Intermittent fasting 101

Intermittent fasting has gained incredible popularity over the past few years, particularly when it comes to losing weight and fat. There have been numerous studies conducted looking at the effects of intermittent fasting on the body, and the potential benefits it can bring. But what exactly is intermittent fasting? Is it safe? And should you consider it? Evergreen Life takes an in-depth look.

What is intermittent fasting?

Whilst most diets focus on what to eat, intermittent fasting focuses on when you should eat. Intermittent fasting involves only eating at certain times of the day; it cycles between periods of fasting and eating. Because of this, intermittent fasting could be more accurately described as an eating pattern rather than a diet. Fasting can also be done for religious or spiritual reasons, including being practised in Islam, Christianity, Judaism and Buddhism.

How to do intermittent fasting

There are several ways to do intermittent fasting. There are differences between them, but they all follow the pattern of splitting your days or week into fasting and eating. During the fasting periods, you’ll always eat nothing or very little.

Here are three of the most popular methods of intermittent fasting:

The 16/8 method

The 16/8 method is a form of time-restricted eating (TRE) that involves consuming food within the specific window of eight hours each day – such as between 1pm and 9pm – and then fasting for the remaining 16 hours of the day.

The 5:2 diet

The 5:2 diet was made famous by doctor and journalist Michael Mosley, in his book ‘The Fast Diet’, published in 2013. In this method, it’s recommended that you eat as normal for five days of the week, and then restrict your intake on the remaining two days to approximately 20-25% of your usual calorie total – around 500 calories for women and 600 for men.

Alternate day fasting

With this method, you choose one or two non-consecutive days each week where you will fast for a full 24 hours. For the remaining days, you’re able to eat freely, so you only need to restrict your eating for half the time. It is important that you stay hydrated throughout any fasting period, but especially when you go a full day without food.

However, as with any fasting method, you should still make sensible choices and avoid overeating on unhealthy foods.

The potential impact of intermittent fasting

• Autophagy – Autophagy is how the body cleans out damaged cells so it can regenerate new, healthy ones. Fasting is thought to be an effective way to trigger autophagy. During calorie restriction, cells can initiate repair processes such as autophagy, where cells digest and remove older proteins that have built up inside cells.
• Weight loss – The main benefit – and ultimately why a lot of people choose to partake in intermittent fasting – an approach that does seem to promote weight loss, but studies to date have been small and of short duration. Supporting research includes an evaluation of 27 studies, all of which indicate that intermittent fasting helped participants to lose up to 13% of their body weight. However, these studies were of short duration – two to 26 weeks with two being of 1-year duration – so we’re currently unable to see the sustained impact, and longer-term research is needed to understand if intermittent fasting can play a sustainable role in weight loss. Also, the results produced from intermittent fasting aren’t actually that different from that of a continuous low-calorie diet – when carried out effectively. Although intermittent fasting does limit what you can eat – and when – individuals still have the option to steer clear of healthy foods, consuming high-calorie foods if they desire. This, in turn, could actually have the adverse effect, leading intermittent fasters to gain weight instead.
• Improved memory retention – Research by Dr Thuret from King’s IoPPN has shown that calorie-restricted diets can improve memory function, enhance learning processes in mice and human cells in vitro. A separate study conducted in rats suggested intermittant fasting could induce expression of the brain hormone BDN – which is responsible for encouraging the growth of new nerve cells. Although this form of “metabolic” therapy does seem to have positive effects on animals, findings that suggest the same for humans is limited. With this in mind, it’s impossible to say at this point whether there’s a positive correlation between intermittent fasting and enhanced brain function. Evolving research suggests that intermittent fasting has many benefits for cognitive function but larger studies are needed. However, more research is needed before determining whether it could be regarded as having a genuine impact.
• Possible reduced anxiety and depression – Research demonstrates that fasting interventions may have a positive impact on anxiety and depression.
• Possible reduced insulin resistance – A study by the University of Alabama involving a small group of obese men with prediabetes found that those who partook in intermittent fasting had lower insulin levels and significantly improved insulin sensitivity suggesting that intermittent fasting may possibly help to prevent type 2 diabetes. However, there’s contradictory research out there too, suggesting that intermittent fasting’s ability to lower the risk of diabetes isn’t as effective for women as it is for men. Research conducted in 2005 found that their blood sugar levels actually worsened after a period of intermittent fasting – suggesting that this perceived correlation isn’t as widespread as people may first think. It’s also important to note that on each fasting day, subjects were informed that they could eat whatever they wished and that double their usual intake would be required to maintain body weight.
• Possible reduced inflammation – A study on the blood of 12 men has shown that intermittent fasting can influence some inflammatory processes. Chronic inflammation has been associated with heart disease, cancer, diabetes, bowel diseases, and arthritis.
• Possible cancer preventative – It’s possible that intermittent fasting might also decrease the risk of cancer, or slow cancer growth, as revealed in recent studies. As well as encouraging weight loss – with obesity being a significant risk factor for certain cancers – one particular study revealed that a fasting-mimicking diet, when paired with chemotherapy, slowed the progression of both breast cancer and skin cancer. When combined, these two treatment methods caused the body to produce a higher number of common lymphoid progenitor cells and lymphocytes – both of which are beneficial for fighting cancer. The suggestion that intermittent fasting could help prevent cancer is also displayed through a study with rats, which is yet to be fully explored or conducted amongst humans. Despite the potential effect, it’s essential that cancer patients consult their health practitioner before fasting, as it may not be safe for individuals who are malnourished, for those who suffer with chronic diseases, or for those suffering from cancer cachexia (weakness and wasting of the body due to severe chronic illness). 

The risks of intermittent fasting

As with any diet or eating method, there are benefits and possible risks to consider. Intermittent fasting will not be suitable for everyone. Those who have a history of eating disorders should avoid intermittent fasting, and those with underlying health conditions should consult a medical professional before undertaking a diet of any kind.

Fasting for long periods – such as 24, 36, 48 and 72 hours – could actually be dangerous for you and could cause your body to store fat instead of burning it.

The following is a list of instances where intermittent fasting shouldn’t be attempted, unless with the close management of a doctor:

• Any long-term medical condition
• If you’re pregnant
• If you’re breastfeeding

Possible side effects of intermittent fasting

We’ve already covered some of the benefits of following the intermittent fasting method, now let’s explore the possible negative side effects:

• Hunger – You’re probably not surprised by this one, but hunger and food cravings are common side effects of intermittent fasting. One study involved 112 participants, who were randomised to either try intermittent fasting or continuous energy restriction. Those who took part in intermittent fasting reported higher hunger scores than those who continuously restricted their caloric intake.
• Overeating – According to Harvard Medical School, some people could experience the urge to overeat due to the brain’s hunger centre and appetite hormones being sent into overdrive by periods of fasting. Dr. Frank Hu, chair of the department of nutrition at the Harvard T.H. Chan School of Public Health, says, “it’s human nature for people to want to reward themselves after doing very hard work, such as exercise or fasting for a long period of time, so there is a danger of indulging in unhealthy dietary habits on non-fasting days.”
• Mood changes – Is ‘hanger’ a real thing? Research has shown that low blood sugar levels could cause you to feel irritable, which could explain why some people experience mood disturbances when they fast. Another study also found increased anxiety and irritability along with poorer concentration when examining short-term fasting in women.
• Headaches – Headaches have been cited as a common side effect of intermittent fasting, and they’ve been found to occur within the first few days of starting a new fasting method. Research has suggested that caffeine withdrawal and low blood sugar levels during fasting days could contribute to these headaches.

Participants in a 2019 observational study reported the following mild side effects from fasting:

• Sleep disturbances
• Fatigue
• Headaches
• Dry mouth
• Muscle pain
• Abdominal bloating
• Diarrhoea
• Cravings
• Nausea

What can you eat during intermittent fasting?

Although you can eat ‘as normal’ on your chosen days or hours of non-fasting – depending on which method you choose to follow – it’s important that you don’t overindulge in too much food, particularly those that are high in calories and low in nutrition.

Harvard Medical School suggests that you avoid refined grains and sugars, and instead, eat plenty of healthy foods, such as:

• Fruits
• Vegetables
• Beans
• Lentils
• Whole grains, such as brown rice, quinoa, oats, and barley
• Lean proteins, such as poultry, fish, beans, lentils, tofu, nuts, seeds, cottage cheese, and eggs
• Healthy fats, such as fatty fish, olives, olive oil, coconuts, avocados, nuts, and seeds

Quick tips for intermittent fasting

Stay hydrated

Several side effects of intermittent fasting – such as headaches and fatigue – can often be caused by dehydration. Be sure to drink plenty of water, especially during your fasting days. You can also drink non-caloric drinks on these days, such herbal teas.

Eat slowly and carefully

Resist the urge to binge during your eating periods. Eat frequent meals slowly – every three hours if you can – to ensure you’re getting enough calories in. Although you’re fasting, it’s still important that you eat the correct amount.

Plan in advance

Once your fasting time is over, plan out your healthy meals in advance, so you can be sure they contain enough protein and vegetables.

Prioritise sleep

We’ve already discussed how intermittent fasting can cause sleep disturbances but getting too little shut-eye could make it more difficult to keep your new diet changes on track. Sleep plays an important role in regulating hormone levels, including leptin and ghrelin, also known as the ‘hunger hormones’. A lack of sleep has been found to cause increased levels of ghrelin and decreased levels of leptin, which can lead to increased appetite and hunger. So always prioritise getting those seven-nine hours of sleep if you’re aged 18-64, or seven-eight hours of high-quality sleep if you’re aged over 65 if you can. In fact, some studies indicate that 7 hours could be the optimum amount of sleep time for those who are middle aged and older. Look out for the Sleep Quality Check in the Happiness section of the Evergreen Life app, which can help you slumber more seamlessly.

Eat the best way for you

Hopefully, you now feel a little more educated about intermittent fasting. As with any diet or eating method, it’s always important to prioritise good nutrition – with plenty of colourful fruits and vegetables, the right kind of carbohydrates, lean protein, and healthy fats.

Intermittent fasting may have health benefits, but we can’t be sure about many of them until further studies have been conducted, and there are also risks associated. Be sure to speak to a qualified nutritionist or your GP before embarking on any kind of fasting method.

Before you embark on a new way of eating, what score would you give your current food and nutrition? Could you improve it? Be as well as you can be, starting from the inside. Download the Evergreen Life app today, and get started straight away on your wellness journey.

Reviewed by:

Dr Brian Fisher MBBch MBE MSc FRSA – Clinical Director

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