Nutrition Advice – Fasting
As a Nutritional Therapist based, I frequently speak to people who are interested in fasting.
Perhaps they have heard that fasting can support weight loss, improve blood sugar control, give the digestive system a break, support detoxification or benefit the mitochondria. Or perhaps they simply skipped breakfast and wondered whether they were now “fasting”.
But fasting isn’t automatically beneficial simply because you haven’t eaten for a certain number of hours.
The more useful question is: why are you fasting, and is it appropriate for you?
From a naturopathic nutritional therapy perspective, I believe it is important to understand the reason behind fasting and to consider the foundations of health first. For some people, fasting may be a useful tool. For others, improving the quality and consistency of their diet may be far more beneficial.
What actually counts as fasting?
The word fasting is used to describe several different approaches, ranging from a simple overnight period without food to several days without calories.
This is important because these approaches are not interchangeable, and they can have very different effects on the body.
Fasting
In its strictest definition, fasting means deliberately abstaining from caloric intake for more than 24 hours.
Water is generally consumed during a fast, although some approaches allow drinks such as tea or coffee and the use of minerals or electrolytes.
Some experts reserve the term fasting for this type of extended calorie-free period and don’t consider intermittent approaches to be true fasting.
Intermittent Fasting
Intermittent fasting (IF) is a broad term used to describe eating patterns that alternate between periods of restricted food or calorie intake and periods where eating is unrestricted or less restricted.
There are several different ways of doing this, so someone saying they are “doing intermittent fasting” may actually be following a very different approach from someone else.
Time-Restricted Eating / Prolonged Nightly Fasting
Time-restricted eating focuses on when you eat rather than necessarily how much you eat.
Food and caloric drinks are consumed within a shortened daily eating window, typically ranging from around 4–12 hours, with the remaining hours spent without caloric intake.
A related term is prolonged nightly fasting, where calorie intake is reduced or eliminated overnight, creating an extended fasting period of more than 10 hours.
For many people, this can simply mean finishing dinner in the evening and not eating again until breakfast the following morning.
A 12–14-hour overnight period can be a relatively gentle approach for some healthy adults. There is growing interest in how periods without food influence metabolic health and cellular processes, including those involving mitochondrial function.
Longer isn’t automatically better.
Alternate-Day Fasting
Alternate-day fasting involves a cycle of:
A day of complete fasting → followed by a day of unrestricted eating → then repeated.
Some variations allow a small amount of food or calories on the fasting day rather than complete fasting.
This is considerably more restrictive than simply extending your overnight fasting period.
Intermittent Energy Restriction
Intermittent energy restriction involves alternating between days of very low calorie intake and days of normal calorie intake.
On low-calorie days, intake may be as little as 400–500 calories, depending on the specific protocol.
This is a significant restriction and isn’t something that should be undertaken casually. Individual nutritional requirements, health status and medications all need to be considered.
The 5:2 Diet
The 5:2 approach is a form of intermittent energy restriction.
It involves:
5 days: normal eating
2 days: significantly reduced calorie intake
On the two lower-calorie days, intake is generally limited to no more than around 25% of an individual’s usual daily energy requirements.
The two days can be consecutive or spread throughout the week, depending on the approach being followed.
Calorie Restriction
Calorie restriction is different from fasting because meal frequency is generally maintained.
Instead, total daily calorie intake is reduced over an extended period without intentionally causing malnutrition.
For example, someone might continue eating three meals a day but reduce the overall energy content of those meals.
This distinction is particularly useful when discussing weight loss. If fasting helps someone lose weight, it is generally because the eating pattern makes it easier to consume fewer calories overall.
Fasting-Mimicking Diet
A fasting-mimicking diet (FMD) is a periodic, multi-day eating programme designed to mimic some of the physiological effects of fasting while still providing a small amount of food.
A typical protocol lasts around five days and is very low in calories and relatively low in carbohydrates.
Unlike a true fast, you are still consuming food during the fasting-mimicking period.
These programmes are quite specific and shouldn’t be confused with simply following a healthy, lower-calorie diet.
Why are you fasting?
Before starting a fasting regime, consider what you’re hoping to achieve.
If you already maintain a well-balanced diet, consume relatively little ultra-processed food, drink enough water, move regularly and get adequate sleep, there may be little reason to introduce frequent or prolonged fasting.
Sometimes we become so focused on finding the next health intervention that we overlook the foundations.
Fasting for weight loss
Fasting can help some people lose weight, but it isn’t a special form of calorie burning.
Research suggests that intermittent fasting can be effective for weight loss, but overall energy restriction appears to be an important part of the picture. Recent reviews have generally found intermittent fasting to produce weight loss comparable to conventional calorie restriction when energy restriction is similar. (PubMed)
In practical terms, fasting may help because it reduces the number of eating opportunities and therefore makes it easier for someone to consume fewer calories overall.
If you’re comfortable eating three balanced meals a day, you don’t necessarily need to introduce fasting to lose weight.
For some people, improving meal quality, portion sizes, protein and fibre intake, movement, sleep and overall dietary habits may be a much more sustainable approach.
Fasting for “detoxification”
Fasting is often promoted as a way of “detoxing” the body.
But your body already has sophisticated systems for processing and eliminating unwanted substances, particularly through the liver, kidneys, gut, lungs and skin.
Rather than relying on prolonged fasting, it may be more helpful to focus on the foundations that support these systems:
- Eating plenty of vegetables, fruit and other plant foods
- Getting enough fibre
- Drinking adequate fluids
- Eating sufficient protein and micronutrients
- Limiting alcohol and highly processed foods
- Supporting regular bowel movements
- Getting adequate sleep and movement
Where nutritional deficiencies or specific needs have been identified, targeted supplementation may also be appropriate.
If your goal is to support your body’s natural detoxification processes, improving your diet may be more useful than simply eating less.
Fasting and the mitochondria
The mitochondria are often described as the “powerhouses” of our cells because they produce much of the energy our cells need.
Fasting has attracted considerable scientific interest because periods without food can influence cellular energy-sensing pathways and processes involved in cellular maintenance and mitochondrial function.
However, this doesn’t mean that you need to undertake prolonged fasts to “reset” or “optimise” your mitochondria.
Regular movement, adequate sleep, sufficient nutrients and a varied, plant-rich diet are also important for mitochondrial health.
A sensible overnight period without food may be one piece of the picture, it doesn’t need to become an extreme practice.
Fasting and blood sugar
This is an important consideration that is sometimes overlooked.
If you regularly experience energy dips, intense hunger, cravings, irritability, shakiness or difficulty concentrating when you haven’t eaten, extending your fasting window may not be the best place to start.
A diet high in sugary foods, refined carbohydrates and highly caffeinated drinks can also make it harder for some people to maintain stable energy and appetite.
Before experimenting with longer periods without food, it may be more appropriate to work on blood sugar balance first.
This can include building meals around:
- A good source of protein
- Fibre-rich vegetables and plant foods
- Healthy fats
- Slow-release or minimally processed carbohydrates
- Regular, balanced meals
Once these foundations are in place, some people may find that a gentle overnight fasting window feels comfortable and natural.
Others may simply feel better eating regularly.
There isn’t one approach that works for everyone.
What about metabolic health?
Research into intermittent fasting and time-restricted eating is continuing to grow. Studies have reported improvements in some measures of metabolic health, particularly in people with overweight or obesity, including weight, fasting insulin and HbA1c in some time-restricted eating interventions. However, results vary according to the fasting pattern, eating window, population and overall diet. (PubMed)
This is why it is difficult to say that one particular fasting window is universally “best”.
The quality of the food you eat, your overall energy intake, sleep, movement and individual metabolic health all matter too.
Do you need to fast every day?
Not necessarily.
If you’re already eating a nutrient-dense diet, consuming relatively little ultra-processed food, staying hydrated, moving regularly and getting enough sleep, there may be little reason to introduce frequent or prolonged fasting.
And if you find yourself thinking that a 12-hour fast is good, therefore 14 hours must be better, and 16 hours must be better still, remember:
Health doesn’t work quite that simply.
The longest fasting window isn’t necessarily the healthiest fasting window.
Who should be cautious with fasting?
Fasting isn’t suitable for everyone.
Extra care is needed if you:
- Have diabetes or problems with blood glucose regulation
- Take medication that can affect blood glucose
- Are underweight or struggling to maintain your weight
- Are pregnant or breastfeeding
- Have a history of an eating disorder or restrictive eating
- Are a child or adolescent
- Have a medical condition requiring regular food intake
- Are taking medications that need to be taken with food
If you have a medical condition or take medication, speak to your GP or appropriate healthcare professional before making significant changes to your eating pattern.
How to approach fasting gently
If fasting is appropriate for you, it doesn’t need to mean going without food for long periods.
A simple starting point for some people may be to establish a consistent 12–14-hour overnight period without food, for example finishing dinner at 7pm and eating breakfast between 7am and 9am.
You can then pay attention to how you feel.
Are your energy levels stable?
Are you sleeping well?
Are you genuinely hungry when you eat?
Are you able to concentrate?
Are your meals still nourishing and balanced?
And perhaps most importantly:
Does fasting make your life and your health better, or does it simply make eating more complicated?
When you do eat, focus on nourishing your body rather than compensating for the period without food. Break your fast with a balanced meal containing protein, fibre, healthy fats and nutrient-rich carbohydrates rather than immediately reaching for highly processed or sugary foods.
Fasting isn’t a competition
There can be a tendency to think that if a 12-hour fast is good, 14 hours must be better, and 16 hours must be better still.
But fasting is not a competition.
The goal isn’t to see how long you can go without eating.
The goal is to find an approach that supports your health, provides adequate nutrition and fits comfortably into your life.
For some people, a gentle overnight fast may fit beautifully into a healthy lifestyle. For others, regular balanced meals may be a better option.
Rather than asking:
“How long can I go without eating?”
Try asking:
“What am I hoping to achieve, and is fasting the best way to achieve it?”
Fasting can be a useful tool, but it is only one tool.
Building a nourishing diet, supporting blood sugar balance, moving regularly, sleeping well and giving your body the nutrients it needs will always be important foundations for health.
References
- Semnani-Azad, Z. et al. (2025). Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ, 389, e082007. (PubMed)
- Wu, X. et al. (2026). Comparison of Different Intermittent Fasting Patterns or Different Extents of Calorie Restriction for Weight Loss and Metabolic Improvement in Adults: A Systematic Review and Network Meta-Analysis of Randomized Controlled Trials. Nutrition Reviews, 84(3), 487–499. (PubMed)
- Hua, Z. et al. (2025). Intermittent fasting for weight management and metabolic health: An updated comprehensive umbrella review of health outcomes. Diabetes, Obesity and Metabolism, 27(2), 920–932. (PubMed)
- Welton, S. et al. (2020). Intermittent fasting and weight loss: Systematic review. Canadian Family Physician, 66(2), 117–125. (PubMed)
- Wei, X. et al. (2022). Intermittent Energy Restriction for Weight Loss: A Systematic Review of Cardiometabolic, Inflammatory and Appetite Outcomes. Biological Research for Nursing. (PubMed)
- Fernandes-Alves, D. et al. (2026). Systematic Review and Meta-analysis of Randomized Clinical Trials Comparing Time-Restricted Eating With and Without Caloric Restriction for Weight Loss. Nutrition Reviews, 84(3), 463–486. (PubMed)
Further reading
The evidence around fasting continues to develop, particularly around time-restricted eating, circadian rhythms, metabolic health and the longer-term sustainability of different approaches. For this reason, fasting should be viewed as an evolving area of nutritional research rather than a one-size-fits-all prescription.
Topics Included
- Fasting
- Intermittent fasting
- Time-restricted eating
- Prolonged nightly fasting
- Overnight fasting
- 14-hour fasting
- Alternate-day fasting
- 5:2 diet
- Calorie restriction
- Fasting-mimicking diets
- Fasting and weight loss
- Fasting and blood sugar
- Metabolic health
- Mitochondrial health
- Detoxification and nutrition
- Blood sugar balance
- Naturopathic nutritional therapy
- Healthy eating
- Nutritional therapy
Nutritional Therapy in Exeter.
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What is Nutritional Therapy?
Nutritional Therapy is a holistic approach to health and wellbeing that focuses on using food and nutrition to support the body's natural healing processes.
I provide personalised nutrition plans tailored to individual needs.
Whether you're looking to improve digestion, boost energy levels, manage weight, improve your nutrition intake, or address specific health concerns. Nutritional Therapy can offer valuable insights and support on your journey to optimal health.
My Nutritional Therapy diploma is held with the School of Health, and I am a registered Nutritional Therapist with the Federation of Nutritional Therapy Practitioners.
What is the difference between a; dietitian, nutritionist and nutritional therapist.
Dietitian's - Dietitian's provide practical guidance to sick individuals to help them make appropriate, healthy choices for a specific medical conditions. They often work as part of a clinical team, including for example doctors, nurses, physiotherapists etc. They take a direct approach to the illness being presented to them, not the body as a whole.
Nutritionists - Registered nutritionists are qualified to provide information and nutrition advice about food and eating habits. They may take a similar approach to a Nutritional Therapist. Nutritionists normally operate out of private practices. Dieticians will normally operate out of the NHS.
In general, nutritionists provide evidence-based information and guidance about the impacts of food and nutrition on the health and wellbeing of humans
Nutritional Therapists
Nutritional therapists practice complementary medicine, taking a holistic approach to the symptoms that are presenting in the body, They provide recommendations for diet and lifestyle to reduce or prevent health issues and illnesses. They work on the belief that the body has underlying nutritional and biochemical imbalances that lead to poor health, including mental health problems.
