Dr Desmond Wai, gastroenterologist at Mount Elizabeth Novena Hospital, explains fasting and its effectiveness for detox, weight loss and other health conditions.
From a nutritional standpoint, what is fasting?
Fasting means going without food or drink for a period of time. While fasting has been practised for religious reasons throughout the centuries, it is becoming an increasingly popular tool for weight loss.
Daily, an average person requires about 22 kcal of food calorie intake per kg of body weight. Thus, an 80 kg man would require about 1720 kcal per day. To lose weight, an individual must take in less calories than they expend.
Most low calorie diets suggest a calorie intake of about 800 – 1200 kcal a day. A very low calorie diet is generally defined as daily calorie intake of less than 800 kcal and that can be done by fasting, ie. not eating for several hours and eating very little in a day.
Is fasting a good way to detox?
A healthy person does not need to detox. Our kidneys and liver will get rid of toxins for us no matter what or when you eat.
It is only patients with kidney failure or liver cirrhosis that may require dialysis or special medications for detox.
Is fasting effective for weight loss?
Very low calorie diets have been assessed in clinical studies regarding their effectiveness for weight loss. The rationale is that the lower the calorie intake, the more rapid the weight loss.
Studies compared conventional diets with very low calorie diets of the intermittent fasting type. Results showed that while very low calorie diets lead to greater short-term weight loss, there is no difference in long-term weight loss.
Additionally, there are problems with starving or taking very low calorie diets.
- There is substantial protein loss that will reduce muscle mass
- There may be drop in blood pressure and blood glucose levels so patients with hypertension or diabetes would have to adjust their medications
- Many dieters have complained of hair loss, thinning of skin, and feeling of coldness
- There may be an increased risk of forming gallstones
- It is unsustainable
- After a prolonged period of fasting or starvation, there will be surge in hunger-inducing hormones that lead to craving of food. This explains why after a period of fasting, patients may end up eating more!
Can fasting improve health or help with medical conditions?
Yes, fasting helps control certain medical conditions. Taking a low calorie diet helps improve body weight, glucose and blood pressure control. Weight loss also helps to control other conditions like lower limb joint pains, fatty liver, gastroesophageal reflux disease, etc.
Does fasting cause our metabolism to slow down or our body to store fat?
You might have heard that the body holds onto fat in response to long periods of no food. While fasting may not cause the body to store fat, it does lead to lower muscle mass and metabolism rate.
Restricted calorie intake leads to breakdown of stored fat as well as protein. Though the person would lose weight, they also lose muscle mass which leads to a slowing down of metabolism.
For individuals looking to lose weight, a healthier way is to combine a low calorie diet with exercises which would then help to retain the body's muscle mass.
What are the side effects of fasting or a low calorie diet?
Taking very low calorie diet can lead to many side effects. Side effects include a drop in blood pressure and glucose levels, feeling cold and lethargic, hair loss, constipation, halitosis, muscle cramps and diarrhoea.
Is fasting recommended for certain groups of people?
Yes. For obese and overweight patients, taking a low calorie diet combined with exercise and behavioural modification is important to achieve weight loss.
Occasionally, we do advise patients to go on very low calorie diets for special occasions. A typical example is when an obese patient is planning for elective surgery. Taking a very low calorie diet helps them to reduce weight fast, reducing their risks in surgery.
What is a safe recommended frequency and length for fasting?
People who wish to lose weight should consult their doctors and/or dietitians to come up with a feasible weight management programme. Taking a low calorie diet alone leads to some undesirable side effects and is difficult to be sustained. We thus recommend a 3-pronged approach:
Diet – This would involve taking a low calorie diet that is high in protein and low in unhealthy fats such as trans fat. The diet should also consist of more of complex carbohydrates like brown rice and wholemeal bread, and less of simple carbohydrates like soft drinks.
Exercise – This would involve a combination of aerobic exercises (eg. running, swimming, brisk walking) and resistance training (eg. push-ups). Exercises should be done for 30 minutes a day.
Behaviour modification – Goal setting and keeping a food diary can help in modification of eating behaviour. Binge eating triggers can be identified and controlling cues can be implemented. Social support and reminders from friends and family is also important in behavioural modification.
