From reducing inflammation to improving brain health, The Fast 800 diet expert explains the benefits of a keto diet and 5 easy ways to 'flip the metabolic switch'

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Did you know that your body is like a hybrid car? It runs on two main energy sources: glucose and fat. Interestingly, we don’t need to rely on glucose (sugar); more and more research now points to fat being a far more efficient form of energy.

Switching from using glucose to fat (or ketones) as your fuel source is what I call 'flipping the metabolic switch'. This is when your body begins to burn fat efficiently, triggering weight loss. This process is also known as going into 'ketosis'.

In December 2021, I completed a week of The Fast 800 Keto. I lost 2.2kgs (nearly 5lb) and 2cms around my waist. My blood pressure went down by 10 points into the super healthy range and my early morning fasting blood sugars dropped from 5.6 (borderline prediabetic) to 4.6 (super healthy). All in seven days.

This is how our 'dual fuel' system works. The body prioritises burning glucose (sugar) if it’s available - for example when we eat carbohydrate-rich foods such as bread, potatoes and pasta. It burns sugar first, fat second. However, fat is a far more efficient source of energy, and switching from using glucose to using fat as your fuel source can lead to a host of benefits such as weight loss, feeling less hungry, having more energy and a clearer mind.

When we limit our consumption of carbohydrates and instead enjoy a diet that prioritises healthy fats and protein, dietary fats are converted into something called ketone bodies by the liver and used as fuel. This is known as going into ketosis. You are using your body’s second, more efficient source of fuel. It’s like switching your car from petrol to electric.

What exactly is ketosis and what are the health benefits?

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 to 12 hours after eating, your body turns to fat as an energy source. It flips the metabolic switch. Your liver then converts that fat into ketone bodies, which the body uses as fuel.

The first fat to go is likely to be around the tummy. Having lots of fat stored around the tummy is really unhealthy, which is why your waist size is such an important predictor of health. You also start to rapidly lose any fat that has been stored in your liver and pancreas, which is again a really bad place for it to be. That is why people with raised blood sugars see rapid improvements.

You can achieve ketosis through reducing your carbohydrate intake (nutritional ketosis) or through incorporating intermittent fasting/Time-Restricted Eating  (fasting ketosis).

Not only is ketosis helpful for good for weight loss, but your brain also runs better on ketone bodies as fuel than glucose. Ketones stimulate the production of BDNFs (brain-derived neurotrophic factor) protein that creates new brain cells and brain cell connections.

Why do too many carbs make you gain weight?

When we eat high carb meals, the body breaks them down into glucose, causing blood sugar levels to rise. Your pancreas releases insulin to help the body to use the sugar as fuel. This rapidly reduces your blood sugar levels, and any glucose not used for immediate energy is stored as glycogen. Once your glycogen stores are full, excess glucose is stored as fat, meaning we gain weight.

What’s more, with more sugar in your blood, the pancreas makes more insulin to help distribute the glucose. This becomes a vicious cycle called insulin resistance, which can lead to developing type 2 diabetes. I developed this condition myself but was able to reverse it by switching to a more Mediterranean style of eating that prioritizes proteins and healthy fats and eating within a set window (time-restricted eating or intermittent fasting).

How does a ketogenic diet makes you less hungry and improve energy?

When you go into a state of ketosis, this stops your body from producing a hunger hormone called ghrelin. Normally when you lose weight your ghrelin levels start to rise. Not when you are in ketosis. This is true of men and women.

Ketones are a very 'clean' fuel which is why your brain and body thrive on them and you feel sharp and energetic.

Is a keto diet safe?

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.

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 and potentially reverse the condition. While the participants in these trials struggled to maintain a ketogenic diet long-term, the short-term application for rapid weight reduction, improved blood sugars and other metabolic markers is promising.

We have created Fast 800 meal plans as an accelerated method of falling into nutritional ketosis and keeping you there. It's for 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.

How long can you follow a Fast 800 Keto plan?

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.

If you have previously followed 12 weeks of a calorie-restricted diet (such as 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, for example, The New 5:2 for long-term results.

5 ways to flip the metabolic switch

When you flip the metabolic switch, either by intermittent fasting or reducing carbohydrates,  it can take anywhere from a few days to a few weeks to begin seeing the benefits. Here’s how to make it happen.

1. Try intermittent fasting or time-restricted eating

Give yourself a window when you are not eating. The easiest way is overnight. Start with 12 hours of not eating, say 8pm to 8am and then increase to 14 or 16, known as the 16:8, that is – 16 hours of fasting and eating usually two meals within an eight-hour window.

Why 12 hours or more? When we deplete our stores of glucose – by not eating – our bodies then turn to glycogen, the alternative form of glucose that’s stored in your muscles and liver. You have about 500g of sugar stored as glycogen in your muscles and liver. When these stores start to run low your body turns to fat as its main fuel source. This is known as 'flipping the metabolic switch'.

2.  Make carb swaps

Remember your body is primed to first burn up glucose before it gets to work on burning fat. So by eating a low carb diet your turns to burning fat sooner. My advice is to cut down on soft drinks, sweets, rice, potatoes, bread and fruit juice and choose non-starchy vegetables, whole grains and legumes. A low carb diet doesn’t mean it’s a no-carb diet. There’s room for plenty of low carbohydrate vegetables.

Reduce your intake of the following:

Simple carbs – like juices, fruit, sugar and sweet things are broken into glucose quickly and cause a rapid rise in blood sugar levels.

Starchy carbs – found in potatoes, rice, wheat, bread, corn – similarly to simple, cause a rapid rise in blood sugars.

And opt for these carbs instead:

Complex carbs – found in vegetables, take longer to digest meaning there’s a more gradual rise in blood sugars.

Fibre – a form of complex carbs that is non-digestible, it feeds the gut microbiome and supports healthy digestive function.

For example, the easy  Fast 800 Salmon Sushi recipe  is a simple but impactful food flip. Conventional sushi is made from rice which is carbohydrate loaded, while this alternative version is protein-rich, sustains for much longer and enables the body to burn it as a fat fuel source. If you use cauliflower rice mixed with cream cheese to give that ‘sticky’ texture you’ve ‘flipped the metabolic switch’.

Once you’ve grasped the simple concept, you can apply the idea to many of your favourite foods

MORE GLOSS: Make the Fast 800 Keto Diet Mediterranean Pizza 

3. Follow the 50:50 rule

As well through intermittent fasting, you can achieve ketosis by reducing your carbohydrate intake (nutritional ketosis). In my book The Fast 800 Keto , I recommend following the rule of 50:50. Keep carbohydrates under 50g per day and ensure protein remains above 50g.

4.  Follow a Mediterranean-style diet

If you choose rich in protein, fibre, healthy fats and some complex carbs, you can flip your metabolic switch while reaping the benefits that come with, what studies say may be the healthiest diet out there. On the Fast 800 plan, we encourage daily consumption of vegetables, fruits, whole grains and healthy fats, weekly intake of fish, poultry, beans and eggs and moderate portions of dairy products and limited intake of red meat

4.  Give yourself time

It can take anywhere from a few days to a few weeks to flip the metabolic switch and begin seeing the benefits. By continuing to follow meal plans provided, you’ll be on track. Trust the science, stick with it and you absolutely will see progress.”

Dr Michael Mosley is founder of The Fast 800 weight loss plan that embraces time-restricted eating, the Keto diet and the Mediterranean principles of consuming a diet rich in healthy proteins and vegetables and lower in carbs.

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