People have been ‘inventing’ new magical weight loss diets for as long as I can remember.
Some honourable mentions include the wine and eggs diet pushed by Vogue in the 1970s, the cabbage soup diet of the 1980s, and we all remember the Atkins. If we go back to the 1800s, there was even a diet based on arsenic – the stuff that is so toxic it can kill you – and another where people voluntarily swallowed a tapeworm because… well because they were a bit thick, I suppose.
While the next fad diet may be nothing new, there is no shortage of new diets coming to market, and one of the latest to hit the headlines is the Fast 800 Diet.
Given the chequered history of diet plans people are understandably asking whether the Fast 800 will actually work, and most importantly if it is safe.
These are the questions I will answer, and you may be pleased to know from the outset that this one has more credibility than most.
The 3 Stages of the Fast 800 Diet
You have probably heard of Dr Michael Mosley.
He studied medicine but then went into the world of television, working for the BBC as a producer, journalist, and presenter. His documentaries were famous for promoting intermittent fasting among other things, and the Fast 800 is one of his creations. This is why it has more credibility than your typical fad diet.
The Fast 800 is split into 3 stages:
- Rapid Weight Loss Phase – Lasting up to 12 weeks, you follow an 800 calorie per day eating plan consisting of fairly low-carb, Mediterranean-style food. Meal replacement shakes that are high in fibre, protein and healthy fats are also available. The bigger you are the closer to the 12 week maximum this stage will last, and the aim is to put your body into ketosis. Going past 12 weeks is not healthy though, so ideally you should end stage one way before that point.
- Intermittent Fasting Stage – Now you only have to stick to 800 calories for two days of the week, eating a regular amount on the other five. This is effectively Mosley’s 5:2 Diet. The food you eat is still low carb and Mediterranean in style, so things like vegetables, wholegrains, nuts and lean proteins. At this point, the focus is on maintaining muscle mass and supporting your metabolism.
- Maintenance Phase – Once you have achieved your goal or target weight, your focus shifts to maintaining it. You can ditch the 800 calorie days now, although it’s ok to still do it once a week if needed, but stick to the same sorts of foods as you have been eating, so fewer starchy carbs and low sugar. At this point, it’s about finding a balance that fits with your lifestyle.
The whole concept is built on the back of Mosley’s previous diets, the 5:2 Diet and the Blood Sugar Diet, along with additional research around low carb low calorie diets and intermittent fasting.
There is a lot of evidence to back it up, but as with anything like this, there are those who warn against it too. The main criticism of the Fast 800 diet is that there is no evidence that says it is any more effective than traditional diet and exercise plans. It can undoubtedly help someone lose weight quickly, but the first phase can be tough to stick to and there may be side effects such as headaches, tiredness and constipation.
Safety Concerns and Diabetes
Like any very low calorie diet (VLCD), it’s not designed for the long term.
Our bodies need more than twice the calories suggested in the Fast 800, so reducing your intake to such a low level is bound to have consequences if you aren’t careful about it. The line between fasting and starving yourself is not always obvious.
NHS guidance does support Mosley’s 12 week maximum for that first stage, but even so, I would be cautious letting it last that long and would certainly recommend listening to your body if you start to develop problems. The NHS also suggests anyone following a VLCD should do so under the guidance of a medical professional.
The shakes are another element to be wary of. While they do supply many of the nutrients and vitamins our body needs, they are not a total substitute for real food. They should not be used as substitutes for more than 2 meals per day or more than 10 meals per week.
In terms of safety then, so long as you follow the guidance you should stay fit and healthy – just be prepared to adapt if your body tells you to.
On the flip side of this, it is thought the plan could help ‘reduce or delay the complications’ of type 2 diabetes. Elements of the diet are based on a successful study by Professor Roy Taylor, which looked into the effects of intensive weight management and monitored participants for several years afterwards. It found an ongoing positive impact in participants with type 2 diabetes 2 years after the study ended.
That said, the diet is not suitable for people on insulin or with type 1 diabetes, anyone who is underweight or has an eating disorder, anyone recovering from surgery, or anyone with a heart condition, so do bear that in mind.
People Who Tried It
Since the Fast 800 Diet became so popular a lot of people have been sharing their progress on social media, so I thought it would be a nice touch to have a look at some of them and see how it has gone.
First off is Jo, who loves the diet so much her handle is fast800_jo!
View this post on Instagram
As you can see, the diet was part of a health and fitness regime that helped Jo shed 4 stone over time, before she relaxed a little bit and let her weight settle at just under 12 stone.
This is a good example of how the Fast 800 can give you that initial weight loss confidence you need to make lifestyle changes that become permanent.
No photos on the next one, but Victor demonstrates a fantastic approach to the diet:
Just 2 days into the Mosley Very Fast 800 Diet… 800 cals a day. Already lost 4lbs (over 2 kg). Objective is to lose 14lbs in 3 weeks but hoping in 2. You can go over to the 5:2 diet after a fortnight. But 800 cals with small variation is ok so far, lots of water and coffee. No…
— Victor Olliver (@VictorOlliver) July 22, 2023
He has a solid plan in his head with a set goal he wants to achieve, and after two days has already lost over 2kg. This just proves the point that the initial rapid weight loss stage really does bear fruit.
Lastly, we will look at the hilariously named, SavingCaloriesforCocktails.
Her real name is Paloma, and she offers a good idea of the medium term results that can be achieved with the Fast 800 diet:
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At 60 years old, Paloma went from 156.5 pounds (11.1 stone) on the 1st of January to 142.5 pounds (10.1 stone) in May. So she lost a stone in 5 months, but just look at the difference in her physique.
It’s not always the weight that matters, but where you lose it from. Plus, if you are exercising and gaining muscle at the same time, you will be swapping out fat for muscle, so the weight becomes a bit of a red herring.
All of these people have had success with Fast 800, whether that be early success, mid-term success, or long term sustained success, so if it is something you are considering it can 100% work for you if you do it safely and correctly.