Kitchen Medicine
Is a Water Diet Harmful? The Risks of Water Fasting
A water diet can be harmful. Most of the weight lost is muscle and water, and it returns quickly. It carries risks of electrolyte disturbance, gallstones and gout.
Translated from the Turkish original by DoktorClub. The Turkish version is the reference text; this English translation has not been separately reviewed by a physician. Read the Turkish original.
Key takeaway
Yes, a water diet done on your own can be harmful. The Turkish Ministry of Health's Türkiye Nutrition Guide (TÜBER 2022) lists starvation diets providing less than 200 calories a day among diets that are risky to health. A large share of the weight lost on these diets is muscle and water, and it comes back quickly. People using insulin or glucose-lowering pills, pregnant women, children and people with kidney disease should not do a water fast on their own. Balanced calorie reduction is safer for lasting weight loss.
Short Answer
Yes, a water diet done on your own can be harmful. The Turkish Ministry of Health's Türkiye Nutrition Guide (TÜBER 2022) lists starvation diets providing less than 200 calories a day among diets that are risky to health. A large share of the weight lost on these diets is muscle and water, and it comes back quickly. People using insulin or glucose-lowering pills, pregnant women, children and people with kidney disease should not do a water fast on their own. Balanced calorie reduction is safer for lasting weight loss.
What is a water diet (water fast)?
A water diet means eating nothing and drinking only water for a certain period. It is also popularly called a "water fast" or "detox fast." It can last from one day to several weeks.
TÜBER 2022 classifies diets by energy content. Those providing 200–800 calories a day are very-low-calorie diets. Those below 200 calories are considered starvation diets. Drinking only water falls into this most extreme group.
This method is not the same as intermittent fasting. In intermittent fasting, food is eaten at certain hours. In a water fast, no food is taken for days.
Why is the weight lost not fat? Water and muscle loss
On a water fast the scale drops quickly, but most of the loss is not fat. A review published in Nutrition Reviews in 2023 examined prolonged fasts of 5–20 days, including water fasting. In these fasts, body weight fell by 2–10%. About two-thirds of the loss was lean mass (including muscle) and one-third was fat.
In several studies in the same review, metabolic improvements such as blood pressure were not lasting. None of these benefits persisted 3–4 months after the fast ended. This was the case even in people who maintained their weight.
TÜBER 2022 also states that rapid weight losses are regained in a short time. According to the guide, muscle loss slows basal metabolism. This makes it harder to keep the lost weight off.
What are the risks of a water diet?
TÜBER 2022 lists the side effects of very-low-energy diets system by system:
- Nervous system: Headache, impaired concentration, irritability, fatigue.
- Heart and circulation: Rhythm disturbance (arrhythmia) and low blood pressure.
- Stomach and bowel: Nausea, vomiting, diarrhea, constipation, abdominal discomfort and gallstones.
- Other: Menstrual irregularity, kidney stones, hair loss, feeling cold and mineral-electrolyte imbalance.
TÜBER also notes that these diets can result in death. The TEMD Obesity Guideline 2024 also states that losing weight very quickly can lead to the following problems:
- Electrolyte disturbance: Low potassium (hypokalemia) is the most common.
- High uric acid (hyperuricemia): Carries a risk of attacks in people with gout.
- Gallstones: Rapid weight loss increases stone formation.
- Mental health: Depression and eating disorders.
For people with gout, the NHS advises avoiding crash diets. According to the NHS, becoming dehydrated can also trigger a gout attack.
Who should not do it?
The following people should not start a water fast or a very-low-calorie diet on their own:
- People with diabetes: In people using insulin or glucose-lowering pills, blood sugar can fall to dangerous levels. ADA 2026 recommends that these people be under medical supervision during fasting.
- Type 1 diabetes: According to the 2023 review, water fasting is generally not recommended because of the risk of ketoacidosis.
- People using SGLT2-class diabetes drugs: ADA 2026 does not recommend ketogenic eating in these people because of the risk of ketoacidosis. Water fasting also markedly raises ketone levels.
- Pregnant and breastfeeding women: TEMD 2024 does not consider very-low-calorie diets appropriate during this period.
- Children and adolescents: TEMD 2024 and TÜBER 2022 consider starvation-based diets inadvisable in this age group.
- Older adults: TEMD 2024 does not consider very-low-calorie diets appropriate as the sole source of nutrition for older adults.
- People with a history of eating disorders: Rapid weight loss can trigger an eating disorder (TEMD 2024).
- People with kidney disease, gout or heart rhythm disorders, and those using diuretics: Rapid weight loss can cause electrolyte disturbance, rhythm disorders and high uric acid (TEMD 2024). NICE CG32 lists diuretic use among the risk factors for refeeding problems.
If you take medication regularly, be sure to talk to your doctor before starting a fast. Do not stop your medication or change its dose on your own.
Drinking too much water is also harmful: water intoxication (hyponatremia)
Some people drink very large amounts of water to suppress hunger. According to TÜBER 2022, water intoxication is rare. It occurs when more water is drunk in a short time than the kidneys can excrete. In this case, sodium in the blood falls (hyponatremia).
According to TÜBER, symptoms of hyponatremia are mental confusion, nausea and muscle spasms. The risk is higher in people with kidney disease and in those doing heavy exercise for long periods in the heat. Because no salt is taken in from food during a water fast, this balance is thought to be more easily disturbed.
TÜBER 2022 gives the total fluid requirement for adults as 2.5 liters a day for men and 2 liters for women. About 80% of this comes from beverages and 20% from food. The idea that "the more water, the more weight loss" is wrong.
Refeeding risk after prolonged starvation
When someone who has gone without food for days suddenly starts eating, the body's salt and mineral balance can be disturbed. This condition is called refeeding syndrome. NICE CG32 recommends starting nutrition slowly and at low energy in high-risk people. The guideline also recommends potassium, phosphate and magnesium supplementation and heart rhythm monitoring in these people.
The NICE CG32 guideline defines high-risk criteria for refeeding problems:
- Eating nothing or very little for more than 10 days is considered high risk on its own.
- Starvation for more than 5 days, combined with another risk factor, is also high risk.
- Other risk factors include a low body mass index and use of insulin and diuretics.
For this reason, coming off a prolonged fast should also be planned under a doctor's supervision.
Evidence-based alternatives
- Balanced calorie reduction: According to the TEMD Obesity Guideline, a daily deficit of 600 calories produces a loss of about 0.5 kg per week.
- An achievable goal: ADA 2026 targets a weight loss of at least 5–7% in people with overweight.
- Intermittent fasting: According to ADA 2026, it produces 3–8% weight loss over 8–12 weeks. It does not differ significantly from continuous calorie restriction.
- Lasting habits: TEMD 2024 measures success not by the weight lost in a short time but by the weight kept off over the long term.
Intermittent fasting is not suitable for everyone either. For details, see our guide on who intermittent fasting is suitable for.
What not to do
- Fasting while using insulin or insulin-secreting pills: Blood sugar can drop dangerously (ADA 2026).
- Stopping your medication on your own for a fast: Always discuss dose changes with your doctor.
- Drinking excessive water to suppress hunger: This can lead to hyponatremia (TÜBER 2022).
- "Losing weight" with diuretic teas, herbs or a sauna: According to TÜBER, these cause only water loss, not fat loss.
- Suddenly eating a heavy meal after a long fast: This can promote refeeding problems (NICE CG32).
- Putting a child or adolescent on a starvation diet: It is not suitable for young people in their growth period (TEMD 2024).
What does the evidence say?
Human studies on water fasting are few, and most are small. In some studies in the 2023 review, headache, insomnia, hunger and metabolic acidosis were observed. The authors consider prolonged fasting under controlled conditions moderately safe. However, they stress that the durability of metabolic benefits needs further research.
A retrospective chart review published in BMC Complementary and Alternative Medicine in 2018 examined 768 water-fasting visits. The fasts were done at a residential facility under physician supervision. 75% of the adverse events were mild. Still, in 212 visits the most severe adverse event was at a severe (grade 3) level, and serious adverse events occurred in 2 visits. These results cannot be generalized to unsupervised fasts done at home.
The claim that "a water fast cleanses the body of toxins" is not scientifically supported. The body already eliminates harmful substances through the liver and kidneys. For intermittent fasting and continuous calorie restriction, there are more randomized studies. In these studies, the two methods produce similar weight loss.
In Türkiye
- Official guide: TÜBER 2022 lists starvation diets and crash diets promising rapid weight loss in a short time among diets that are risky to health.
- Expert opinion: The TEMD Obesity Guideline 2024 recommends against using unscientific popular diets.
- Dietitian support: At the Ministry of Health's Healthy Life Centers, dietitians provide nutrition counseling to people with excess weight. Your family doctor can refer you to these centers.
- Emergency: In case of fainting, clouding of consciousness or chest pain, call the 112 Emergency Call Center (112 is the emergency number in Türkiye).
Which doctor should you see?
- First step: Your family doctor. They assess your weight goal, your medications and your test results.
- Nutrition plan: A dietitian; at Healthy Life Centers or hospital dietitians.
- If you have obesity or diabetes: Internal Medicine or Endocrinology and Metabolic Diseases.
- Suspected eating disorder: Mental Health and Psychiatry.
- Bring with you: A list of the medications you use, your latest test results and your weight change over the past 3 months.
When should you seek emergency care?
- Call 112 if fainting, clouding of consciousness, a seizure or chest pain occurs.
- Call 112 if you feel palpitations or an irregular heartbeat.
- Call 112 if confusion, severe headache, vomiting or muscle cramps occur after drinking a lot of water.
- If you have diabetes and your blood sugar drops below 70 mg/dL and does not recover, call 112.
- If marked weakness, shortness of breath or palpitations occur when you start eating after a fast, go to the emergency department without delay.
- If severe pain in the upper right abdomen, fever or yellowing of the eyes occurs, go to the emergency department without delay.
- If sudden joint pain with swelling and redness occurs, see a doctor the same day.
Related guides
- Who is intermittent fasting suitable for?
- What should people with diabetes eat?
- Low and high sodium
- Symptoms of gallstones
- Why is yo-yo dieting harmful?
- How to prevent muscle loss while losing weight
- Detox diets: myths and facts
- Kitchen Medicine and Metabolism guides
What changed? (October 2026)
- New guide: prepared according to TÜBER 2022, the TEMD Obesity Guideline 2024 and the ADA 2026 standards.
- Findings of the 2023 review on prolonged fasting and the refeeding risk were added.
Sources
- T.C. Sağlık Bakanlığı, Halk Sağlığı Genel Müdürlüğü. Türkiye Beslenme Rehberi (TÜBER) 2022. Yayın No 1031. https://hsgm.saglik.gov.tr/depo/birimler/saglikli-beslenme-ve-hareketli-hayat-db/Dokumanlar/Rehberler/Turkiye_Beslenme_Rehber_TUBER_2022_min.pdf (accessed October 7, 2026)
- Türkiye Endokrinoloji ve Metabolizma Derneği (TEMD). Obezite Tanı ve Tedavi Kılavuzu. 2024. https://file.temd.org.tr/Uploads/publications/guides/documents/obezitetanitedavikilavizu-2024.pdf (accessed October 7, 2026)
- T.C. Sağlık Bakanlığı, Halk Sağlığı Genel Müdürlüğü. Sağlıklı Hayat Merkezleri Rehberi. May 22, 2025. https://hsgm.saglik.gov.tr/depo/Shm_Rehber_22.05.2025.pdf (accessed October 7, 2026)
- Ezpeleta M, Cienfuegos S, Lin S, Pavlou V, Gabel K, Varady KA. Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutr Rev 2024;82(5):664–675. https://doi.org/10.1093/nutrit/nuad081 (accessed October 7, 2026)
- Finnell JS, Saul BC, Goldhamer AC, Myers TR. Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting. BMC Complement Altern Med 2018;18:67. https://pmc.ncbi.nlm.nih.gov/articles/PMC5819235/ (accessed October 7, 2026)
- NICE. Nutrition support for adults: oral nutrition support, enteral tube feeding and parenteral nutrition (CG32). Updated August 4, 2017. https://www.nice.org.uk/guidance/cg32/chapter/Recommendations (accessed October 7, 2026)
- American Diabetes Association Professional Practice Committee. 5. Facilitating Positive Health Behaviors and Well-being to Improve Health Outcomes: Standards of Care in Diabetes—2026. Diabetes Care 2026;49(Suppl 1):S89–S131. https://doi.org/10.2337/dc26-S005 (accessed October 7, 2026)
- NHS. Gout. Page reviewed August 24, 2023. https://www.nhs.uk/conditions/gout/ (accessed October 7, 2026)
- T.C. İçişleri Bakanlığı. 112 Acil Çağrı Merkezi. 2026. https://www.112.gov.tr/ (accessed October 7, 2026)
Frequently asked questions
How much weight can you lose on a water diet?
According to the 2023 review, weight fell by 2–10% in prolonged fasts of 5–20 days. However, about two-thirds of the loss was lean mass. According to TÜBER, weight lost quickly is regained in a short time.
Is a 3-day water fast harmful?
Human studies on the safety of short water fasts are few, and the risk varies from person to person. In people using diabetes drugs, diuretics or blood pressure drugs, even a short fast can be dangerous. TÜBER considers starvation diets below 200 calories risky. Consult your doctor before starting.
Does a water fast remove toxins?
No, there is no reliable evidence supporting this claim. The body regularly eliminates waste products through the liver and kidneys.
How many liters of water should I drink a day?
According to TÜBER 2022, the total fluid requirement is 2.5 liters a day for men and 2 liters for women. About 80% of this is met from beverages. If you have heart or kidney disease, determine your fluid intake with your doctor.
Is intermittent fasting safer than a water fast?
In intermittent fasting, food is eaten every day or on most days of the week. According to ADA 2026, intermittent fasting produces weight loss similar to continuous calorie restriction. Still, people using diabetes drugs, pregnant women and children need a doctor's approval.
