I am looking at signing up to the online programme and starting on the Fast 800 for 12 weeks.
Two years ago I followed The Blood Sugar Diet and had successful results but, not being (pre-)diabetic, I did not follow a strict 800 calorie day and mostly focused on reducing my carbs and the change in eating habits.

I am a solid, 6 foot, 165kg, male and everyone I speak to feels that 800 calories is insufficient given my size. The most common reaction is “How does this magic number of 800 work – isn’t everybody different?”

Is 800 sufficient regardless of current body mass?
Is there supporting evidence I can point the naysayers to?

Hi Turtle, these questions get asked a lot. The 800 calories comes from a trial by Prof Roy Taylor into treating people who have had bariatric surgery who are seriously obese. Most of these people could only tolerate 600 cals of liquid feed (very carefully made up of all the nutrients needed) and it was by accident that he discovered that most of these people had diabetes then suddenly didnt have it any more. The 600 calorie diet was very carefully supervised in a hospital setting. They lost weight and lost their diabetes. Along comes Dr Mosley who wants to try something similar for himself, having just been diagnosed with diabetes. Being in the circle of medics he contacted Prof. T and came up with the 800 calories real food diet we know as the BSD. The 800 calories is the optimum number that will shock the body into getting rid of the dangerous fat around the organs. Visceral fat. This was particularly important for diabetics as it is believed that visceral fat around the pancreas (where insulin is produced) and the liver (where glycogen is stored and controlled) could shock the body into getting the pancreas to start proper insulin production. Anyway, there is quite a bit more science to it to do with insulin resistance etc. So that is the basis of 800 cals and yes, it is for everyone.
I would say to anyone not diabetic, why would you do this but there are reasons. For one the very fast weight loss in the first few weeks is great, then this gives us motivation to lose more weight. The diet is not meant to be a long term thing and they suggest no more than 12 weeks. However, there are people like me who have been following the principles of low carb, high fat and low calories for several years but this is not a continuous thing. I always stick to the principles of very low carb and almost never eat white starchy carbs so your earlier attempts were perfectly sound, eat less carbs and watch the calories. You might not get that initial high weight loss but then not everyone who is on 800 cals does either. It depends a lot on body composition, how much weight you have to lose and so on.
You probably cannot convince other people that it is a good thing. I have been told over the last 4 years that – I would lose all muscle mass – havent – that my brain would shrivel up because the brain can only work with carbs – tell them to check the carbs in an apple!!! Told I would suffer from malnutrition but I eat a much better diet than I ever did before because I plan and make an effort to have really good nutritious foods like the Med diet style. You just have to keep quiet about how many calories you eat and just say you are on a balanced, nutritious diet.
You mentioned the 12 week paid diet. No one here has paid for that because, if you have one of the 2 books – the BSD or the Fast800 – you have all you need to know along with the support here. There was someone on here a couple of weeks ago who signed up and paid and after 2 weeks asked for a refund. I will try and find their post as to why but it was something to do with someone telling you what to eat in a rigid sort of way and the forum connected to it not being quite so friendly as us lot.
Just one final note – I told my daughter to record the Dr M prog lose a stone in 21 days and she decided to do it with her partner. He lost all his excess weight (around 6kg) in 2 weeks and started to do a maintenance plan and my daughter has lost 5kg and is going to continue as she has more to lose. Her partner is a rugby players and football coach and has been doing the coaching as lock down eased. He managed on the 800 but had a lot of early nights 🙂
Hope that helps – you have done it before and how many cals you eat is your choice but give the 800 a go for a couple of weeks at least. Your body soon gets used to it. Also, there is always someone here who can help you. We all have our own experiences and dont mind sharing. For free.

Hi Turtle,

The point is that you are not limiting your body to 800 calories, you are changing the macros of what you eat to ensure that your body can burn the surplus calories you have previously eaten – ie your fat.

If you eat a high carb diet, it raises insulin levels, when insulin is high your body can’t access your fat stores. keep insulin low and your body can access as many of the calories that you have previously eaten as it wants.

Each lb of fat you carry is 3500 calories. If you keep insulin low your body can access as many surplus calories that you have previously eaten so you are not limiting the number of calories.

The 800 calories is just a limit set to make it easier mentally to feel that you have eaten so you do not feel deprived. Originally apparently it was 500 calories, but it was increased to 800 calories because people were even more concerned about complying with that limit.

Thank you both so much for your replies. I have the BSD and Fast800 books and had started to lean towards not paying for the programme so your comments on that was especially interesting to read @sunshine-girl.
I managed 1200 calories two years ago but never explored ketosis as I was focused on my macros (as you’ve pointed out @jgwen). However, based on the Fast800 and recent UK series, ketosis is a key element to kickstarting things so I really want to give it a go this time around. Folks around me (mostly family) scoff at the idea that 800 calories is adequate. In truth, I found 1200 to be hard to reach some days once I reduced my carbs so I don’t have much concern.. just wanted to confirm my own thoughts which you have both done, so thanks again.

-OMG I hope Dr Mosley doesnt sack me for dissing his other site 🙂

Should mention that one of my naysayers is my doctor. I never told him how many calories but he said it was impossible to live without the starchy carbs, what would I eat. Honestly, doctors have very little training in nutrition – that is a fact not a criticism. The big thing for him was the fact I admitted to eating real fats like full fat cheese and butter instead of marge, full fat yoghurt and so on. I also have oils like rapeseed and olive along with nuts, avocados and other good fats. I don’t eat that much fat as the calorie allowance wouldn’t allow it but it is the fats that keep you fuller. Because of this he insists on testing my cholesterol every 3 months instead of annually. Every time the results come in he still cant believe I have gone from 40 mg statin and cholesterol of 6.7 to 10 mg statin and cholesterol of 4.1. I stopped the statin completely at on point but decided to take the minimum dose as I am at high risk of stroke and heart disease with having diabetes and family history. Also, my BP was 115/80 when he checked it on Tuesday (my last appt), it used to be around 145/80. So this diet does so much more than make you lose weight and reduce blood glucose. There are reports on here of people having long term minor problems just disappear – things like IBS, sleep problems, skin problems. I swear by this diet.

Reading the above but not answering the OPs question I think highlights

1) The national post code NHS lottery
2) How over many years we have been brainwashed into believing what is a healthy diet isn’t.

I was recommended the BSD by my GP to sort out Hypertension (which it did within a week!).

The number of people who cringed when I told them I was eating healthy full fat food, sticking to 800 cals a day. So many people thought it was too extreme and the rapid weight loss wouldn’t stick. And I think we’ve become brainwashed to believe ‘well built’ is healthy, skinny isn’t.

Leo Fung’s Obesity Code is a great read to understand where a lot of these myths came from.

BTW I was 110kg when I started, 6 weeks of 800 cals a day got me to my 10% weight loss. I’ve been maintaining successfully ever since – weight has crept down a little more just sticking to the principles but now level at 90kg!

Freester, if the NHS was referring to my doctord comment, I live in France and doctors here also seem to tow the party line. My doctor said to me (to be said with a French accent) ‘I cannot ask a French person to give up their baguette’. I must point out that was 4 years ago and we no longer discuss what I eat, he just accepts that I will do what I think is best for me. I am not a very good patient in the compliance sense but I am a healthy patient and he appreciates that.

To be honest at 165kg and 6 ft you could probably survive on water for 8 weeks, never mind 800 cals. I think it’s a number that does the job whilst being deemed safe. Expect to not have too much energy initially, expect your mind to play tricks and convince you not to do it, eating is really addictive I found cigarettes easier to give up than calories/carbs. I think there is the possibility you’re a bit daunted, speaking to people almost hoping to hear it’s not right for you, I get told my people that it can’t be healthy and your meant to lose it slowly etc, all uninformed stuff based on out of date thinking. In 8 weeks of work you can change your life (I’ve been there, was in denial about my size and what I needed to do a long time before I went through with it). I was over 125kgs and did the 800 fine (I’m 6f 3 and was a beer drinking rugby player, heard all the same stuff), I even trained through the first session, you have marathons worth of stored energy in your body, you’ll use lots of it during the 800 phase. Check with your doctor if you’re really not sure. I’m now 94kgs and much healthier/happier btw.

My advice is just don’t tell people you are only eating 800 cal – a) it’s frankly none of their damn business, b) it’s backed up by science and c) your plate will still be full – it’s not like you will only be eating minuscule portions for a rabbit, it’s just your plate will be full of low carb, low cal veg rather than big piles of pasta and sauce and bread! Likely if you didn’t point out “hey I’m only eating 800 cal today” most people wouldn’t even notice, people generally have an absolutely shockingly poor knowledge of what constitutes healthy portion sizes, good quality food, amount of calories in different foods! You just do you and poo poo to all the naysayers, it’s your life!

Oh and believe me I speak from experience, my sister is quite sanctimonious about all this to the point where my mum and I talk privately about it because we can’t be bothered arguing with her!

Flo x