- Kunal Kemmu lost weight using 24-hour water fasting, highlighting its popularity among actors
- Water fasting means consuming only water for set periods, unlike intermittent or modified fasting
- Fasting causes weight loss by calorie restriction, shifting energy use from glycogen to fat
When actor Kunal Kemmu recently revealed that 24-hour water fasting helped him lose weight, from 80 kg to 71 kg, the practice once again found itself in the spotlight. He's not alone. Actors, including Henry Cavill while on The Graham Norton Show, have spoken publicly about incorporating periods of fasting into their fitness regimens, often under professional guidance, to achieve specific physique goals before filming or competition. In fact, in the world of professional bodybuilding, strategic dehydration is done before competitions to nail that chiselled and well-defined look.
But while celebrity transformations often make fasting appear simple, doctors caution that water fasting is not a shortcut to sustainable weight loss. Unlike intermittent fasting, which usually allows eating within specific time windows, water fasting involves consuming only water for a set period, typically 24 hours or longer. Although some research suggests it may improve insulin sensitivity, promote fat utilisation and trigger cellular repair pathways, the benefits are closely tied to the duration of the fast, an individual's health status and whether it is medically supervised.
Experts emphasise that what works for a healthy, highly monitored athlete preparing for a role or competition may not be appropriate, or safe, for the average person.
What Is Water Fasting?
Water fasting is exactly what it sounds like: abstaining from all food while drinking only water.
It differs from:
- Intermittent fasting: Eating during defined windows (such as 16:8)
- Time-restricted eating: Limiting meals to a certain number of hours each day
- Modified fasting: Allowing a small number of calories
A 24-hour water fast generally means finishing dinner one day and not eating again until dinner the next day.
Why Do People Lose Weight During Water Fasting?
The answer is straightforward: calorie restriction. Without food intake, the body first uses stored glycogen for energy. As glycogen stores become depleted, the body gradually shifts towards using fat as fuel, producing ketones in the process.
Research published in Nature Metabolism found that during prolonged fasting, the body switches from glucose to fat metabolism within the first two to three days. Researchers also observed molecular changes across multiple organs after about three days of complete calorie restriction, suggesting that some biological effects extend beyond weight loss. However, these findings came from closely monitored healthy volunteers and should not be interpreted as an endorsement of unsupervised prolonged fasting.
Why Even Bodybuilders And Actors Don't Overdo It
Celebrity transformations can create the impression that fasting is a daily lifestyle. In reality, bodybuilders and actors generally use fasting strategically and temporarily, often:
- Before a photoshoot or competition
- Under the supervision of nutritionists
- Alongside carefully planned protein intake
- With structured resistance training
- While closely monitoring hydration and recovery
For someone like Henry Cavill, who has spoken about following highly disciplined nutrition plans for physically demanding roles, fasting is just one small component of an overall programme, not a standalone weight-loss strategy. Similarly, Kunal Kemmu's reported 24-hour water fast formed part of a broader lifestyle change rather than acting as a magic solution.
What Are The Potential Benefits?
According to experts, calorie restriction and fasting are being actively studied for their effects on metabolism, ageing and chronic disease risk. Human research remains ongoing, and long-term health benefits are still being investigated.
Some studies suggest that carefully planned fasting may:
- Improve insulin sensitivity
- Promote fat oxidation
- Reduce overall calorie intake
- Support modest weight loss
- Trigger autophagy, a cellular recycling process that is mainly observed after more prolonged fasting
However, much of the evidence for autophagy in humans is still emerging, and experts caution against overstating these benefits.
The Risks You Shouldn't Ignore
Water fasting isn't suitable for everyone.
Potential side effects include:
- Dizziness
- Fatigue
- Headaches
- Low blood pressure
- Dehydration
- Electrolyte imbalances
- Muscle loss
- Difficulty concentrating
Longer fasts can also increase uric acid levels and affect kidney function markers. A recent case report of prolonged water-only fasting found significant changes in several blood parameters, highlighting the need for caution and medical supervision rather than suggesting such fasting is safe for the general population.
Who Should Never Try Water Fasting Without Medical Advice?
Doctors generally advise against water fasting for:
- People with diabetes taking insulin or glucose-lowering medicines
- Pregnant or breastfeeding women
- Children and adolescents
- Older adults with frailty
- Individuals with eating disorders
- People with chronic kidney disease
- Those with low blood pressure
- Anyone taking medications that require food
Even healthy adults should consult a healthcare professional before attempting prolonged fasting.
Is Water Fasting Better Than A Balanced Diet?
Not necessarily. Most major organisations, including the World Health Organization (WHO), continue to recommend sustainable eating patterns built around:
- Fruits and vegetables
- Whole grains
- Pulses
- Healthy fats
- Lean protein
- Regular physical activity
These habits have consistently been shown to reduce the risk of obesity, diabetes and cardiovascular disease. Rapid weight loss through fasting may be followed by weight regain if healthy eating habits are not maintained.
Water fasting has gained attention because of celebrity endorsements and social media trends, but it isn't a miracle weight-loss method. A carefully planned 24-hour fast may be appropriate for some healthy adults under professional guidance, but longer or frequent water-only fasts carry real risks and are not suitable for everyone.
The reason elite athletes and actors don't rely on water fasting alone is simple. Lasting body composition changes come from consistent nutrition, strength training, adequate sleep and recovery, not from skipping meals indefinitely. For most people trying to lose weight, experts agree that sustainable lifestyle changes remain the safest and most effective approach.
Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.