Is Fasting a Medicine or a Poison? Analyzing the 10-Day Fasting Debate on Social Media with the Latest Evidence

1. Fasting Trend Resurges: "Water Only Challenge" Spreads in Japan

In recent years, the "water fasting" method has rapidly gained popularity as a diet trend, thanks to wellness influencers and celebrities. The hashtag "#WaterFastingChallenge" has over 140,000 mentions on X (formerly Twitter) and nearly 100,000 posts on Instagram. However, a recent study published in June 2025 has cast a shadow over this trend.infomoney.com.br

2. Overview of the Study: Tracking 20 People on "Water Only" for 10 Days

Professor Luigi Fontana and his team at the Charles Perkins Centre, University of Sydney, conducted a medically supervised 10-day complete fast on 20 participants (11 women and 9 men, average age 41.3 years, BMI=27.4). The subjects consumed only electrolyte water, with daily blood tests and body composition measurements.infomoney.com.brinnovatopia.jp

2-1. Changes in Weight and Body Composition

• Weight: Average -7.7%

• Waist circumference: -6%

• Body fat percentage: -5.1 points
  The research team notes, "These numbers are faster than intermittent fasting (IF), but there may be a loss of muscle mass."innovatopia.jp

2-2. Subjective Symptoms

From the fourth day onward, 65% of participants reported headaches, 40% reported insomnia, and 30% reported orthostatic hypotension.infomoney.com.br

2-3. Blood Biomarkers

• CRP: +120%

• IL-8: +85%

• β-Amyloid: -14%
  The unexpected surge in inflammation markers led researchers to state, "Rather than being anti-inflammatory, there's a risk of 'pro-inflammatory' effects."innovatopia.jp

3. Reactions on SNS ── Divided Opinions, the Shifting Line of "Self-Responsibility"

Example of a Positive Experience── Yoga instructor Elly writes, "No hunger on the 8th day of fasting, my skin has transformed."note.com
Critical Perspective── President Online strongly warns with "Death case from 32-day water fasting."president.jp
Focus of the Debateis converging on and .

4. Experts Discuss the "Safety Line"

Professor Fontana suggests "Fasting over 48 hours should be under medical supervision." Japanese clinical nutritionists add, "Women should also consider impacts on menstrual cycles and bone density."innovatopia.jpsndj-web.jp

4-1. Recommended Alternatives

• 16/8 Hour Fasting: Previous studies have shown a decrease in inflammation markers.spc.jst.go.jp

• 5:2 Fasting: Restrict to 500-600 kcal for 2 days a week, low risk of dehydration.

5. Mechanism of Inflammasome Activation (See Diagram)

In the late fasting phase (days 8-10), adipose tissue macrophages may release IL-1β and IL-18, potentially inducing a systemic CRP increase. The decrease in β-amyloid is presumed to be due to elevated ketone bodies altering the APP degradation pathway.

6. Checklist for Japanese Practitioners

1. Define Objectives: Weight Loss / Metabolic Improvement / Gut Health? The optimal fasting method varies by objective.

2. Consult Healthcare Providers: Essential if there is a history of cardiovascular disease, diabetes, or eating disorders.

3. Electrolyte Supplementation: Avoid deficiencies in Na, K, Mg

4. Refeeding Phase: Start with low-GI soft solid foods (e.g., miso soup + rice porridge)

5. Mental Care: Anticipate sleep disturbances and emotional instability during fasting, and establish a support system

7. Future Research Topics

• Expansion and Diversification of Sample Size (including gender ratio and elderly)

• Long-term Prognosis of Inflammation Increase—Does CRP Normalize After Refeeding?

• Wearable-Linked Real-Time Inflammation Tracking Technology