A young woman, aged 25, chose an intermittent fasting schedule of 36 hours to drop her weight. She weighed 95 kg, had a BMI (body mass index) of 34 and thought this was the best way to get off the weight cliff. “At the end of a month, she lost 5 kg but she had extreme fatigue, lack of concentration, bloating, acidity and sleep issues,” says Dr Richa Chaturvedi, endocrinologist at Indraprastha Apollo Hospital, Delhi. Although many celebrities — the latest one being Bollywood actor Akshay Kumar — follow this diet fad, is it double-edged?
What is a 36-hour fasting routine?
A 36-hour fast is considered an “extended fast” — for example, stopping after early dinner on Sunday and eating again at breakfast on Tuesday. In between one can have water, tea and calorie-free drinks to keep the weight off. During this time of calorie-deficit, the body switches from using food for energy to burning up stored fat for energy, resulting in weight loss. This is also called the 5:2 diet which involves eating normally for five days per week, then restricting calorie intake to just 300–500 calories on the other two days.
What changes happen in the body?
After about 12 hours of not eating, your body uses up most of its stored sugar (called glycogen). “When this happens, your insulin levels fall. This is important because high insulin can lead to fat storage. Lower insulin helps your body start burning fat for energy instead,” says Dr Sudeep Khanna, gastroenterologist.
Once glycogen stores are low (usually after 18–24 hours), your body starts breaking down stored fat into molecules called fatty acids and ketones. “Now ketones can fuel the brain and body when no food is available. This is called ketosis,” explains Dr Khanna.
This is followed by autophagy, which is your body’s way of cleaning out old, damaged cells and recycling parts to make new ones. Research suggests that autophagy may start increasing after about 24 to 36 hours of fasting, though this depends on the person. “It’s thought to help protect against diseases like cancer and Alzheimer’s but more human studies are needed,” adds Dr Khanna.
Some people report feeling more focussed during a fast. This may be due to stable blood sugar, fewer digestive demands and ketones providing steady energy for the brain. However, others may feel tired or irritable, especially early on.
“You might feel hungry at the usual times you eat but it often fades after 18–24 hours. This is because the hormone ghrelin, which causes hunger, rises and falls in waves,” says Dr Khanna.
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Is this fasting format safe?
He finds this format safe for most healthy adults, provided one is well-hydrated and not overdoing physical activity. However, he does not recommend it for people with diabetes, eating disorders, pregnant women or those taking certain medications — unless under medical guidance.
What are side effects?
Dr Chaturvedi has seen too many risks of prolonged fasting among her patients. “Prolonged or excessive fasting can lead to the body burning fat for energy. This produces an excess of ketone bodies, water-soluble molecules produced by the liver when glucose is scarce. These tend to be acidic. Lack of hydration may lead to electrolyte or mineral imbalances. That’s why most people experience dizziness and headaches during the initial period of fasting. Fatigue, insomnia, lethargy and sluggishness are frequent,” she says.
But it is the loss of muscle mass, digestive issues, mood disorders and inflammation that she finds as more concerning.
What are checks and balances?
Fasting should not be followed by binging, warns Dr Chaturvedi. Dr Khanna suggests watching out for metabolism. “Going for extended periods without eating might actually encourage your body to start storing more fat in response to starvation,” he says. In fact, other forms of fasting with a wider eating window can be easier to follow.
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