16:8, 5:2, these are popular methods of intermittent fasting. But how safe is it? Is it suitable for everyone and what precautions are needed? Dr Lee Phong Ching, Senior Consultant, Department of Endocrinology at Singapore General Hospital (SGH), answers.
What is intermittent fasting?
While other diets focus on what to eat, intermittent fasting (or IF for short) focuses on when you eat. It doesn’t specify the foods you should eat but rather when you should eat them. In this respect, it’s not a diet in the conventional sense but rather a useful tool to adjust eating patterns.
“The idea behind intermittent fasting (IF) is that by providing structure and limiting the amount of time the person spends eating, total calorie intake will be reduced and weight loss can be achieved,” explained
Dr Lee Phong Ching, Senior Consultant from the
Department of Endocrinology at
Singapore General Hospital (SGH), a member of the
SingHealth group.
“Even while following IF, it is crucial to eat a healthy, well-balanced diet. Staying hydrated is also important – a person should be drinking about two litres of water daily.
If you have a medical condition, you should consult with your doctor before trying intermittent fasting,” Dr Lee added.
Popular intermittent fasting methods
1. 16/8 method
This method involves fasting for 16 hours a day, leaving an 8-hour window during the day to eat food normally. Some choose to skip breakfast and eat lunch and dinner; others choose to eat breakfast and lunch and skip dinner. Many find it easy to stick with this pattern over the long term.
2. 5:2 approach
In 5:2, you eat normally for five days a week, then cut back to 20 percent of your normal daily calorie intake (500 – 600 calories a day) for the other two days. The two days of caloric restriction can be achieved using specially formulated meal replacements. You can discuss with your doctor or dietitian on available options.
Are there side effects to intermittent fasting?
At the start, you may feel weak and have difficulty concentrating due to hunger. However, this should only be temporary, as it can take some time for your body to adapt to the new meal schedule.
As for the long-term effects of intermittent fasting, not much is known about its effects beyond six months, its sustainability and safety.
How to fast safely
If you want to do intermittent fasting, there are precautions you can take to ensure it does not harm your body.
Do not fast for over 24 hours as it can lead to dehydration, irritability, fainting, lack of energy and inability to focus
Maintain a well-balanced, healthy diet during your eating periods. Include complex carbohydrates like brown rice to feel full longer, lean protein, and fruits and vegetables. Watch the amount of food you eat during the eating periods (do not binge-eat).
Stay hydrated by drinking a minimum of 8 cups of water daily (equivalent to a total of at least two litres). Water is allowed during the fasting period.
Do not overexert yourself when fasting (especially during exercise)
If you feel unwell for any reason, stop fasting and seek medical help
Who should not do intermittent fasting?
Intermittent fasting is not safe for everyone. Those who
should not do it are:
Pregnant or breastfeeding women
Patients with kidney problems.
Patients with
liver cirrhosis
Patients who have any medical conditions (such as
diabetes or
high blood pressure) or who are on any medications are advised to seek advice from their doctor before embarking on an intermittent fasting program.
People with low blood pressure
People with mental disorders (such as
eating disorders)
People with nutritional deficiencies
People with diabetes who are on insulin or drugs that can cause
hypoglycemia (low blood sugar).
Ref: K21
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