16th April 2023

How To Do The Fast 800 Keto Diet

The Fast 800 Keto is different from your typical high fat, low carb ketogenic diet. The Fast 800 Keto builds on the science that provides the foundation for The Very Fast 800 and simply reduces the carbohydrates even further to push your body into more consistent nutritional ketosis.

What is a keto diet?

A ketogenic (‘keto’) diet is a high fat, low carbohydrate diet that puts your body into the metabolic state of ‘ketosis’. It involves efficiently burning fat as your body’s main energy source, rather than burning glucose which is most commonly found in carbohydrates; this process is known as ‘flipping the switch’. There are many health benefits of following a keto diet, such as weight loss, lowered risk of various diseases and improved insulin sensitivity, to name a few.

What is ketosis?

Ketosis, in basic terms, is the metabolic state that occurs when your body doesn’t have enough glucose from carbohydrates to burn for energy. When this happens, your body seeks energy in the form of glycogen (glucose stored in your muscles and liver). When glycogen stores run low, around 10-12 hours after eating, your body turns to fat as an energy source. During ketosis, fat is turned into ketone bodies in the liver. These are then released into the bloodstream and generate energy until we begin eating carbohydrates again.[1]

You can achieve ketosis through reducing your carbohydrate intake (nutritional ketosis) or through incorporating intermittent fasting/Time-Restricted Eating (fasting ketosis). Here at The Fast 800, we offer options for both, depending on what’s achievable for you.

Is a keto diet difficult to follow?

A traditional keto diet can be restrictive, as it’s very low in carbohydrates and high in fat. Cutting out carbohydrates isn’t as simple as avoiding pasta or bread, it also involves the restriction of certain vegetables, legumes and beans as well, which many find difficult to avoid.

There are also a number of undesirable side effects that can come with the traditional diet, such as headaches, insomnia, nausea and vomiting, and dizziness[2]. This can be referred to as the ‘keto flu’, and often makes it feel hard to stick to the diet. 

Additionally, although a keto diet can result in rapid weight loss, people often find that they have a ‘yo-yo’ effect, finding difficulty in keeping the weight off long-term. It’s been suggested that there is a period of increased glucose sensitivity following a period of having a very long carbohydrate diet, so a transition phase from a strict keto diet to regular diets are recommended.[3] One such transition diet would include The Fast 800 Way of Life plan so, if you’ve been following an alternative keto diet and are looking to slowly increase your carbohydrate intake, we recommend looking further into this approach.

How is The Fast 800 Keto different?

The Fast 800 Keto is different from your typical high fat, low carb ketogenic diet. It was designed to combine the keto principles with a Mediterranean diet, allowing you to enter ketosis, while still reaping the benefits of one of the healthiest diets out there. The Fast 800 Keto builds on the science that provides the foundation for The Very Fast 800 and simply reduces the carbohydrates further to push your body into more consistent nutritional ketosis.

The Fast 800 Keto is slightly higher in carbohydrates than a traditional ketogenic diet, as we combine a keto diet with a lower calorie diet (around 800-1000 calories a day), but it is still considered a ‘very low carb’ diet. For many, this can make it easier to follow and sustain, with fewer side effects yet brilliant weight loss and health benefits. 

The main differences between a traditional keto diet and The Fast 800 Keto diet, is that ours is: 

  • Slightly higher in carbohydrates
  • Lower in saturated fats
  • More focused on quality protein
  • Filling and nutrient-dense (with Mediterranean-style meals created by our in-house nutritionist)

Our Online Programme has meal plans that cater to three and two meals a day which ensure that you’re getting the right nutrients you need from meals that are lower in carbohydrates, which is often difficult to calculate yourself. The recipes we provide are not only nutritious, but delicious too, which helps with sticking to the approach for as long as needed (maximum 12 weeks).

What foods to eat on The Fast 800 Keto Diet

If you’ve read Dr Mosley’s book, The Fast 800 Keto, you’ll know that he recommends following the rule of 50:50. Keeping carbohydrates under 50g per day and ensuring protein remains above 50g.

For the Online Programme, we have developed keto meal plans to align with the principles of the best-seller, where calories fall between 800-1000 each day. The meal plans have been carefully designed to ensure you consume at least 50-60g of protein and around 20g or less carbohydrates. Our carbohydrates are significantly lower than Dr Mosley’s recommendations to allow you to add extra low-calorie, non-starchy vegetables to every meal, without having to worry about counting extra carbs.

If you’re looking for options with slightly higher carbohydrates and a greater focus on calorie restriction then The Very Fast 800 meal plans may be a better choice; The Very Fast 800 and plans including fasting days are similar to this, however, you have slightly more carbohydrates at around 50g or less per day (still considered low-carb) and the rest is healthy fats.

Alternatively, if you’re not looking to lose weight rapidly, and are looking for more gradual, and sustainable weight loss with improved metabolic health, The New 5:2 or Way of Life approaches are fantastic options.

Whichever plan we recommend for you when you take the personalisation questionnaire after signing up to the Online Programme,  we always ensure you’re getting in enough of these foods and nutrients:

Protein: Our meal plans are designed to ensure you consume at least 50-60g of protein a day. This is because protein plays an essential part in ensuring you stay fuller for longer on a low carb keto diet, and helps maintain muscle mass while losing weight.[4] Animal proteins such as fatty fish (like salmon, mackerel and sardines), quality meat and poultry, and eggs are all keto-friendly.

Fibre: Fibre is essential for a healthy gut microbiome and often lacking in traditional keto diets. It is digested by bacteria that have been linked to the prevention of weight gain and chronic illnesses like type 2 diabetes, heart disease and some cancers.[5][6] While high fats like the ones you consume in a keto diet slow digestion, fibre can help support your gut system. Foods like broccoli, cauliflower, and leafy greens are all excellent sources of fibre that should be eaten plentifully in The Fast 800 Keto plan.

Healthy fatsHealthy fats are an essential way of providing energy for your body to run on, instead of carbohydrates. Olive oil is a healthy fat staple in a Mediterranean-style diet, and is no different for a keto diet. It’s a monounsaturated fat which has shown to hugely benefit the heart, decreasing the risk of heart disease.[7] We also love to promote the benefits of Greek yoghurt as a healthy fat for plenty of reasons, and it is particularly beneficial on a keto diet as it has been shown to increase feelings of fullness and is thought to decrease intake of unhealthy foods.[8]

What does The Fast 800 Keto Diet Plan Look Like

Benefits of a keto diet

Keto diets have been around for hundreds of years. Originally created to help those with epilepsy by reducing the brain’s need for glucose as fuel, therefore slowing the misfiring that causes seizures.[9] The benefits of a keto diet on the body and mind are extensive, so here are just a few:

  1. Rapid weight loss: One of the main reasons people follow the diet today is to lose weight rapidly. Perhaps surprisingly to some, there is research that suggests people that follow a keto diet may lose more weight than people following a low-fat diet.[10] A low calorie keto diet, like The Fast 800 Keto diet is effective in preserving your metabolic rate and maintaining muscle mass at the same time as losing weight.
  2. May help manage type 2 diabetes: Research in recent years has found the keto diet to be effective for those with type 2 diabetes to help reduce central obesity, manage their blood sugar levels, reduce the need for insulin and potentially reverse the condition.[11] One study in people with type 2 diabetes found that carbohydrate-restriction had such a dramatically positive effect on glycemic parameters that they are campaigning for it to be implemented instead of medication.[12] Another study found that 95% of people with type 2 diabetes had reduced or eliminated their glucose-lowering medication within six months.[13]
  3. Reduces risk of chronic disease: A keto diet has been linked with reducing the risk of multiple chronic diseases, perhaps mostly due to a low-carb diet’s ability to lower blood pressure. For example, it has been shown to reverse metabolic syndrome, and lower the risk of cardiovascular disease and Alzheimer’s to name a few.[14][15]
  4. Improves gut health: There are recent studies that suggest a keto diet is beneficial to the body’s gut microbiome. Though there is not much research on the long-effects of a keto diet on the gut microbiome, some studies suggest that it may increase the genetic diversity of microbiota by improving insulin resistance, dyslipidemia and inflammation.[16]
  5. Suppresses appetite: A keto diet is known to suppress hunger and reduce appetite.[17] This is potentially due to the higher satiety effect of protein. Studies also show that when people cut carbs and eat more protein and fat, they end up consuming far fewer calories.[18] A low carb, high fat, high protein diet like The Fast 800 Keto diet that helps to suppress appetite can therefore make it easier to stick to a low calorie diet longer term, reduce cravings and help you feel fuller for longer.
  6. Helps reduce visceral fat: Visceral fat is often known as a ‘hidden’ fat, as it is stored deep within the abdominal cavity of the body, wrapping around organs such as the liver and intestines. It’s particularly dangerous as it’s difficult to see or feel, and has been linked to a raised risk of various chronic illnesses and shorter life expectancy[19]. Research has recognised that a keto diet may help people to lose 3 times more visceral fat than those on just calorie restriction. Similarly, studies have shown that following a keto diet helps to reduce visceral fat much more than a low-fat diet.[20]

In December 2021, Dr Mosley completed 7 days of The Fast 800 Keto, here are his results: 

“In just 7 days I’ve lost 2.2kgs, 2cms around my waist, my blood pressure has gone down by 10 points into the super healthy range and my early morning fasting blood sugars have dropped from 5.6 (borderline prediabetic) to 4.6 (super healthy). All in seven days!”

– Dr Michael Mosley

There is compelling evidence that when you use a keto meal plan, you go into ketosis faster, and begin to burn more fat. However, it can be difficult with such restriction, which is why it’s not for everyone. The Fast 800 Keto reinforces everything that we believe at The Fast 800 and does not undermine the science behind The Very Fast 800. The Fast 800 Keto may not be for everyone but is something you may wish to explore. 

Tips for following a keto diet

  • Meal prep: You know what they say: fail to prepare, prepare to fail. It may not be as black and white as that, but meal prepping your food in advance can help save you time and money. It can also prevent you from resorting to high-carb foods if you’re caught without time to cook a healthy meal
  • Freeze meals: Similarly to meal prepping in advance, freezing your meals can help make sure you have healthy, keto-friendly meals ready. We have a range of recipes available on The Fast 800 Keto plan that are easily freezable and taste just as good after reheating as the day you made it!
  • Drink plenty of water: The state of ketosis may cause some people to feel thirstier than usual. Once you drastically reduce your carb intake, your body starts processing electrolytes differently and can cause dehydration. Some research even suggests that keto diets increase the risk of developing kidney stones in dieters who aren’t drinking enough water.[21] So, make sure you’re staying hydrated and healthy.
  • Have a helpful meal plan: With a diet as restrictive as the keto diet, having a meal plan of delicious recipes can help keep you inspired and motivated. A plan will also ensure you’re getting the right amount of nutrients you need to successfully reach your goals, keeping you energised and full. Our Online Programme even includes a convenient weekly shopping list for The Fast 800 Keto plan so you know what to buy ahead of time.
  • Load with veggies: You now know the importance of nutrients like protein, healthy fats and fibre: loading up with non-starchy, keto-friendly veggies is key to successfully following a keto diet. They contain beneficial vitamins and minerals to keep your body and mind healthy, and can be eaten plentifully to ensure you’re full after every meal and don’t reach for unhealthy snacks later.


1. Who is The Fast 800 Keto for?

Our brand new keto plans have been developed for those who have a lot of weight to lose, and are ready and committed to make changes. People who are pre-diabetic or have type 2 diabetes could follow these plans (monitored by a GP) to improve their insulin sensitivity. A rapid weight loss plan, with typical weight loss of around 10kg in 12 weeks, is a proven way to reverse, and prevent the onset of, type 2 diabetes.

The Fast 800 Keto plans are not replacing The Very Fast 800 plans, they are simply an option for those that are looking for a little more and who are motivated to follow a very restrictive meal plan. If you decide you do not like this approach or would prefer more variety, you can switch to The Very Fast 800, or our other plans, at any time when you join the programme.

2. How long can The Fast 800 Keto plans be followed for?

We recommend that you follow The Fast 800 Keto plans for no more than 12 weeks. When you have completed this or attained a healthy BMI, move to The New 5:2 or Way of Life. We’re encouraging our current members to think of The Fast 800 Keto and The Very Fast 800 as interchangeable; you cannot complete 12 weeks on one, then 12 weeks on the other. It’s either/or, whichever works best for you. 

If you have previously followed 12 weeks of a calorie restricted diet (like The Very Fast 800) and have found that you have put on unwanted weight over a period of time, you can follow the keto plans for two weeks to kick start weight loss, before moving on to The New 5:2 for long-term results. 

3. Are there any products to support a keto diet?

Absolutely! We understand that it can often be difficult to achieve more than 60g of protein through diet alone, particularly when following a low calorie diet, and have created keto-friendly Protein Powders to make things a little easier – the Protein Powder should be enjoyed alongside your usual meals for an additional 20g protein per day. Unlike fats and carbohydrates, your body cannot store protein, which is why keeping up a good daily intake is so important to support metabolic health. 

Our Protein Powder is currently available in the UK, Australia and New Zealand and suitable for vegetarians and vegans. You can find out more about it here. 

4. Is a keto diet the only way to enter ketosis?

Eating a keto diet may be the most effective way to enter ketosis, but there is another way: intermittent fasting. Time restricted eating (TRE) is an eating pattern that involves fitting the time you spend eating into a particular window. For example, a 12:12 pattern is 12 hours of fasting with a 12 hour eating window. TRE has been recognised to speed up the process in which ketone bodies are produced, and assists with ‘flipping the switch’.

On The Fast 800 Online Programme, we provide plans for two and three meals a day, depending on what you’d like your eating window to be. Additionally, The New 5:2 diet involves two fasting days a week, and may induce mild ketosis. This can work well for people who are just getting started with intermittent fasting.

We have a full article on how to achieve ketosis without a strict keto diet here.

5. Do the new keto plans replace The Very Fast 800 plans?

No, the keto plans are simply an option for those feeling a little more ambitious and looking for accelerated weight loss.

The Very Fast 800 is still a valid approach, and more suitable for those new to low calorie diets, that will definitely kickstart your weight loss journey – it will most likely put you into a state of mild ketosis because you will be running down your sugar supply. You may find your body comes in and out of ketosis while following The Very Fast 800; being able to switch back and forth from using glucose and ketones as energy is a great skill to teach your body and helps it to become metabolically efficient. Due to the calorie restriction, you will still be losing weight. 

Essentially, The Fast 800 Keto is an accelerated method of falling into nutritional ketosis and keeping you there. If you’re looking to try out new keto meal plans, you can do so today by signing up to our 7 day free trial.

To summarise

Ultimately, if you’re wondering how to do The Fast 800 Keto diet, the answer is very simple: all you need to do is sign up to our Online Programme and follow our step by step guides. Our instructions are easy enough for anyone who is new to the diet to follow, and our recipes created by our in-house nutritionist are so delicious it won’t feel like you’re ‘dieting’. 

We have a community of people just waiting for you to join them, with support on hand from like-minded people if ever you need it. Our plans are goal-focused, whether your goal is to reduce risk of disease or to lose weight healthily and enjoyably. So, choose whichever plan works best for you, and don’t forget to write down your progress so you can see just how far it can take you!


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