I’m a nutritionist – here’s the REAL secrets of successful intermittent fasting (and who should avoid it completely)

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Written By Rivera Claudia

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Intermittent fasting has become one of the most popular diets in recent years.

Followers of the eating plan – who drastically cut calories for a day or two each week, or consume all their food during a brief window of time each day – say that it helps with weight loss, it reduces the risk of type 2 diabetes and boosts their gut microbiome.

And big names including Rishi Sunak, Jennifer Aniston and Hugh Jackman swear by fasting to keep their health and weight on track.

‘Some of the strongest research for fasting is around the potential to reduce insulin resistance and lower the risk of type 2 diabetes,’ says Rob Hobson, registered nutritionist at Healthspan and author of Unprocess Your Life.

‘Other potential benefits include reducing oxidative stress and inflammation in the body, which both increase ageing and disease risk; lowering cholesterol and blood pressure and protecting brain health.’

Intermittent fasting is said to help with weight loss , reduce the risk of type 2 diabetes and boosts gut microbiome

Yet recent research presented at a US conference suggested intermittent fasting isn’t the silver bullet many adherents believe it to be. 

A study of over 20,000 adults by researchers at Shanghai Jiao Tong in China found that people who eat within a window of eight hours a day or less may double their risk of death from heart and vascular disease, compared with those who maintain a more typical eating window of 12 to 16 hours.

But Mr Hobson explains: ‘This study has not undergone peer review or been published in its entirety, and its findings are based on participants’ reported eating habits over just two days.’

He also notes that many of the participants may have had pre-existing heart problems.

However, while inconclusive, the research is a reminder that intermittent fasting isn’t always a fast-track to weight-loss.

‘You can’t just eat what you want with intermittent fasting if you want to lose weight. You have to eat balanced meals during the feeding period,’ says Mr Hobson.

So how can you get all the benefits of fasting without the downsides, and who should avoid intermittent fasting altogether?

Here, Mr Hobson reveals everything you need to know and his expert tips for getting the most out of your IF plan…

Big names including Rishi Sunak , Jennifer Aniston and Hugh Jackman swear by fasting to keep their health and weight on track

Big names including Rishi Sunak , Jennifer Aniston and Hugh Jackman swear by fasting to keep their health and weight on track

It can reduce your appetite

You might expect fasting to make you feel ravenous, but it’s been shown to impact the hormones that help to regulate appetite.

Fasting initially increases the levels of the hunger hormone ghrelin but over time, and with regular fasting, levels can adjust.

This potentially leads to reduced hunger levels overall.

Fasting can help to improve sensitivity to leptin, the ‘fullness’ hormone, so you maintain satiety for longer, which may help with weight maintenance.


Rob Hobson, sports and registered nutritionist, explains the different types of fasting. 

  • 16/8 method: Fast for 16 hours each day and eat during an eight-hour window, for instance between 8am and 4pm or 10am to 6pm. 
  • 5:2 method: Created by Michael Mosely, followers eat normally for five days of the week and reduce calorie intake to about 500 to 600 calories for two non-consecutive days.
  • Time-restricted eating (TRE): This is similar to the 16/8 method but it can vary in window lengths; for example, 14 hours of fasting and 10 hours of eating, or 20 hours fasting and four hours of eating. The safety and sustainability depend on the length of the eating window and ensuring nutritional needs are met. 
  • 24-hour fasts: This involves going 24 hours without eating (known as a full-day fast) once or twice a week. While many can safely manage 24-hour fasts, they can be more challenging and may not be suitable for everyone.
  • Extended fasts: Fasting for more than 24 hours, up to 48 or 72 hours, should be done under medical supervision, especially for longer durations, due to increased risks of nutrient deficiencies, electrolyte imbalances and other health issues. Rishi Sunak fasts for 36 hours, from Sunday night to Tuesday morning every week.


Eat the RIGHT calories on fast days

If you’re following the 5:2 diet, the fasting days can be tricky to maintain, especially if you are not sure what to cook within the 600 or 800 calorie per day limit.

It’s important to remember that not all calories are created equal – and obtaining energy from unhealthy sources such as quickly digested carbohydrates such as UPFs, white bread and sweat treats, will just increase hunger and cause blood sugar imbalances.

Instead, plan your fast day snacks – and meals on your ‘normal’ days – around protein, fibre and healthy fats to keep you feeling full between meals.

This will also ensure that you get an adequate intake of micronutrients that are essential to good health.

A multivitamin, such as Healthspan’s MultiVitality Pro, could also help make sure you’re getting all the nutrients you need.

You might get ‘fanger’ (that’s fasting-induced anger!)

You may be familiar with ‘hanger’, the grumpiness that can set in when you’re feeling hungry – and initially, the increased hunger from fasting can cause the same irritability.

Fluctuations in blood sugar levels can also influence mood and low blood sugar can lead to irritability and mood swings.

Fasting also triggers the stress response leading to increased cortisol so during long fasting periods this may lead to increased feelings of anxiety in some people.

The good news is that your body will adapt to fasting so over time these side effects can subside.

You won’t be able to exercise at your usual pace

If you are new to fasting, then pace your training sessions.

This is particularly relevant to intermittent day fasting or calorie restriction, where energy levels are drastically reduced on fasting days.

Start with low intensity and increase slowly to the point you feel comfortable. This will help to reduce the risk of injury.

If you feel dizzy, lightheaded or weak at any point, then listen to your body and stop exercising.

Ask yourself if you need to break your fast or even adopt another fasting method?

Fasting is not suitable for children and pregnant women. Some women might find fasting more challenging or less beneficial during the second half of their cycle, called the luteal phase

Fasting is not suitable for children and pregnant women. Some women might find fasting more challenging or less beneficial during the second half of their cycle, called the luteal phase

You’ll need to drink more than you think

Food contributes to hydration levels in your body so you’ll have to compensate on your fasting days with more liquid than usual.

It’s even more vital to remain well-hydrated during your training sessions and if your workouts are intense, and you tend to sweat a lot, add electrolytes to your water to help replenish lost minerals.

Strength training is best at the end of your fast period…



Fasting may contribute to improved heart health by affecting various factors such as blood pressure, cholesterol levels, triglycerides, and inflammatory markers, all of which are risk factors for heart disease.


Fasting has been linked to a lower risk of neurodegenerative diseases and can promote brain health. It may enhance brain function, encourage the growth of new neurons, and protect against brain damage due to its effects on BDNF (brain-derived neurotrophic factor) levels and through the reduction of oxidative stress and inflammation.


Some animal studies suggest that fasting can increase lifespan, although more research is needed in humans to understand the effects fully.


Fasting can reduce markers of inflammation, which is a key driver of many chronic conditions.


By giving the digestive system a break, fasting may help in the healing of various digestive system disorders. It can also improve gut health by impacting the microbiome, though more research is needed in this area.


If your session is strength and power based, then being able to feed your body for recovery afterwards is essential.

The trick is to time your workout towards the end of your fasting window, so if you’re following the 16:8 and eating between 8am and 4pm, finish your weights session before 8am.

Then make sure you’re eating enough protein (about 20-25g) after exercising so you can help your body make more muscle.

Do your cardio at the start of your fast

If you’re doing a cardio-based workout (running, cycling, swimming or aerobics), try scheduling it for immediately after your eating window.

So, for those following the 16:8, finishing at 4pm, it will be from late afternoon onwards.

You can also plan your last meal around carbohydrates to ensure muscle glycogen stores, which are the body’s source of energy, are packed to fuel your workout.

But is intermittent fasting right for YOU?

Fasting is not suitable for children and young teens as they’re at a stage of life when the body is still developing, especially bones.

It may seem logical for overweight children and teens to lose weight by fasting, but this may result in nutrient insufficiencies and doesn’t help them to develop healthy eating behaviours.

It’s also not recommended fasting for anyone with increased nutritional needs such as during pregnancy or when recovering from illness.

Long-term fasting may impact on nutrient intake and even more so if someone is also cutting out food groups as well.

While there’s no universally ‘bad’ time to fast, some women might find fasting more challenging or less beneficial during the second half of their cycle, called the luteal phase.

During this phase – between ovulation and the start of menstruation – some women experience increased hunger and cravings due to higher energy demands.

Progesterone levels are elevated, which can increase metabolism slightly and lead to a higher caloric need.

Fasting can also exacerbate PMS symptoms such as mood swings, fatigue and discomfort, making it a less ideal time to restrict food intake.


For sociable types: 6:1

Similar to the 5:2 pattern, in the 6:1 there is only one day of reducing calories rather than two. It can work best for people who work hard and play hard and need to maintain energy levels.

‘The last thing you want to do is leave the office for drinks on an empty stomach, which is always a recipe for disaster,’ says Rob Hobson. ‘Fasting can also interfere with dining out.

‘The best type of fasting may be ‘eat-stop-eat’, in which you have a complete fast for 24 hours, during a quiet weekend every one or two weeks.

For parents on the school run: 16:8

Busy mornings can often mean skipping breakfast as you dash around getting the kids ready for school.

Before you know it, it’s mid-morning and you’re ready to eat. You like to sit down as a family to eat with the children so your evening meal is served early.

‘Without realising it you are already conforming to the 16:8 method of fasting – only consuming food within an eight-hour window,’ says Hobson.

For ambitious types: 16:8

‘Busy work-focused individuals require a steady source of micronutrients and energy to deal with the demands of their hectic schedules,’ Hobson says.

‘A lack of food can make it difficult to concentrate and there may also be an increased demand for nutrients such as the B vitamins as the body copes with excess stress levels.

‘Eating within an eight-hour window leaves plenty of time throughout the day to nourish the body.’

For retirees: 5:2

Older people may find it easier to follow methods such as the 5:2.

Appetites diminish as you age so fasting days may feel like less of a burden and older people become slightly less active.

Being at home gives more scope to prepare nourishing, low calorie meals that may be more difficult for working people that buy lunch on the high street.

For gym-goers: 16:8

You need fuel to train and full days of fasting or days of very low calories can leave your muscles depleted of glycogen, which is required to give you the energy you need to get through workouts.

The 16:8 method means you can replenish your muscles with glycogen the night before ready for your training session in the morning.

If you eat at 7pm you will be ready for breakfast at 11am and if you time your training right then you will be able to get your post workout protein meal in shortly afterwards.


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