Dietitian
"Water fasting is a diet model that carries serious health risks, leading to muscle loss, metabolic disorders, electrolyte imbalances, and negative effects on gut health, while also slowing down metabolism in the long term."
Title:
| What is Water Fasting?
| An Overview of the Water Fasting Process
| Effects of Zero-Calorie Intake
| Caloric Restriction and Gut Microbiota
| Caloric Restriction and Intestinal Motility
| Low Protein Intake and Risks
| Vitamin-Mineral Deficiencies and Risks
| Metabolic Slowdown and Appetite Perception
What is Water Fasting?
Long-term fasting can be defined as consciously consuming very little or no food for several days to weeks. Water fasting can be considered one of the types of long-term fasting. Water fasting is a type of fasting in which only water is consumed. During this process, a person drinks only water for a specific period without any calorie intake. Water fasting is often preferred for detoxification and weight loss purposes. However, it carries many health risks.
An Overview of the Water Fasting Process
Water fasting, which has recently gained popularity, has no professional or scientific basis. Beginning a water fast on one’s own is akin to voluntarily walking towards the edge of a cliff. For the body to function properly, for organs to work, and for movement to be sustained, energy is needed. This energy is obtained daily from food. However, nutrition should not be evaluated solely in terms of energy. Through nutrition, a person also receives the necessary daily intake of carbohydrates, proteins, fats, vitamins, and minerals.
In cases of inadequate nutrition, the body first uses carbohydrate stores in the muscles to meet its energy needs. This consumption is referred to as "muscle loss." Muscle loss also leads to water loss, which is why individuals may mistakenly believe they are losing weight on the scale. Later, the body attempts to compensate for the energy deficit by utilizing fat stores. However, prolonged reliance on fat rather than carbohydrates for energy has many disadvantages. Byproducts that can damage the brain barrier are released, potentially leading to ketoacidotic coma. Once fat stores are depleted, the body begins consuming its protein reserves, which essentially means the breakdown of organs. This process can ultimately lead to death.
The aforementioned steps only address the body's need for energy. A "so-called diet" like water fasting, which involves consuming no food, can lead to severe vitamin and mineral deficiencies. The absence of essential vitamins and minerals has such critical effects that they can be observed quickly and severely. In individuals who frequently attempt such diets, the long-term risks include diabetes, cardiovascular diseases, inflammatory diseases, eating disorders, and intestinal diseases. In studies conducted to examine the effects of water fasting, healthy volunteers were closely monitored by medical professionals due to the life-threatening risks involved. Water fasting has not been tested on individuals with existing health conditions due to its high potential for exacerbating illnesses.
Among the observed effects of water fasting are increased blood concentrations of uric acid* and creatinine**, reduced kidney function, and other severe health complications. Additionally, since proteins begin to be used as an energy source, muscle loss progressively increases.
*Uric acid is a parameter used to assess kidney function and as a marker of gout disease.
**Creatinine is frequently used as an indicator of kidney damage, muscle loss, and tissue breakdown.
Ketosis is a metabolic consequence that develops from the early days of fasting. Over time, the individual transitions into metabolic acidosis, where blood pH balance is disrupted, causing the blood to become acidic. Metabolic acidosis initiates a harmful process that encourages calcium release from bones. Therefore, one of the negative effects of water fasting is bone mineral loss and degradation.
Effects of Zero-Calorie Intake
Some diabetic individuals choose water fasting in hopes of regulating blood sugar and alleviating diabetes symptoms. However, in healthy individuals who undergo this diet, reductions in fasting glucose, fasting insulin, insulin resistance, and glycated hemoglobin (HbA1c) levels have been observed. In contrast, these factors remain unchanged in individuals with type 1 or type 2 diabetes. Such a diet is administered in a hospital setting under the supervision of healthcare professionals for the first four hours of a 24-hour intervention for individuals hospitalized due to diabetic coma. This supervised protocol should not be confused with "water fasting." In normoglycemic individuals, experiencing such reductions poses a significant risk for future health complications.
Long-term fasting can further lower blood pressure in individuals with hypotension, leading to fainting, falls, fatigue, weakness, and even heart attacks. Additionally, metabolic acidosis can cause side effects such as vomiting, headaches, insomnia, confusion, and excessive hunger. Despite its name, water fasting paradoxically causes significant water loss from the body.
Studies have been conducted on healthy individuals, but long-term water fasting poses severe risks for those with underlying health conditions (e.g., diabetes, kidney, or liver failure). In diabetics, it can lead to severe hypoglycemia, while in healthy individuals, it can cause electrolyte imbalances and reduced blood volume.
Caloric Restriction and Gut Microbiota
A study found that water fasting leads to a reduction in beneficial bacterial species in the gut microbiota. This decrease can negatively affect gut health. During water fasting, gut microbiota density declines, disrupting bacterial balance. The reduction in certain bacterial species may cause constipation or other health issues post-diet. Additionally, studies have shown that the gut mucus layer thins during fasting, which could weaken the intestinal barrier over time.
Caloric Restriction and Intestinal Motility
When food intake stops, the digestive system enters a "resting" state, slowing bowel movements. In water fasting, the intestines become less active, and the digestive process stalls. Reduced bowel motility can lead to constipation. Additionally, prolonged water fasting prompts the body to alter hormone and neurotransmitter levels that regulate intestinal movement. Gut flora and digestive enzymes are also affected. If fasting continues for an extended period, these changes become more pronounced, and it may take time for the digestive system to return to normal function.
Low Protein Intake and Risks
Studies indicate that prolonged fasting (5 to 20 days) significantly increases circulating ketones and causes mild to moderate weight loss of 2-10%. Approximately two-thirds of the weight loss is lean mass, while one-third is fat mass. Excessive lean mass loss suggests that prolonged fasting accelerates muscle protein breakdown, which is concerning.
- During fasting, the body uses not only fat tissue but also protein for energy, leading to muscle loss.
- Elevated levels of branched-chain amino acids (BCAAs) indicate that the body is breaking down protein tissues for energy. Over time, this makes it difficult to maintain muscle mass.
- Muscle loss can accelerate cardiovascular diseases, negatively affecting heart and vascular health.
Postmenopausal women, elderly individuals, those with metabolic disorders, and athletes who attempt water fasting for weight management risk significant skeletal muscle loss.
Vitamin-Mineral Deficiencies and Risks
During water fasting, individuals are advised to consume 2-3 liters of mineralized water daily. These minerals are highly absorbable and sometimes better absorbed than those from food, making them an important advantage during fasting. However, insufficient water intake and nutrient deficiencies can lead to sodium and potassium loss, increasing the risk of reduced blood volume.
Studies have shown changes in electrolyte levels, particularly significant drops in sodium. This can increase the risk of dehydration and electrolyte imbalances. Blood pressure instability in hypertensive individuals can pose life-threatening risks. In individuals with osteoporosis or in developmental stages, reduced bone calcium levels may cause severe skeletal damage.
Metabolic Slowdown and Appetite Perception
A study observed a 20.3% decrease in basal metabolic rate following an 8-day water fast. This suggests that post-diet, an individual will have a slower metabolism, making weight management more challenging. If post-fasting dietary and exercise habits are not carefully managed, weight gain can occur. Additionally, individuals who abstain from food for an extended period may develop altered emotional and psychological relationships with food. Post-water fasting, individuals may experience sudden appetite surges, rapid weight gain, digestive issues, fatigue, and reduced vitality.
In summary, water fasting:
- Lacks medical justification even under supervision,
- Can weaken the immune system, cause muscle loss, and negatively affect gut health,
- Poses life-threatening risks for individuals with chronic conditions such as diabetes, hypertension, or kidney failure
Dai, Z. et al. Analysis of physiological and biochemical changes and metabolic shifts during 21-Day fasting hypometabolism. Scientific Reports (2024).
Damluji AA. et al. Sarcopenia and Cardiovascular Diseases. Circulation (2023).
Ezpeleta , M. et al. Efficiency and safety of prolonged Water diet: a narrative Human Review trials . Nutrition Reviews (2024).
Laurens C. et al. Is muscle and protein loss relevant in long term fasting in healthy men? A prospective Trial on Physician adaptations . Journal of Cachexia , Sarcopenia and Muscle (2021).
McCarthy D. and Berg A. Weight Loss Strategies and the Risk of Skeletal Muscle Mass Loss. Nutrients, (2021).
Mesnage R. et al. Changes in human gut microbiota composition are linked to the energy metabolic switch during 10 days of Buchinger fasting . Journal of Nutrition Science (2019).
Obembe, AO et al Effect of fasting on intestinal motility and transit in albino wistar rats. Trends Med Res, (2015).
Ogłodek , E. and Pilis , W. Is Water-Only Fasting Safe? Global Advances in Health and Medicine (2021).
