The intermittent fasting regimen involves fasting for certain hours of the day, or for entire days, consecutively or not. PHOTO: ISTOCKPHOTO

The diet fad involves fasting for certain hours or for entire days; doctors stress that little is known about the method's effects beyond six months, its sustainability and safety

Unless you hide under a rock or live in a cave, you will have heard of the latest lifestyle craze - intermittent fasting (IF). Members of your family are doing it, and so are your friends, gym buddies and maybe even your doctor.

The regimen involves fasting for certain hours of the day, or for entire days, consecutively or not. Some people go on it to lose weight and say they are smaller around the waist too. Others do it to feel energetic and focused.

IF has also been touted as a way to keep blood sugar in check and trigger autophagy. This is the process where the body regenerates itself on a cellular level. It is said to protect against diseases such as Parkinson’s and some forms of dementia, decrease inflammation in the body and prolong a person’s lifespan. Fasting, intensive exercise and a low-carbohydrate diet are said to promote the process.

Doctors and dietitians at the Singapore General Hospital (SGH), National University Hospital (NUH) and Khoo Teck Puat Hospital (KTPH) told The Sunday Times that they have had more patients asking them about fasting.

However, the doctors also said that not enough research has been done on IF for them to recommend it.

Studies have been small-scale and done mainly on overweight subjects and animals. Not much is known about the effects of IF beyond six months, its sustainability and safety.
Yet, doctors are not dismissing it. They said the best kind of diet is a safe and nutritionally sound one that a person can stick to.

Dr Tham Kwang Wei, senior consultant at SGH’s Department of Endocrinology and director of its Lifestyle Improvement & Fitness Enhancement Centre, said: “We are not ruling it out.

She sees it as a tool, among others, for weight loss.

"It is definitely an option," she said."But it must suit the patient and it must be something he can stick to. Adherence is key."


By all accounts, humans have fasted for millennia and are hardwired to survive periods of time without food. Cavemen and women fasted by default because they did not have a constant supply of food. People also fast for religious reasons.

Dr Benjamin Lam, consultant at KTPH’s Department of Family and Community Medicine, said: "Physiologically, we were programmed to have periods of fasting. We were built that way. The constant supply of food happened only 40 to 50 years ago."

IF became popular in 2012, after a BBC Horizon documentary called Eat, Fast & Live Longer, presented by Dr Michael Mosley, aired. The British presenter and producer went on to write best-selling books such as The Fast Diet (2013).

Books such as The 5-2 Diet Book (2012) by British journalist Kate Harrison; The 2-Day Diet (2013) by British scientists Dr Michelle Harvie and Professor Tony Howell; and The Obesity Code: Unlocking The Secrets Of Weight Loss (2016) by Dr Jason Fung, a Canadian nephrologist, also popularised the trend.

Fasting has also taken off in Silicon Valley in the United States. Technology industry types are using it as a form of biohacking to enhance productivity and work performance. Bloomberg has reported that start-ups offering meal deliveries, fasting programmes and supplements are trying to cash in.

With IF, people choose one of several ways to abstain from food.

There is the 16-8 method, where they give themselves a window of eight hours during which they can eat. Some choose to skip breakfast and eat lunch and dinner, others eat breakfast and lunch, and skip dinner. The idea is to not eat for 16 continuous hours.

Another method is 5-2, where people have a very low calorie diet of about 600 calories for two days, either consecutively or not, and eat normally on the other five days of the week.

Other methods include fasting on alternate days or fasting for 24 hours once or twice a week. While fasting, they should stay hydrated with water.


The doctors and dietitians interviewed said that during IF, the window for eating is restricted so people tend to consume fewer calories and therefore lose weight; and the fasting time allows the body to follow its natural circadian rhythms.

Dr Kalpana Bhaskaran, domain lead for Applied Nutrition & Glycemic Index Research at Temasek Polytechnic and vicepresident of the Singapore Nutrition & Dietetics Association, said: "Your window to eat is restricted, so automatically, there is a calorie deficit."

She estimated that people on the 16-8 method of IF eat about 300 fewer calories a day.

The body’s circadian rhythm, the internal clock that regulates sleeping and waking cycles, gets a chance to settle and rest during the hours of fasting, doctors said.

When it is disrupted, SGH’s Dr Tham said, the body perceives it as stress, which can result in inflammation in the body. Inflammation can lead to chronic diseases and even cancer.

"You allow your body to process the nutrients you take in, for 16 hours, instead of feeding it constantly," she said.

She added that there is increasing evidence to show that the circadian rhythm sets the body to metabolise nutrients differently at different times of the day.

At night, for example, for the same amount of nutrients consumed, the body may tend to "hang on" to glucose and fat more and longer, and this may lead to weight gain and higher blood glucose and fat levels after meals and the following day.

Like other weight-loss plans, IF may not work for everybody. The ones who might be able to tolerate it, doctors said, are those who skip breakfast as a habit and people who do not graze or snack throughout the day.

Dr Asim Shabbir, director and senior consultant of NUH’s Centre for Obesity Management and Surgery, said: "IF would work for those who observe strict dietary rules of consuming significantly fewer calories than they normally do. If they don’t and continue to eat well above their needs either before or after the fast, they may actually find themselves gaining rather than losing weight."


A study of 19 overweight Chinese patients, done at KTPH in 2015, shows that IF can yield some positive results.

Dr Lam said he decided to do the study after a year-long master’s course in obesity management in the United Kingdom, where Dr Harvie, one of the authors of The 2-Day Diet, spoke. He wanted to see if fasting worked for overweight patients here.

The Chinese subjects, drawn from the hospital’s weight-management clinic, were divided into two groups in the 12-week randomised controlled trial. Ten of them were in a control group and received general diet and exercise advice.

Nine patients went on the 5-2 regimen, fasting for two consecutive days a week. They could pick which consecutive days to fast, but were asked to stick to those same two days throughout the trial.

On fasting days, they had three packets of Optifast, a meal replacement product that is mixed with water to make a shake, two scoops of protein powder and one multivitamin supplement. It added up to 540 to 570 calories.

For days when they were not fasting, they were given advice on healthy options for meals and had to fill out a food diary.

Three significant results emerged from the trial.

The fasting group lost 3.9kg on average over the 12 weeks, compared with 0.5kg for the control group, after adjusting for initial body weight.

"The weight loss happened mainly in the first two months," said Dr Lam, who presented his findings at the 25th European Congress on Obesity in Vienna in May this year. "This has implications. Can people maintain the weight loss?"

The fasting group was also smaller around the waist and hip. On average, they lost 3.6cm off the waist and 3.3cm off the hips.

Another promising result was that the fasting group had lower levels of liver enzymes. Elevated levels have been associated with liver inflammation or damage.

Dr Lam said: "Most people got used to fasting and naturally became very conscious of what they ate on non-fasting days. The evidence so far seems to show that intermittent fasting is safe and can result in weight loss. If patients want to try it, we get dietitians to make sure their diet is nutritionally sound."

More studies need to be done, he said, adding that he hopes to do a larger-scale one involving more subjects, from different racial groups, who fast for longer than three months.

Researchers still do not know the effects of IF on people of normal weight and how and whether it works or is safe and sustainable over the longer term, say, for instance, more than one year.

Dr Lam said: "The causes of obesity are different. It’s a complex disease. What works for each patient is different."


The word "over-compensation" comes up a lot in interviews with doctors and dietitians, who said that some fasters might binge during their eating window or on non-fasting days.

Dr Khoo Chin Meng, senior consultant and head of the Division of Endocrinology at NUH, said: "People who are on IF have to do it right, with the right motives. There are some success stories, but it is not sustainable for a lot of people. IF aims to lose body weight by reducing total calorie intake and it is important for the fasters to recognise this and the need to eat healthily and not binge-eat.”

Ms Pamela Er, a senior dietitian at the hospital, said IF will not work if fasters skip breakfast and then eat a high-calorie lunch.

“I warn patients about bingeeating, especially those who eat when they are upset.”

Like the other dietitians interviewed, she said people should focus on meals with complex carbohydrates, such as brown or basmati rice – both of which can help them feel full for longer; lean  protein; and fruit and vegetables.

Life can also get in the way of IF. Ms Er said: “If they are meeting friends for dinner and everyone is late, dinner might be past the eating window. That’s one big challenge.” Dr Khoo also said that some people might think they should refrain from drinking while fasting.

"Hydration is important throughout the day," he said, adding that people should be drinking 2 to 2.5 litres of water.

All of them said that some people should not fast: pregnant women, people with kidney problems, liver cirrhosis, low blood pressure, mental disorders and nutritional deficiencies. Diabetics need to consult their doctors because they are in danger of hypoglycemia, where their blood sugar dips too low.

They advised anyone looking to do IF to consult their doctors first.


Dr Ng Chin Hin, a haematologist at the National University Cancer Institute, Singapore, said he started IF after hearing about it from a colleague. Dr Ng started running last year and was discussing how to build endurance.

He read up about IF and decided to try it, starting in March this year. Since then, he has lost 20kg and his weight hovers around 68 to 70kg. He continues with IF not for weight loss, but because he feels it gives him clarity and focus.

On Mondays, Tuesdays and Thursdays, his eating window is from 6 to 9pm and he has just one meal on those days. He said he eats what his wife cooks, meals with meat, vegetables and soup; plus fruit, yogurt and nuts. On Wednesdays and Fridays, he fasts for 16 hours and has an eating window of eight hours. On Saturdays and Sundays, he eats normally.

He couples IF with intensive exercise, running 40 to 50km a week, including a long run of 20km or more on Saturdays.

IF is flexible and accommodates his schedule and lifestyle, he said, adding that he has long clinic hours on Mondays and Tuesdays and his IF schedule gives him an extra hour to see patients as he skips lunch.

The 44-year-old also said he was never one who needed breakfast.

"We force ourselves to eat breakfast because people say it’s the most important meal of the day," he said. He said there was potential in IF.

"Now when I fast, I feel clearer, my mind is more focused," he said. "Most people feel tired by 6pm, but I don’t."

Strategy and capital consultant Monish Chainani, 49, finds IF equally flexible.

He said he likes snacking in the night, so his eating window is from 4pm to midnight. He has been doing IF since June this year. His weight is 76kg now, down from 83kg. Before IF, he said he had tried many ways to lose weight- from taking supplements to following a low-carbohydrate diet to working out.

On IF, he has his biggest meal at 4pm, starting with a banana milkshake or a smoothie, and also eating bread and cereal.

"By dinner time, I can’t eat a heavy meal and I eat what my wife cooks - vegetables, a little meat," he said, adding that he might snack on a packet of chips and have chocolate. "I am not controlling what I eat, I control my lifestyle."

He wants to lose 2kg more, but finds the going more difficult. Gone is the dramatic weight loss that he experienced initially.

What sealed the deal for Ms Malti Peplow, 43, a retail specialist, was that she and her 63-year-old husband began to enjoy better health after they started IF.

They have been at it since September this year. Both of them have lost weight; she has lost 8kg and her husband, a British businessman, has lost about 12kg. Her body measurements are down and her eczema is gone. She said her husband "shocked himself" when he got his cholesterol and blood pressure levels down.

In addition to restricting their eating hours, they also fast for 24 hours once a week. Their focus is on nutritious meals with carbohydrates, protein and vegetables, snacks such as hummus or tuna, and both take supplements and drink protein shakes. They also work out in a gym five days a week and adjust IF around their work and travel schedules.

She said: "A lot of the time, we eat for the sake of eating. What this has taught me is to eat when I’m hungry. I never thought I’d be able to fast.

"All the diets I’ve tried, all the money I’ve wasted... this has been the most sustainable. I can see the results. Friends say I’ve shrunk and I look healthier."

On the flip side, chef Willin Low, 46, did IF in January and February this year. He said he had acid reflux, a burning pain in the chest, every night when he was in bed.

"The pain was terrible. I thought it might have been alcohol, but I cut that out and the reflux continued. It disappeared only when I stopped IF."


  • Pregnant women
  • Kidney patients
  • Patients with liver cirrhosis
  • People with low blood pressure
  • People with mental disorders
  • People with nutritional deficiencies
  • Diabetics