3. November 2026

Fasting 101

Why we fast

For most of human history, food wasn't available around the clock. We evolved to move between two states, fed and fasted, and our genes still carry that programming. Today we can eat whenever we want, day or night, and that mismatch is a big part of why cardiometabolic conditions such as obesity, fatty liver, type 2 diabetes and high blood pressure have become so common.

Fasting simply reactivates a switch that's already built into us. Our bodies know what to do with it.

What actually happens when you fast

In the fed state, insulin rises to move glucose into your cells for immediate energy, and anything left over gets stored as fat. While insulin is circulating, fat burning is paused.

In the fasted state, insulin and blood glucose drop, stored glycogen is used up, and the body flips a metabolic switch: it moves from burning glucose to burning ketones and free fatty acids, including stored body fat. This is the mechanism behind most of fasting's benefits: improved insulin sensitivity, lower inflammation, better metabolic flexibility, and support for weight, mood and cognition.

Ketosis: once glycogen stores run low, usually somewhere between 12 and 16 hours into a fast, the liver starts converting fat into ketones, a backup fuel your cells (including the brain) can run on when glucose is scarce. This is ketosis, a completely normal metabolic state, not a crisis response. Ketones are an efficient, clean-burning fuel source, and many of the mental clarity and energy benefits people report while fasting come from the brain running on ketones rather than fluctuating blood glucose. It's also what drives fat loss during a fast, since the body is now pulling energy from stored fat to make those ketones. On top of that, one of the main ketones the body produces, beta-hydroxybutyrate, directly dampens down one of the body's key inflammatory pathways, which is part of why fasting and ketosis are linked to lower overall inflammation.

Autophagy: think of it as the body's cellular clean-up crew. Cells are constantly identifying old, damaged or malfunctioning parts, proteins that have misfolded, worn-out cell structures, and breaking them down so the components can be recycled into new, usable material. It's happening at a low level all the time, but fasting ramps it up considerably, which is why it's linked to cellular repair, anti-ageing effects, and a lower risk of the diseases associated with accumulated cellular damage. It needs a genuinely fasted stretch to properly switch on, which is part of why the longer fasts later in this talk carry benefits that daily TRE alone doesn't fully reach.

Who shouldn't fast, or should check in first

• Pregnancy or breastfeeding, nutritional needs are higher and more constant during this time
• A history of disordered eating, fasting protocols can be genuinely risky ground here, regardless of the framing
• Being underweight or already in a calorie deficit, extending fasting windows on top of that isn't appropriate
• Certain medications, particularly for diabetes or blood pressure, some need to be taken with food, and timing changes should go through a GP or prescriber first, not adjusted independently

Time-restricted eating (TRE)

Time-restricted eating (TRE) is the gentlest and most sustainable form of fasting, and it's the one I recommend as a daily practice. The two things that matter more than the number of hours are:

• When your fasting window starts
• When you break it

Start the fast early in the evening. Have your last meal as early as is realistic, ideally with a couple of hours to digest before bed. Digestion slows right down in the evening as the body prepares for sleep, so eating late means your stomach is still working hard well past midnight, cutting into the 7 to 8 hours of downtime it needs to repair its lining. The “Types of fasts” section further down has the full research and the digestion maths behind this, if you want the detail on hand for questions.

Break the fast within 2 hours of waking. This is the piece people most often get wrong, because a lot of fasting advice says “push breakfast back as long as you can.”

Here's why we don't do that:

• Cortisol: cortisol naturally rises in the first 30 to 45 minutes after waking as part of your normal wake-up rhythm, that's meant to happen and eating doesn't stop it. What eating does affect is what happens next: going too long without food afterwards is linked to a more dysregulated cortisol pattern through the rest of the morning, rather than it settling back down as it should. This is an unnecessary extra stressor for a lot of people, especially anyone dealing with fatigue, burnout or a nervous system that's already under load. Coffee on an empty stomach adds to this, caffeine itself triggers a cortisol release, so having it before food, on top of an already-elevated waking cortisol level, pushes it higher still, another reason to have coffee after breakfast rather than before.
• Pancreas readiness: research shows the pancreas responds better to food starting around 2 hours after waking and for the following 6 to 7 hours, with a noticeably better glucose response than later in the day. Delay it much longer than that and you lose that window. One controlled feeding study found that front-loading calories into breakfast and lunch for a week lowered mean glucose levels and increased insulin secretion, while skipping breakfast altogether produced a higher glucose response at the next meal and led people to snack more in the evening, exactly the pattern we're trying to avoid.
• Spleen Qi (Traditional Chinese Medicine): in TCM, the Spleen and Stomach are considered strongest between roughly 7 and 11am. This is the body's natural window for transforming food into usable energy (Qi). Eating within it works with that rhythm; skipping it and eating much later asks an already-taxed system to catch up, which over time can contribute to the fatigue, brain fog and poor digestion associated with Spleen Qi deficiency.

Fasting 16 hours Every Day: what to know and watch for

Perhaps some of you have read that going past 12 to 14 hours daily, long-term, carries risks, and it's worth addressing or perhaps you haven’t and wear your daily 16gr fast as a badge of honor?

Dr Valter Longo, the researcher behind the Fasting-Mimicking Diet, has been outspoken on this point: he argues that people who fast 16 to 18 hours a day, every day, roughly double their risk of needing their gallbladder removed compared to those fasting 11 – 14 hours, and that this pattern usually involves skipping breakfast, which in his view carries its own links to shorter lifespan and higher cardiovascular disease risk. His own long-standing daily recommendation is a 12-hour eating window, stretching to 13 – 14 at most.

The mechanism: the gallbladder only empties fully when it's triggered by a hormone released after eating. Left fasted too long without that trigger, bile sits and stagnates, and that stagnation is what allows cholesterol to crystallise into stones. This is the same reason rapid weight loss and very low-calorie diets carry a similar gallstone risk, it's about how long the gallbladder goes without being triggered to contract, not fasting itself being inherently harmful.

Here's the important distinction for this week: Longo's concern is specifically about 16 hours becoming someone's permanent, daily pattern, indefinitely, often alongside habitual breakfast-skipping. A structured, supervised 16-hour window for the duration of a retreat is a different proposition, closer to the short-term, purposeful use he himself says is reasonable when there's a clear goal and a defined end point.

Types of fasts, and how to approach each

Fasting can be relatively easy to slot into your daily routine. Depending on the outcome you are striving for, there are several fasts to try. Time restricted eating which is ideally timed with your circadian rhythm for maximum benefit, a weekly 24-hr water fast, a 36-hr water fast, a 3-day water fast (this is best done under supervision) and the five-day fasting mimicking diet.

Research into fasting is ongoing and has a long list of reported health benefits. Most of the studies focus on time restricted eating (TRE). TRE is a type of intermittent fast that incorporates an overnight fast and usually an 8 / 10 / 12 hour eating window every day. As mentioned above, there are differing opinions on how long the fasting duration should be. Some experts recommend leaving as long as is comfortable between dinner and breakfast. Some even recommend that you miss breakfast altogether and just have lunch and dinner – mix it up.

There is clear data indicating that the time of day you eat, and the length of your fasting window can help with weight loss, blood pressure, insulin resistance, glucose response, energy levels, improvements in the microbiome and your overall mood. There are also clinical studies being carried out looking at autophagy, stem cell regeneration and cancer support with initial results looking promising.

Based on the research on time restricted eating, the data indicates that it is important to give yourself a minimum fasting window of 12-hrs every day and ideally have your last meal/snack at 7pm. When you take into consideration our bodies 24-hr circadian rhythm this type of meal timing makes a lot more sense. In the evening the body prepares to go to sleep, melatonin is released a couple of hours before bed, digestion slows down (acid secretion, digestive juices, insulin secretion) and every organ in the body gets ready for some downtime.

Eating out of alignment of your circadian rhythm will affect your insulin secretion and when this is compromised it can spike your glucose levels (as our bodies cannot process the glucose properly). If this is a regular occurrence it could eventually lead to type-2 diabetes and fat storage. In the evening, how the food moves through our intestines also slows down and the next day it can feel like the food hasn't been digested properly - it actually hasn't.

The simple math from the stomach's point of view is:

• It takes approximately 5-hours to digest a good-sized meal, so if you have your dinner at 8pm the stomach will continue to work for the next 5-hours. This means that at 1am in the morning our digestive system finally gets ready to have some downtime to repair and reset.
• The stomach needs about 7 – 8 hrs downtime every night to repair the stomach lining - triggered after 7-hours without food. So, eating at 8pm followed by 5-hours to digest, followed then by 7 – 8 hrs of repair, means that it would be beneficial to abstain from eating until 9am the next day.

Studies comparing time restricted eating windows - early versus later in the day - assessed if the same benefits were reported regardless of the time. They also investigated how long was best to wait to have breakfast after you woke up.

The results revealed something we have all heard before - eat breakfast like a king, lunch like a prince and dinner like a pauper. Eating like this saw improvements in weight loss, blood sugar control, appetite suppression and fertility.

Earlier time restricted eating at 8am to 4pm compared to midday to 9pm was reported in 75% of the studies to have the biggest improvement on glycaemic control (our overall blood glucose response during the day) and blood pressure. A Japanese study also reported greater insulin sensitivity, lower inflammation and greater diversity in the microbiome when adhering to the earlier window.

Time-Restricted Eating (TRE) is the daily overnight fast timed with your body clock, the 16-hour version is what we're running this week, though most guests will find a 12 to 14-hour version more realistic and a safer long-term approach when you’re home. It's the gentlest entry point, lowers insulin levels every day, and supports digestion without requiring any special preparation. If anyone plans to keep skipping breakfast daily once home, flag that fitting all their protein, fibre and micronutrient needs into two meals instead of three takes real planning, it's easy to under-eat protein or miss key nutrients when the eating window shrinks, so this isn't something to do carelessly long-term.

24-Hour Fasts run from dinner one night to dinner the next, so you sleep through a large chunk of it and it barely disrupts family life. Benefits include gut repair, a switch into ketosis, lower blood pressure and inflammation, better insulin balance, and the start of autophagy, your body's cellular clean-up process, which switches on around the 17-hour mark. This is a step up from TRE, best done once a week rather than daily, and it's worth mixing with shorter fasts so your body doesn't adapt to the same pattern every time

3-Day Water Fasts extend those same autophagy and cellular repair benefits much further, autophagy continues climbing through this window, and by 72 hours the body has shifted heavily into a deep repair and immune-reset state. This is a bigger undertaking than the fasts above and should be approached with more care: build up to it with shorter fasts first, keep electrolytes up throughout, and ideally do it under supervision rather than attempting it solo the first time.

The Fasting-Mimicking Diet (FMD) is a 5-day protocol developed by Dr Valter Longo, using a low-calorie, low-protein, low-carbohydrate approach that tricks the body into a fasted state while you're still eating small amounts of food. It's designed for people who find water-only fasting too extreme, and it delivers many of the same benefits, cellular clean-up, reduced inflammation, stem cell stimulation, without the intensity of going without food entirely. This is the protocol behind the supplements and supported eating you'll be doing here this week, approach it as a structured, guided reset rather than something to freestyle, since the calorie and macronutrient targets are specific for a reason.

Vitamin C is included on the FMD because such a low-calorie, restricted intake makes short-term micronutrient shortfall likely, and even a mild dip can worsen fatigue and low mood, symptoms clients are already prone to on a fast. Vitamin C also acts as a water-soluble antioxidant, helping offset the rise in reactive oxygen species that comes with the fasting-to-ketosis shift, supports normal immune function during a period when intake is much reduced, and acts as a required cofactor for collagen synthesis, which matters once refeeding kicks the body back into rebuild mode.

Electrolytes (sodium, potassium) are included because carbohydrate restriction lowers insulin, and lower insulin causes the kidneys to excrete more sodium, taking water and potassium with it. This is the main driver of fasting headaches, light-headedness, and fatigue, so replacing electrolytes helps prevent those symptoms rather than treating them after the fact.

Magnesium is included because it is lost alongside sodium and potassium through the same kidney mechanism, and it plays a role in energy production, muscle function, and nervous system regulation, all relevant given clients are running on very low calories. Low magnesium during fasting is a common contributor to muscle cramps, headaches, and disrupted sleep, so keeping it topped up helps clients tolerate the 5 days more comfortably.

It's worth mixing up which of these you do week to week rather than settling into one fixed pattern. The body responds better when it can't fully predict what's coming, this is hormetic stress at work, a small, manageable challenge the body has to adapt to, which is what makes it beneficial rather than harmful. Doing the exact same fast every single week gives the body nothing new to adapt to, so varying the type, length and timing keeps that adaptive response switched on.

What breaks the fast

Anything that stimulates digestion or provokes an insulin response breaks the fast. Herbal tea is fine on an empty stomach; if you want coffee or black tea, it's kinder on the gut to have it after breakfast rather than on a completely empty stomach.

Common mistakes to watch for

A few things that trip people up during a week like this:

• “It's just a splash”, milk or cream in coffee, a spoon of honey, a couple of berries, these still contain calories and protein and will break the fast, even in small amounts
• A few nuts or a bite “doesn't count”, it does, anything that triggers an insulin response counts, regardless of portion size
• Breaking a longer fast with a big or heavy meal, after 24 hours or more, a large meal can cause real digestive discomfort, bloating and nausea, ease back in gently rather than making up for lost time in one sitting
• Under-hydrating, thinking water and electrolytes only matter during the eating window, if anything they matter more while fasting
• Treating the eating window as a free-for-all, a shorter window doesn't cancel out the quality of what's eaten within it, this is still about nutrient-dense food, not just timing

Breaking the fast well

How you break a fast matters as much as the fast itself.

• Eat slowly, chew well, don't overload the digestive system straight away
• Favour cooked foods over raw to start with, raw food is more taxing to digest after a fasted stretch
• Include protein, healthy fats, and some prebiotic and probiotic foods to support the microbiome
• Good options: eggs or a protein of your choice with avocado, sauerkraut and olive oil, a warm smoothie, or a simple soup

A note on individual variation

Fasting isn't one-size-fits-all. Adherence matters more than perfection. We'll be checking in with each of you individually, and if anyone has questions about how this interacts with their own health picture, that's exactly what our one-to-ones are for.