Is skipping meals bad for you... or could intermittent fasting actually be the key to burning fat?
Skipping breakfast used to be considered a diet sin, but now missing entire meals could contribute to weight loss. Intermittent fasting is growing in popularity, yet it wasn’t always a choice for our ancestors.
Our hunter-gatherer predecessors had to hunt and forage for food, leading to long periods when eating wasn’t an option. Is this behaviour ingrained in our evolution, and could tapping into it be the key to a healthier lifestyle?
So what exactly is intermittent fasting? Fasting has been practised for thousands of years, both out of necessity and for cultural, religious, and health reasons.
In simple terms, intermittent fasting is an eating pattern where you cycle between periods of eating and fasting. For example, with the 16/8 method, you eat only between 11am and 7pm and fast for the remaining 16 hours, giving you an 8-hour eating window.
Unlike traditional diets, intermittent fasting focuses on when you should eat rather than what to eat. Of course, a balanced, healthy diet is important, but this method is less restrictive than other diets.
As with any diet or lifestyle change, you should consult your GP to ensure there is no risk to your health.
How intermittent fasting helps with weight loss
When you eat regularly throughout the day, your body uses the calories from food for energy. The more consistently you provide fuel, the less likely your body is to tap into your fat stores.
However, when you’re following an intermittent fasting diet, once your body has used up the calories from your last meal, it starts to use your fat stores for energy.
Sandra Cohen, Nutritional Therapist from Doctify, explains: “Fasting triggers a metabolic shift in which the body transitions from using glucose as its primary fuel source to burning stored fat for energy.
“This process, known as ketosis, enhances mitochondrial function and cellular repair through autophagy, where the body clears out damaged cells and regenerates new, healthier ones.”
Sandra adds: “For weight loss, I recommend intermittent fasting with a minimum fasting window of 12 hours, as this allows the body to shift into fat-burning mode while supporting metabolic health.
“Depending on individual factors such as blood sugar regulation, overall health status, and genetics, some people may benefit from extending the fasting period to 14-16 hours to enhance fat oxidation and improve insulin sensitivity.”
What are the benefits of intermittent fasting?
Intermittent fasting can have lots of potential benefits – and some of them might surprise you! According to Hopkins Medicine, intermittent fasting can support weight loss (and in turn help with type 2 diabetes), sharpen your memory, and improve your heart and tissue health.
Sandra Cohen outlines the potential benefits:
- Metabolic health – enhances insulin sensitivity, lowers blood sugar, and reduces the risk of type 2 diabetes.
- Cognitive benefits – supports brain health by increasing BDNF (brain-derived neurotrophic factor), which may reduce the risk of neurodegenerative diseases.
- Weight loss and fat burning – promotes fat oxidation and reduces inflammation.
- Longevity and cellular repair – induces autophagy, which removes damaged cells and may slow ageing.
- Gut health – allows the digestive system to rest, reducing bloating and improving gut microbiome diversity.
Popular intermittent fasting methods for weight loss
16/8 method
The most popular method of intermittent fasting is 16/8 – fasting for 16 hours and having an 8-hour window in which to eat. During your fast, you can drink water, unsweetened black or herbal tea and black coffee.
The first thing to do is choose your 8-hour window of time in which you will be eating. You’ll need to consider your lifestyle, for most people eating between 11am-7pm or 12pm-8pm fits their schedule. However you can choose any 8-hour window that suits you, you might prefer eating earlier in the morning, or late at night.
Here are some popular schedules for eating times:
- 10am-6pm – Good for those who enjoy breakfast but don’t eat late
- 12pm-8pm – Skip breakfast and enjoy lunch and dinner
- 4pm-12am – Good for night owls, and those wanting to eat later
When you start fasting a great tip from Doctor O'Donovan in the video below, is to set an alarm for the start and end of your fast, so that you can keep track easily.
14/10 method
With any lifestyle change, starting small can be beneficial. If you’re new to fasting, the 14/10 intermittent fasting method is a more manageable approach. This involves fasting for 14 hours and having a 10-hour eating window, making it an easier way to ease into intermittent fasting.
- 8am-6pm – Ideal for those who want breakfast and lunch, skipping dinner
- 10am-8pm – Those who prefer breakfast and an early dinner
- 12pm-10pm – Skip breakfast and eat lunch and dinner later
The 14/10 and 16/8 methods are considered the most sustainable forms of intermittent fasting and can be maintained long-term if they work for you. The methods below are more intense and may not suit everyone, so it’s important to approach them with caution and consult a doctor before making any significant changes to your diet.
5:2 method
The 5:2 method involves eating normally for 5 days and following a low-calorie diet for 2 days, with an intake of around 500–600 calories (or one meal) on fasting days. For example, you could fast on Monday and Thursday, as the fasting days should not be consecutive.
This method is more challenging than the 16/10 method since it requires a drastic calorie reduction on fasting days and long periods without eating, which can be tough for beginners. However, once your body adjusts to the routine it should get easier.
Like other fasting methods, it’s important to stick to a healthy, balanced diet, even on fasting days.
Eat-Stop-Eat method
This approach is similar to the 5:2 method, but you don't eat anything on your two fasting days.
If you're considering it, starting with the 5:2 approach is a good idea, as it’s more manageable. If that works for you, gradually transitioning to full fasting could be a viable option, especially if you're focused on weight loss.
The concept behind this practice originates from Brad Pilon in his book, Eat Stop Eat, where he explains how it can aid in weight loss.
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With this method (and all others) it is really important to stay hydrated, especially during your fast days.
Fast Mimicking Diet (FMD)
This fasting method is a modified version where you consume very low calories (around 500-800) for several days in a row.
It’s meant to mimic traditional fasting without completely restricting food, which could be potentially easier for some people.
According to UCLA Health: “The FMD is primarily plant-based and designed to produce fasting-like effects in the body by targeting blood glucose, ketone levels, and other biological markers.”
There have been some studies that indicate that an FMD diet can help lower BMI and reduce overall body fat.
Alternate-Day fasting
With alternate-day fasting, you eat normally one day and fast the next, either eating nothing or very little on fasting days. Due to the extended fasting periods, this approach can be challenging to sustain over time and may not suit everyone.
One clinical study revealed that when testing a group of people over six months using alternate-day fasting vs. daily calorie restriction, there was no significant difference between the two groups in terms of weight loss at the end of the trial.
So this method can be very hard going, and may not yield better results than simply calorie restricting your diet daily. However, you may still reap other benefits on your body for having fasting periods.
One-Meal-a-Day (OMAD) method
OMAD is at the extreme end of intermittent fasting and is only suited to certain individuals, particularly those already comfortable with longer fasting periods.
This method involves eating just one meal per day within a 1-2 hour window, meaning you spend the remaining 22-23 hours fasting.
Because of the prolonged fasting period, it can lead to rapid weight loss, but it is generally unsustainable. It may also cause negative side effects such as dizziness, headaches, weakness, and nausea.
Additionally, the extended fasting period can increase the likelihood of poor food choices or binge eating when your fast breaks, as the body craves quick energy.
There is limited scientific research specifically on OMAD, so its benefits are not well-established. That said, you may still experience the general benefits of fasting with this method, but a less extreme approach could offer similar results more sustainably.
Warrior method
The warrior diet is similar to OMAD. It involves fasting for 20 hours and then having a 4-hour window in which to eat a big meal. This method allows for small amounts of food, such as fruit, vegetables, and protein during fasting.
Like OMAD there is little to no scientific research backing this method, and may even encourage overeating or binging during the eating window.
It is not a method that one should take lightly, but is slightly less extreme than OMAD since you can eat small amounts during fasting.
Spontaneous Fasting
Spontaneous fasting means skipping meals when you’re not hungry, without following a strict schedule, making it a flexible option.
However, there is limited research on this method, and it may not be the most effective approach. Skipping a meal can leave you feeling hungry later, increasing the likelihood of snacking.
The lack of structure may also lead to poor food choices, whereas a more structured approach allows for balanced meal planning, helping to prevent unhealthy grazing.
What to eat during a fast
Like any other diet – you need to eat a healthy balanced mixture of foods for it to help you lose or maintain your weight. Dr O'Donovan explains the importance of eating whole and nutrient-rich foods in a balanced meal. This includes:
- Fruits – Apples, oranges, bananas, berries, pears, tomatoes
- Vegetables – Leafy greens, broccoli, brussels sprouts, cauliflower, cucumber
- Wholegrains – Barely, buckwheat, quinoa, rice, oats
- Healthy fats – olive oil, avocado
- Protein – eggs, fish, meat, poultry, nuts, seeds
You should also avoid over-processed foods, white bread, white pasta, sugary drinks and anything else that will spike your blood sugar levels.
While fasting it is of the utmost importance that you keep hydrated, the best thing to do this is water. Most fasting types also allow for herbal tea, and black tea or coffee.
Exercise while intermittent fasting
Exercise can be done while you’re fasting, but there are a few things to consider. Sandra Cohen, Nutritional Therapist from Doctify advises: “Low-intensity workouts (walking, yoga) are generally well-tolerated. Strength training or high-intensity exercise may be better post-fasting when energy levels are restored.”
Exercising during a fast can have negative effects like fatigue and dizziness. You may also find it difficult to exercise at these times due to lack of food, so performance can be poorer and less effective.
Who should not do intermittent fasting?
Intermittent fasting isn’t suitable for everyone, most research that has been done is on healthy adults, and there is still research needed for the long-term effects.
Bupa advises you should not take part in intermittent fasting:
- if you are pregnant
- have type 1 diabetes
- have a history of disordered eating
- have anxiety or depression
If you have any concerns it’s always best to check with your doctor before making any diet or lifestyle changes.
Intermittent fasting for women
There’s been less research into the effects of intermittent fasting on women’s bodies. There will be times when fasting is not recommended.
Sandra Cohen, Nutritional Therapist from Doctify, says: “Women’s hormones are particularly sensitive to caloric restriction and fasting duration.
“During perimenopause and menopause, oestrogen and progesterone levels fluctuate, and excessive fasting can amplify cortisol (stress hormone) production, leading to increased insulin resistance, thyroid dysfunction, and disruptions in sex hormones.
“For women already dealing with high-stress levels, adrenal dysfunction, or HPA axis dysregulation, prolonged fasting can further deplete energy reserves, increasing symptoms like fatigue, mood swings, weight gain, and sleep disturbances.”
Sandra goes on to explain that women may benefit from shorter fasting windows. They also need to be very diligent in eating nutritious, protein-rich meals during eating windows to prevent stress on the body.
As with every type of fasting, always consult a doctor before making changes. When you have done so, always start small and build gradually up if you feel it suits you.
Intermittent fasting and type 2 diabetes
There has been some research into whether intermittent fasting can help type 2 diabetes. Diabetes UK says: “People have put their type 2 diabetes into remission following an intermittent fasting diet. But we need more research before we can say that fasting diets can help you go into remission long-term.”
The key benefit of intermittent fasting is its potential to aid in weight loss, which can, in turn, help improve type 2 diabetes.
If you have type 2 diabetes and are considering intermittent fasting, it is crucial to consult your doctor or healthcare provider before making any changes to your routine.
Diabetes UK tells us: “Intermittent fasting changes what you eat and when. You may be reducing the amount of carbohydrates you eat and this can have a big impact on your blood sugar levels.”
Common mistakes that slow weight loss
The good news is that intermittent fasting can help with weight loss but that doesn’t come without small print.
One common issue people face with fasting is the tendency to binge during their eating window. If weight loss is your goal, it’s important to eat a healthy, balanced diet during your eating hours and avoid overeating.
It can also be helpful to plan your meals and track your calorie intake using an app or a notepad. This can help you stay more mindful of your choices and stay on track.
Is intermittent fasting the right diet for you?
When done correctly, intermittent fasting can be beneficial for weight loss, but the evidence isn’t strong enough to prove it’s better than simply following a calorie-restricted daily diet combined with regular exercise.
When starting a fasting plan, it's important to start small, testing how your body responds. If the results are positive, you can continue. It's worth noting that hunger cravings may be intense at first, but as your body adjusts, fasting can become more manageable.
Intermittent fasting can be particularly helpful if you struggle with late-night snacking or tend to graze throughout the day, as it provides structure and helps you develop better eating habits.
It’s essential to maintain a healthy, balanced diet during fasting and stay hydrated. There are many other potential benefits to fasting beyond just weight loss, so if you're curious, it could be worth giving it a try!
Changing tastes as you age
As well as making healthy choices, did you know that we should be altering our diet as well as our exercise regime as we get older too? Find out how to eat well and get the right exercise at any age.
