Fortunately, reactions such as these generally disappear within two to three weeks.
However, not all the potential side effects are so mundane. VLCDs can also cause gallstones.
Due to the food restrictions imposed, some people may also find it difficult to obtain a healthy balance of nutrients and fiber. This, in turn, could present further health problems.
So, although the Fast 800 Diet has its merits, there may also be risks involved. [SOURCE]
The Fast 800 Diet is a revised and improved version of the 5:2 Diet.
Mosley has reduced the calorie restrictions imposed by his original diet to allow people to eat 200—300 more calories per day.
He’s also introduced optional extended overnight fasts that are optional but can be used as a weight loss kick-starter.
Both these actions appear to genuine improvements on his original diet. They will make it easier on newcomers to this type of diet while also still supporting weight loss.
Fast 800 Diet is more than capable of helping people to lose weight. It may offer other benefits as well, but it presents the risk of health problems such as gallstones and nausea.
More importantly, the rapid weight loss it provides may not be safe. The CDC and NHS agree a weight loss of one to two pound per week is acceptable. Anything more is not.
This is an eating plan devised by one man and promoted through his Fast 800 Diet book. It’s also had the benefit of significant media attention.
Regardless of whatever qualifications Mosley may or may not have, the Fast 800 Diet is still a controversial diet.
Bearing in mind the potential risks involved, but not forgetting the potential for good, the Fast 800 Diet offers a debatable bag of tricks. If you are thinking of doing the Fast 800 or any other VLCD would be wise to speak to your doctor first.
Should you be lucky enough to get the green light, go full-steam ahead. If not, take your doctor’s advice and give it a miss. Any decision your doctor makes will be based on your medical history and the advice you get will be tailor-made for you.