Introduction
Fasting, the voluntary abstinence from food or other comforts, has been practiced for centuries for various reasons, including spiritual, ethical, and health-related purposes. In recent years, there has been growing interest in fasting as a weight loss strategy. This article delves into the science behind a 40-day fast for weight loss, exploring its potential benefits, risks, and impact on the body.
Understanding Fasting and Its Physiological Effects
Throughout history, humans have adapted to periods of food scarcity. Most individuals possess sufficient fat stores to survive several weeks without food. During fasting, the body undergoes several metabolic changes.
Metabolic Adaptations During Fasting
Glycogen stores are limited, with liver glycogen being depleted after 24-36 hours without food. Muscle glycogen, the primary substrate during moderate to high-intensity exercise, decreases by only 20-30% after three days of fasting.
Fasting elicits well-established changes in plasma metabolites, including decreased plasma glucose and increased plasma fatty acids (FA) and ketones. A recent study indicated that the plasma concentration of unsaturated FAs increased much more compared to saturated FAs after ten days of fasting.
Protein Degradation and Muscle Strength
During fasting, protein degradation becomes the main source of amino acids for gluconeogenesis. While it's uncertain whether this protein degradation includes contractile proteins, studies have shown that grip strength is well-preserved during the first two weeks of fasting, followed by a decline.
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One study reported preservation of maximal strength in leg muscle, despite a significant loss of lean mass. This suggests that humans maintain their capacity for physical abilities well during periods of severe food shortage. However, high-intensity endurance capacity may decrease despite unchanged expression of mitochondrial enzymes in skeletal muscle.
The 40-Day Fast: Examining the Evidence
While the concept of a 40-day fast has biblical roots, its effects on the human body and mind are less documented, especially in the long term.
Case Study: A 50-Day Fast
One case study followed a 34-year-old obese male who undertook a 50-day fast with the goal of losing weight. During this time, he consumed only tea, coffee, water, and a daily multivitamin. The patient experienced a severe and linear loss of body mass throughout the 50 days.
Interestingly, the patient showed surprising resilience to the effects of fasting on activity levels and physical function. However, plasma samples suggested early impairment of liver function, and perturbations to cardiovascular dynamics were also noted. One month after resuming feeding, his body weight was maintained.
Considerations for Extreme Fasting
This case study highlights that the starting mass is a key variable in survival during extreme fasting. The patient started fasting while obese and ended his fast when his anthropometric variables were within the targeted ranges for the general population.
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However, it's important to note that survival in starvation is ultimately governed by the calories available to maintain metabolic function. Organ-specific effects of starvation, such as loss of liver and gut size and function, have been noted in animal models after only four to six days. In the case study, elevated direct bilirubin suggested reduced liver filtration, which remained elevated 30 days after breaking the fast. Hypertension was also an unexpected finding in this case.
Alternate-Day Fasting: A Less Extreme Approach
Alternate day fasting (ADF) involves alternating between a "fast day" with 25% energy intake and a "feed day" with ad libitum eating. Studies in obese individuals have shown that ADF is effective for weight loss and visceral fat mass loss. It may also aid in the retention of lean mass and improve cardiovascular health markers.
ADF in Non-Obese Individuals
A study examined the effect of ADF on body weight and coronary heart disease risk in non-obese subjects (BMI 20-29.9 kg/m2). After 12 weeks, the ADF group experienced a significant decrease in body weight and fat mass compared to the control group. They also saw improvements in triacylglycerol concentrations, LDL particle size, CRP, adiponectin, and leptin.
This study suggests that ADF can be an effective strategy for moderate weight loss in normal weight and overweight individuals, with potential cardio-protective effects.
Long-Term Fasting: A Controlled Experiment
To assess the physiological safety and effects of long-term fasting, a 34-day experiment was conducted, including 21 days of complete fasting (CF) with mineral water only, followed by gradual refeeding.
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Impact on Body Weight and Composition
The volunteers experienced an average body weight loss of 10.00 ± 1.66 kg (14.96%±1.55%) at the end of the 21-day fasting period. The rate of weight loss was rapid in the early stages of fasting but stabilized later on. During the refeeding phase, the weight gain was relatively rapid, highlighting the need for strict dietary control during recovery.
The study also found that fat mass significantly decreased, while lean mass markedly declined during the fasting period.
Metabolic Changes During Fasting
Resting metabolic rate (RMR) was assessed by indirect calorimetry. RMR showed no changes on day five of fasting compared to before the prolonged fasting period. Resting RER declined, and fat oxidation increased its contribution to total energy turnover, while carbohydrate contribution fell. Blood pressure was lower after five days of fasting, and resting capillary lactate was higher.
During a maximal fat oxidation test, RER was lower at every incremental step after the fasting period, indicating increased fat oxidation rates and decreased carbohydrate oxidation. The maximal fat oxidation rate increased significantly.
Metabolic Response to Exercise
Plasma glucose decreased after six days of fasting but increased after the maximal fat oxidation test and VO2peak test. Plasma β-Hydroxybutyrate was low before the fasting period but increased significantly after six days of fasting.
Metabolomics analysis revealed that the plasma FA concentration nearly quadrupled in response to prolonged fasting. The most abundant FAs, 16:0 (palmitic acid) and 18:1 (oleic acid), showed divergent responses, with 18:1 increasing more significantly.
Potential Risks and Considerations
While fasting can offer potential benefits, it's crucial to be aware of the risks involved, especially with prolonged or extreme fasting.
Side Effects and Risks
Common side effects of prolonged fasts include headaches, insomnia, and hunger. Additionally, prolonged fasts may lead to a loss of lean mass, which is the opposite of what typically happens during weight loss.
Other potential risks include:
- Impairment of liver function
- Cardiovascular issues
- Dysregulated autonomic regulation of blood pressure
- Nutrient deficiencies
- Dehydration
- Electrolyte imbalances
Contraindications
Fasting is not suitable for everyone. Certain individuals should never fast without professional supervision, including:
- People with a history of eating disorders
- Pregnant or breastfeeding women
- Individuals with certain medical conditions, such as diabetes, kidney disease, or liver disease
- Those taking certain medications
Safe Fasting Practices
If you're considering a 40-day fast or any prolonged fasting regimen, it's essential to prioritize safety and consult with a healthcare professional.
Planning and Preparation
Before starting a fast, spend time planning it out and determining a prayer focus and vision for the set time. It's also important to transition well by eating smaller meals before and avoiding a large meal right before the fast.
Hydration and Electrolytes
During the fast, drink plenty of water to stay hydrated. Consider supplementing with electrolytes to maintain balance.
Moderate Exercise
Engage in moderate exercise, such as walking, but avoid high-intensity activities.
Breaking the Fast
Breaking the fast is just as important as the fasting period itself. Reintroduce food gradually, starting with liquids and easily digestible foods.