Everything You Need To Know About Intermittent Fasting

Everything You Need To Know About Intermittent Fasting

Intermittent fasting might be on the rise, but is it right for you? Skipping meals seems like an obvious way to lose weight, but there is more to this diet trend than first impressions. We asked a couple of leading nutritional therapists to explain how it works and what you can hope to achieve.
Photography: iSTOCK/TANYAJOY

In a nutshell, what is intermittent fasting (IF)?

“IF is not a diet; it’s a lifestyle. Think of it as a timed approach and pattern of eating that cycles between brief periods of restricting or eliminating food for a specific period of time or not eating for longer periods of time (up to 36 hours). Although IF has actually been practised for centuries, it’s seen a revival in recent years as a practice that promotes health, particularly in relation to healthy ageing.” – Catherine Sharman, nutritional therapist & founder, Après Food Co

What is it designed to achieve?

“Research suggests IF could benefit human health in a variety of ways, including weight loss. Studies on humans have shown weight-loss results but subjects also reported experiencing better sleep, more energy in the mornings and less hunger at bedtime. Studies have also found that IF can lower markers of inflammation and improve insulin sensitivity and lower insulin levels, which makes stored body fat more accessible.” – Karen Preece Smith, nutritional therapist, KPS Nutrition
“Typically, the reason people do IF is for weight loss. However, there are other improvements to markers of our health, associated with chronic health issues such as blood pressure and cholesterol levels that are the underlying reason for following IF as a lifestyle.”  – Catherine 

How does it work?

“All the methods are based on the same principle: as energy intake is reduced during fasting periods, the body will use stored fat for energy and become more metabolically flexible. In short, time-restricted eating gives your body more time to use up fat. When we eat, our body uses carbohydrates for energy, and if we don’t need them right away, they get stored in the liver as glycogen or converted into fat. After you’ve finished eating for the day, your body continues to run on glucose from the carbohydrates that you’ve just eaten for a few hours before tapping into stored carbohydrates (glycogen) in the liver. That glycogen lasts for several hours before running out roughly eight to 12 hours after we’ve stopped eating, which is when our body begins to tap into its stored fat. When you shorten your eating window and extend your fasting window, you spend longer in this fat-burning mode of your metabolism, thus potentially losing weight.” – Karen
“IF may additionally be of benefit to the gut microbiome. The cycles of fasting and feeding rhythms possibly help to diversify our gut microbial community, which in turn affects body metabolism. The extended period of fasting may also lead to a reduction in gut permeability, which as a result leads to reduced postprandial endotoxemia and has a positive effect on our gut-brain link.” – Catherine

Why has it become popular recently?

“Dr Michael Mosley and others have been promoting it for weight loss and benefits such as cognitive clarity and energy.” – Karen
“If you sustain a ‘traditional’ very low-calorie diet for a long period of time, the body is likely to adapt and prevent further weight loss. This, together with the compliance that’s needed for this way of eating, may result in disordered eating, including binge eating, just in order to cope psychologically. This can lead to ‘yo-yo’ dieting and fluctuations of weight gain versus weight loss. IF ensures the calorie restriction is for brief and sustainable periods of time, which may prevent the adaptations associated with traditional dieting. IF will still require a level of discipline and understanding, and the research does not consistently show it is superior, but it could feel more achievable than a traditional approach.” – Catherine

Do you consider it safe?

“Yes, but I wouldn’t recommend it if a client was diabetic or had certain other medical diagnoses.” – Karen
“IF wouldn’t be appropriate for someone requiring food at regular intervals, such as a diabetic. I also would definitely not recommend someone goes ‘cold turkey’ on an IF approach without support and guidance. Without working with a qualified, experienced healthcare provider, I would only recommend this pattern of eating to someone who already has a deep understanding of what nourishing diet is optimal for them, that they fully understand how to cope day to day and understand what signs to look out for that show they might not be suitable for it. Without this knowledge it could be extremely challenging for someone, especially if they are used to a more ‘ultra-processed’ diet and have swings of blood-sugar imbalances, for example.” – Catherine

Introduce us to the most common types of IF…

“The three most widely studied types of intermittent fasting are the 5:2 diet, daily time restricted feeding (TRF) and alternate day fasting (ADF).

5:2 Diet

  • 2 days a week: consume 500 calories each day (around 25% of a typical day’s food). These are known as fast days and can be whenever in the week you want them.

  • 5 days a week: the remaining days are feast days on which you consume a nutrient-dense, nourishing diet with no calorie restriction.


  • Consistently limit your eating ‘window’ to a certain period of time (usually 6-8 hours) every day.

  • For example, each day only eat between 10am and 6pm, consuming a nutrient-dense, nourishing diet in that window with no calorie restriction. For the remaining 16 hours, it’s water or herbal teas.


  • Day 1: consume approximately 500 calories. This is a fast day.

  • Day 2: consume a nutrient-dense, nourishing diet with no calorie restriction. This is a feast day.” – Catherine

What are their advantages?

“TRF is the most popular, perhaps because it’s the most flexible – you can move your window around to suit your lifestyle – and thus the easiest to stick to. However, weight loss can be around 1lb a week – or 50% slower than for the 5:2 or ADF. With the latter two, anyone with a BMI over 40 could lose weight by 3-4lb a week.” – Catherine

Although Intermittent Fasting has actually been practised for centuries, it’s seen a revival in recent years as a practice that promotes health, particularly in relation to healthy ageing.
Catherine Sharman

What are the benefits?

“Weight loss, improved cognitive function and anti-ageing. Telomeres are small structures that protect the end of your chromosomes. Shortening telomeres is a marker of ageing, but IF could help maintain telomere length.” – Karen
“Although the effects of IF in the general population continue to be controversial, it is being shown to have an impact on health. Following a pattern of IF can help with lowering overall calories consumed, encouraging an intake of nutrient dense food, helping weight loss and lowering the risk of susceptibility to chronic health concerns such as heart disease and type 2 diabetes. Additional health benefits include improved detoxification, improved blood sugar and hormone regulation, blood pressure control and reduced inflammation.” – Catherine

Any common downsides?

“There can be some initial tiredness simply because, with some IF models, you are consuming fewer calories.” – Karen
“The first days can be challenging and lead to headaches (you need to stay hydrated on fasting days), irritability, a reduced ability to concentrate and, possibly constipation. But these initial side effects usually disappear. IF can also lead to overeating on feast days, as a ‘reward’ for compliance on the fast days. It’s also crucial with IF to understand what a nourishing diet looks like. Simply following an IF eating pattern will not compensate for someone eating food that’s empty of nutrients, that they’re intolerant to, that causes digestive issues or that doesn’t give them the specific nutrients to support a stressful lifestyle or intense exercise, for example. The eating pattern itself may be challenging to sustain for someone who is used to grazing.” – Catherine

How can you tell if IF is right for you?

“If you feel energised and lose weight after trying it!” – Karen
“Understand the downsides and cautions, as well as what a nourishing diet looks like for you. You will also need to think about how receptive you will be to a change in eating pattern. Will you also be metabolically flexible enough to not eat for long periods without showing signs of blood sugar dysregulation? Finally, you must be prepared to pay attention to how you feel. If IF makes you feel stressed, weak or ill, try shortening your fast or stopping altogether.” – Catherine

Where should a novice start with IF?

“Proceed with caution – and get advice and support from a qualified healthcare provider with IF experience. You could then begin with the approach of simply following the pattern of three meals a day without the need for snacking and see how you feel. If you feel the effects of blood sugar imbalances (dizziness, feeling uncomfortable, stressed, irritable, tired, faint etc) divide your meals up into six small meals. Gradually, over a period of several months, you can then reduce the window during which you consume food each day with the intention of fasting for 16-18 hours a day (TRF) or lengthening the gaps between meals (ADF).” – Catherine

How quickly can you expect results?

“Currently science hasn’t shown how long someone should follow an IF approach to achieve a therapeutic benefit. There are too many variables, such as current weight, eating pattern,  compliance, food intake and individual health concerns.” – Catherine 

What are the best ways to break a fast?

“Eat a balanced meal with protein (eggs, meat, fish or seeds) and plants (a rainbow of vegetables).” – Karen
“What you eat the day before going into a fast is as important as what you eat after coming out of it. Ensure both these meals are filled with quality protein, essential fats, complex carbohydrates and are dense with micronutrients.” – Catherine

Any tips for making IF easier? Dealing with hunger cravings, for example…

“Cinnamon can help with sugar cravings as can including a protein serving (meat, fish, dairy, eggs) with each meal and snack.” – Karen
“Always have a plan, so you have structure and all the nourishing food you need at your fingertips. If it’s challenging to avoid particular treats, try removing them from easy reach. Being hydrated will also tell you whether you really are hungry or just dehydrated. Have a glass of water (250ml) or herbal tea every hour.” – Catherine

Does your exercise regime need to change if you’re on IF?

“No. Exercise will maintain muscle which is more metabolically active than fat.” – Karen
“You might just find your body takes time to adapt to your new eating regime. After that adjustment period you might find you have more energy to exercise, especially if you are eating nutrient-dense foods – including quality protein with each meal and doing some resistance training should help you avoid losing muscle mass.” – Catherine

Is there anything older women in particular need to consider before trying IF?

“I would not try it without professional guidance if you are stressed or diabetic, or have a hormonal imbalance. Our stress hormone, cortisol, rises when we are stressed. It follows the same pattern as insulin, the well-known hormone that helps to control our blood sugar balance. If cortisol and insulin are both high, as they are in diabetes and in hormonal imbalance, then your body believes there is an immediate threat and holds onto food supplies for safe keeping for energy (typically around your mid-section). This could render IF less effective for weight loss.
“If you were to work with a registered nutritional therapist or another health professional, they would likely work first on lowering the body’s stress response in stressed clients or those with hormonal changes (during the menopause, for instance). Once the body is back in parasympathetic nervous system mode (i.e. it’s in ‘rest and digest’ mode rather than ‘fight or flight’), then it’s more likely IF will be effective because the body will not react by storing fat as glycogen and will instead focus on burning excess, hopefully resulting in weight loss.” – Karen
“During the menopause, metabolism changes and slows down. This can be due to the levels of estrogen and progesterone falling out of balance. This relatively sudden hormonal fluctuation tends to cause many women to gain weight and reduce muscle tissue. IF may help with various symptoms of menopause, and can be a helpful tool for managing weight loss and avoiding insulin resistance (another common symptom of menopause). Because IF has been shown to improve metabolism, it could be more effective at sparing muscle mass compared to ongoing calorie-restriction diets.” – Catherine

Any final words of wisdom?

“IF can be exceptionally effective, but go slow and seek professional help.” – Karen
“Look carefully at the research because there are a lot of super-inflated claims about IF in blogs and on social media. At this point, the mechanism and benefits of IF are unproven. There are no studies showing this way of eating cures cancers, extends lifespans or has any anti-ageing effects.” – Catherine
For more information, head to the Institute for Optimum Nutrition and Après Food Co.
DISCLAIMER: Features published by SheerLuxe are not intended to treat, diagnose, cure or prevent any disease. Always seek the advice of your GP or another qualified healthcare provider for any questions you have regarding a medical condition, and before undertaking any diet, exercise or other health-related programme.

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