16:8. 5:2. Alternate days. Three day water fasts.
If you’re trying to work out which version of fasting, if any, is right for you, you’re in the right place, and the honest answer is, it depends.
Fasting has been practised for health, religious beliefs and spiritual reasons for thousands of years. More recently, it has gained serious traction for its potential weight loss, blood sugar and metabolic health benefits.
As Registered Nutritional Therapists, we sit with people every week in clinic who’ve tried fasting, loved it, broken on it, or simply don’t know where to start.
If you’d rather not puzzle this out alone, you can book a free 20-minute call and we’ll tell you, in plain English, whether fasting is likely to help or hinder for your particular biology, stage of life and goals.
What is fasting?
Fasting simply means abstaining from food, drink, or both. Most fasts restrict food while allowing water, black coffee and tea. It is different from calorie restriction or selective eating.
In other words: it’s about when you eat, not just what.
There are three stages. The ‘fed state’ is the first hours after eating. The ‘early fasted state’ runs from 3 to 4 hours up to 18 hours after eating. The ‘fasted state’ kicks in beyond 18 hours. Most popular fasts sit in those first two stages, and the deeper benefits, like switching fuel sources and improving insulin sensitivity, come from getting better at moving between fed and fasted, not from extreme deprivation.
The most popular forms of fasting
- Alternate-day fasting: significantly reduced calorie intake (0 to 400 kcal) every other day, with unrestricted eating on non-fasting days.
- 5:2 diet: two reduced-calorie days each week, with unrestricted eating on the remaining five.
- Time-restricted feeding: all meals consumed within a set daily window (8 to 10 hours), fasting for 14 to 16 hours. Often called ’16:8′ or ’14:10′.
- Periodic fasting: limited calorie intake over multiple consecutive days, for example three days a month, mimicking the effects of fasting while still allowing some food.
In our clinic, by far the most realistic and sustainable for the average client is the gentler end of time-restricted feeding: a 12 to 14 hour overnight fast, which simply means finishing dinner earlier and not snacking before bed. It supports blood sugar balance without tipping people into the hormonal stress that longer fasts can trigger.
The benefits of fasting
Like every health strategy, fasting comes with benefits and drawbacks. What works beautifully for one person can backfire for another.
Here are the upsides the research consistently points to, and which we see show up in clinic when it’s the right fit:
- Weight loss and fat burning, through reduced calorie intake and improved insulin sensitivity.
- Improved cardio-metabolic health: lower blood sugar, better insulin sensitivity, lower blood pressure, cholesterol, triglycerides and inflammation markers.
- Gut health: improved microbiome diversity to support digestion.
- Autophagy and cellular repair: cellular clean up that may lower chronic disease risk.
- Brain health and mental clarity, via raised BDNF and potential neuroprotective effects.
- PCOS benefits: women using an 8-hour daytime eating window have seen improved menstrual cycle regularity.
Drawbacks and who should be cautious
Fasting is not for everyone, and pretending otherwise is what gets people into trouble.
The drawbacks we watch for in clinic are:
- Stage of life: symptoms can worsen for women in perimenopause and menopause as oestrogen falls.
- Thyroid conditions: longer fasts can complicate symptoms and medication timing.
- Hunger, energy dips and mood swings for newer fasters. Gradual increases are essential.
- Muscle loss risk if protein intake or strength training are inadequate, which means fasting burns muscle instead of fat.
- Blood sugar fluctuations and hypoglycaemia risk for those with type 2 diabetes or on glucose-lowering medication.
- Rebound overeating or poor food choices after a long fast, which undoes the benefit.
Women and men respond differently. It matters.
Men and women are biologically different and need to approach fasting differently. This is the single biggest reason we see fasting fail in clinic: women copying men’s protocols, or following internet advice that completely ignores the menstrual cycle, perimenopause, thyroid history and exercise pattern.
For women, the headlines are: hunger-related neuropeptides rise with fasting, hormonal health depends on regular nutrient-dense meals, and low energy availability can disrupt cycles, fertility, bone health and metabolic rate. New fasters should start with a gentle 12 to 14 hour overnight fast, avoid multi-day periodic fasting, and adjust hours around the menstrual cycle. Fasted exercise tends to backfire for midlife women, so eat first and refuel within 30 to 45 minutes. Pregnant and breastfeeding women should not fast.
For men, short-term fasting can boost growth hormone, but longer-term fasting can reduce testosterone if nutrient needs aren’t met. Some report sharper focus; others feel fatigued and irritable. The rule is the same either way: listen to your body, and don’t push through symptoms.
If this section is the bit where you’re thinking “I have no idea which of these applies to me”, that is exactly the point where personalised support saves you months of trial and error. A one-off wellness check gives you a clear, written plan: whether to fast, how long, when, around your cycle and around your goals.
If you’re ready to try fasting, just remember
- Nutrition matters: build meals around protein, healthy fats and complex carbs.
- Hydration: at least 2 litres of water or herbal teas daily.
- Exercise timing: midlife women generally do better on fed workouts, refuelling within 30 to 45 minutes. Men can often break their fast post-exercise instead.
- Be mindful: fasting can increase cravings and lead to rebound overeating.
- Medical advice: speak to your GP first if you have diagnosed conditions or are on regular medication.
In a world where we can eat 24/7, intermittent fasting offers a way to restore your routine and reduce unplanned grazing, especially in the evening.
Our clinical bottom line: for most people, a 12 to 14 hour overnight fast supports weight loss, blood sugar balance, gut health and long-term cardio-metabolic wellbeing without the downsides of more aggressive protocols.
Confused about food? Three ways we can help
Searching the internet can be a vortex of conflicting advice that leaves you more confused than when you started. Personalised nutrition is the only honest answer. Pick the rung that matches where you are right now:
- Read more about blood sugar, the engine behind fasting’s biggest wins: the cardio-metabolic blog cluster explains why your blood sugar, cholesterol and blood pressure are really the same problem.
- Get the picture, then a plan: a one-off wellness check gives you full bloods, a deep clinical review and a written plan, including whether and how fasting fits for you.
- Ready for proper support: our blood sugar and insulin resistance programme takes you from confused and craving-led to steady, with hands-on guidance from a Registered Nutritional Therapist over 3 or 6 months.
Not sure which rung? Book a free 20-minute call and we’ll point you to the right one. No hard sell. We will tell you honestly whether fasting is for you, and what to try first if it isn’t.
