Therapeutic Fasting: What It Is, How It Works and What the Science Says

Therapeutic fasting has been used as a health tool for centuries — from Hippocrates' fasting cures to modern Buchinger clinics in Europe. But it's not a diet. It's not for quick weight loss. It's a medical protocol that, when done correctly and under supervision, activates deep biological mechanisms: autophagy (cellular cleanup), immune system reset, inflammaging reduction, and tissue regeneration.

This post is a complete guide on what therapeutic fasting is, how it works at the cellular level, what the science says (with papers, not empty promises), contraindications, and how we apply it at Progevita within the Detox Reset Path program.

What is therapeutic fasting?

Therapeutic fasting is the voluntary and supervised abstinence from solid food for a determined period, maintaining minimal caloric intake (typically 200-500 kcal/day in the form of broths, juices, or teas), with the goal of activating cellular repair processes, reducing systemic inflammation, and resetting metabolism.

It's not the same as:

• Intermittent fasting (16:8, 14:10): daily eating windows. Intermittent fasting is a sustainable daily practice. Therapeutic fasting is a prolonged period (3-7 days) done sporadically.
• Pure water fasting: 0 calories, only water. It's more extreme and requires strict supervision. Therapeutic fasting includes broths and juices to provide minerals and facilitate adherence.
• Detox or juice diets: they're not fasting. If you consume 1200 kcal in juices, you're still eating. Therapeutic fasting involves severe caloric restriction (<500 kcal).

History: Therapeutic fasting has ancient medical roots (Hippocrates recommended it), but the modern tradition comes from the Buchinger method, developed by Dr. Otto Buchinger in Germany in 1920. The Buchinger Wilhelmi clinic (Marbella, Germany) has been applying supervised therapeutic fasting for 100 years with documented results.

Types of therapeutic fasting

There are several protocols, depending on duration and caloric intake:

1. Intermittent fasting (16:8, 18:6, 20:4)

Duration: daily windows.
Calories: ad libitum during eating window.
Goal: long-term sustainability, insulin sensitivity, weight control.
Is it therapeutic fasting? No. It's a daily nutritional strategy, not a metabolic reset.

2. Supervised prolonged fasting (3-7 days)

Duration: 3-7 consecutive days.
Calories: 200-500 kcal/day (broths, vegetable juices, teas).
Goal: activate deep autophagy, ketosis, immune system reset.
Is it therapeutic fasting? Yes. This is the classic model we apply at Progevita.

3. Modified Buchinger fasting

Duration: 5-10 days.
Calories: ~250 kcal/day (fruit juice in the morning, vegetable broth at noon and evening, teas).
Goal: gentle metabolic reset with minimal nutritional support.
Is it therapeutic fasting? Yes. European tradition with clinical evidence accumulated over decades.

4. Fasting-Mimicking Diet (FMD)

Duration: 5 days.
Calories: Day 1: ~1100 kcal; Days 2-5: ~800 kcal (specific macros: low protein, high fat).
Goal: mimic fasting effects without completely fasting. Designed by Valter Longo (USC).
Is it therapeutic fasting? Technically not fasting, but activates similar mechanisms (autophagy, ketosis).

5. Pure water fasting

Duration: 3-14 days.
Calories: 0 kcal (water only).
Goal: maximum autophagy, deep ketosis.
Is it therapeutic fasting? Yes, but it's the most extreme. Should only be done under strict medical supervision due to risk of hypoglycemia, electrolyte imbalances, and refeeding syndrome.

At Progevita we use the supervised prolonged fasting model (3-5 days, 250-400 kcal/day), with vegetable broths, teas, and low-sugar vegetable juices. It's a balance between biological effectiveness, safety, and adherence.

Biological mechanisms: what happens in your body during fasting

Therapeutic fasting isn't magic. It's biology. When you stop eating for more than 12-16 hours, your body enters a different metabolic mode. Here's what happens, step by step:

1. Metabolic switch: from glucose to ketones (ketosis)

Normally: Your body uses glucose (from carbohydrates) as primary fuel.

During prolonged fasting (>12-24h):

• Glycogen stores (stored glucose) are depleted.
• The liver starts producing ketone bodies from stored fat.
• Brain and tissues switch from glucose to ketones as energy source.

Result: You enter metabolic ketosis. Ketones aren't just fuel — they also have anti-inflammatory and neuroprotective effects.

Key paper: De Cabo & Mattson, New England Journal of Medicine (2019) — "Effects of Intermittent Fasting on Health, Aging, and Disease"
→ Explains how the metabolic switch (from glucose to ketones) reduces oxidative stress, improves stress resistance, and increases longevity in animal models.

2. Autophagy activation: cellular cleanup

What is autophagy? From Greek auto (self) and phagy (eating). It's the process by which cells self-digest damaged, old, or dysfunctional components (misfolded proteins, broken mitochondria, intracellular pathogens) and recycle them.

Why does it matter? With age, autophagy becomes less efficient. "Cellular garbage" accumulates, dysfunctional mitochondria, and protein aggregates — this contributes to aging and neurodegenerative diseases (Alzheimer's, Parkinson's).

Fasting activates autophagy because:

• It lowers mTOR (mechanistic Target of Rapamycin) signaling, a protein that promotes cell growth when nutrients are available. High mTOR = growth. Low mTOR = cleanup.
• It increases AMPK (AMP-activated protein kinase) activity, an enzyme activated when cellular energy is low. High AMPK = autophagy ON.

Key paper: Yoshinori Ohsumi won the 2016 Nobel Prize in Medicine for discovering autophagy mechanisms.
→ He identified ATG (autophagy-related genes) in yeast, later confirmed in humans.

Key paper 2: De Cabo & Mattson (NEJM, 2019):
> "During fasting, the AMP/ATP ratio increases, AMPK is activated, mTOR is inhibited → stimulation of autophagy and cellular repair."

3. mTOR inhibition and sirtuin activation

mTOR (mechanistic Target of Rapamycin): Protein that promotes growth, protein synthesis, and cell division when nutrients are available.

• High mTOR: growth, proliferation (good when you're young, problematic when you're older).
• Low mTOR: autophagy, repair, longevity.

Fasting lowers mTOR, which:

• Activates autophagy (cellular cleanup).
• Reduces systemic inflammation.
• Improves insulin sensitivity.

Sirtuins (SIRT1-7): NAD+-dependent proteins that regulate metabolism, inflammation, DNA repair, and longevity. They're called "longevity proteins" because their activation is associated with increased lifespan across multiple species (C. elegans, mice).

Fasting activates sirtuins because:

• It increases the NAD+/NADH ratio (fasting improves NAD+ availability, essential sirtuin cofactor).
• SIRT1 improves mitochondrial function, reduces inflammation, and protects against age-related diseases.

Key paper: Sinclair & Guarente, Nature (2006) — "Unlocking the Secrets of Longevity Genes"
→ Showed that sirtuins mediate the longevity effects of caloric restriction.

Progevita connection: The NAD+ therapy we offer activates the same pathways as fasting — reinforcing cellular cleanup and mitochondrial repair effects. You can also read more about sirtuins and longevity.

4. Inflammaging reduction (chronic aging inflammation)

Inflammaging: Low-grade chronic inflammation that increases with age. It's one of the 12 hallmarks of aging (López-Otín et al., Cell 2023).

Fasting reduces inflammaging because:

• It lowers pro-inflammatory cytokine levels (IL-6, TNF-α, CRP).
• It reduces the number of senescent cells that secrete SASP (senescence-associated secretory phenotype) — inflammatory molecules.
• It improves immune system function (immune cell regeneration).

Key paper: Jordan et al., Cell (2019) — "Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool"
→ Showed that fasting reduces circulating inflammatory monocytes, decreasing systemic inflammation.

Progevita connection: We combine therapeutic fasting with therapeutic plasma exchange (plasmapheresis) to remove inflammatory proteins, microplastics, and heavy metals from blood — a deep system reset.

5. Stem cell regeneration and immune system reset

Key finding from Valter Longo (USC): Prolonged fasting (>48-72h) regenerates the immune system by forcing hematopoietic stem cells (in bone marrow) to produce new immune cells.

Mechanism:
During fasting, the body "recycles" old and dysfunctional immune cells (immune cell autophagy). When reintroducing food, there's a regeneration boom — stem cells produce new, younger, and more functional immune cells.

Key paper: Cheng et al., Cell Stem Cell (2014) — "Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic Stem Cell-Based Regeneration and Reverse Immunosuppression"
→ Demonstrated that prolonged fasting in mice and humans regenerates immune system cells, reversing immunosuppression.

Key paper 2: Longo et al., Cell Metabolism (2015) — "Fasting-Mimicking Diet and Markers of Aging, Diabetes, Cancer, and Cardiovascular Disease"
→ Clinical trial showing that FMD cycles (5 days, every 1-3 months) improved biomarkers of aging, diabetes, and cardiovascular health.

6. Improved insulin sensitivity and glycemic control

Insulin resistance is one of the drivers of metabolic aging. It increases the risk of type 2 diabetes, obesity, and cardiovascular disease.

Fasting improves insulin sensitivity because:

• It empties glycogen stores (body uses stored fat instead of glucose).
• It lowers fasting insulin levels (when not eating, insulin drops dramatically).
• It activates AMPK, which improves glucose uptake without needing as much insulin.

Key paper: Sutton et al., Cell Metabolism (2018) — "Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress"
→ Showed that intermittent fasting (early eating window) improves insulin sensitivity in pre-diabetic men.

Benefits of therapeutic fasting (evidence-backed)

Summarizing the above, these are the documented benefits of therapeutic fasting:

1. Autophagy activation and cellular cleanup

Evidence: Ohsumi (Nobel 2016), De Cabo & Mattson (NEJM 2019).

2. Systemic inflammation reduction (inflammaging)

Evidence: Jordan et al. (Cell 2019), Buchinger clinic studies (>5000 documented patients).

3. Improved insulin sensitivity and glycemic control

Evidence: Sutton et al. (Cell Metabolism 2018), Longo et al. (Cell Metabolism 2015).

4. Visceral fat loss (not just weight)

Fasting reduces abdominal (visceral) fat, the most dangerous for metabolic and cardiovascular health.

5. Immune system reset

Evidence: Cheng et al. (Cell Stem Cell 2014) — hematopoietic stem cell regeneration.

6. Neuroprotection and mental clarity

Ketones are neuroprotective. Studies show fasting improves cognitive function, memory, and reduces Alzheimer's risk.
Evidence: Mattson et al. (Lancet Neurology 2019).

7. Increased longevity (in animal models)

Caloric restriction and fasting extend life in yeast, worms, flies, and mice.
Evidence: López-Otín et al. (Cell 2023) — caloric restriction is one of the most robust interventions to extend lifespan.

8. Improved cardiovascular markers

Reduction in blood pressure, LDL cholesterol, triglycerides.
Evidence: Wilhelmi de Toledo et al. (PLOS ONE 2019) — study in 1422 patients at Buchinger clinic showed improvements in BP, lipids, and glucose.

What to expect during a 5-day fast: day by day

Day 1 — Adaptation:

• Moderate hunger (still have glycogen).
• Stable energy, but you may feel anxiety about not eating (it's psychological, not physiological).
• Recommendation: stay busy, hydrate, drink teas.

Day 2 — Metabolic transition:

• Glycogen depletes → body starts producing ketones.
• Intense hunger at first, then decreases (ketones suppress appetite).
• Possible effects: slight headache, fatigue (it's temporary — body is switching fuel).
• Recommendation: rest, gentle walking, avoid intense exercise.

Day 3 — Established ketosis:

• You're in metabolic ketosis.
• Mental clarity: many people report improved concentration, clearer thoughts.
• Almost no hunger (ketones do the work).
• Stable energy (though lower than normal).

Day 4-5 — Deep autophagy:

• Autophagy in full process.
• Feeling of lightness, emotional reset.
• Some report more vivid dreams.
• Hydration key (drink 2-3L water/day).

Day 6 (refeeding):

• Breaking the fast gradually is critical to avoid refeeding syndrome.
• Start with diluted fruit juices, broths, then soft fruits, then light meals.
• Don't overeat — digestive system has been resting.

Contraindications: who should NOT fast

Therapeutic fasting is safe under medical supervision, but it's NOT for everyone.

Absolute contraindications:

• Type 1 diabetes: risk of ketoacidosis.
• Pregnancy and breastfeeding: you need nutrients for the baby.
• Eating disorders (ED): fasting can trigger relapses.
• BMI <18.5 or malnutrition: no fat reserves to burn.
• Severe kidney or liver failure: body can't handle ketosis.
• Under 18 years: still developing.

Relative contraindications (require medical evaluation):

• Type 2 diabetes with medication: risk of hypoglycemia. Need to adjust insulin/metformin doses.
• Hypertension with medication: BP can drop significantly. Adjust drugs.
• Gout history: fasting can temporarily increase uric acid.
• Desired pregnancy soon: fasting can temporarily affect menstrual cycle.

Importance of medical supervision:
Therapeutic fasting is NOT "stop eating and that's it". It requires:

• Pre-fasting diagnostics: complete blood work, medical evaluation.
• Monitoring during fasting: daily measurements of glucose, ketones, blood pressure, vital signs.
• Guided refeeding: refeeding protocol to avoid refeeding syndrome (dangerous electrolyte imbalance).
• Support treatments: hydrotherapy, electrolyte serums, ozone therapy to facilitate detox.

Most serious risk: Refeeding syndrome — when you reintroduce food after prolonged fasting without supervision, there can be sudden drop in phosphate, potassium, magnesium → arrhythmias, seizures, multi-organ failure. It's rare, but real. That's why Progevita monitors electrolytes before, during, and after fasting.

How we do therapeutic fasting at Progevita: the Detox Reset Path program

At Progevita, therapeutic fasting is NOT a mystical retreat or a fad diet. It's a medically supervised metabolic reset, integrated into the Detox Reset Path program.

The program includes:

1. Pre-fasting medical evaluation

• Consultation with longevity specialist physician before arrival.
• Complete blood work (liver function, kidney, glucose, insulin, electrolytes).
• Body composition evaluation (bioimpedance) to measure visceral fat, muscle mass.

2. Structured fasting protocol (4 nights)

• Day 1: Light transition meal (vegetables, no animal protein).
• Days 2-4: Modified fasting (~250-400 kcal/day) with vegetable broths, low-sugar juices, teas.
• Day 5: Gradual refeeding (juices, fruits, light meals).

3. Daily monitoring

• Glucose, ketone measurements (blood or breath).
• Blood pressure, heart rate.
• Symptom evaluation (fatigue, dizziness, mental clarity).

4. Complementary treatments

• Ozone therapy: improves cellular oxygenation, facilitates detox.
• IV serums: electrolytes, vitamins, NAD+ (under medical recommendation).
• Colon hydrotherapy (optional): to eliminate accumulated toxins.
• Ice baths + sauna: enhance autophagy, improve circulation.

5. Post-fasting education and habits

• Workshops on anti-inflammatory nutrition.
• Food reintroduction plan.
• Sustainable intermittent fasting protocol for home (16:8 or 14:10).
• 2 post-stay follow-up sessions to evaluate biomarkers and adjust plan.

Progevita differentiator vs other fasting retreats:

• Real medical supervision (not just wellness coaches).
• Advanced diagnostics (before/after biomarkers, not just weight).
• Comprehensive treatments (ozone therapy, NAD+, optional plasmapheresis).
• Clinical environment, not a luxury hotel without doctors.

Therapeutic fasting vs intermittent fasting: which to choose?

Intermittent fasting (16:8, 14:10):

• Goal: long-term sustainability, weight control, insulin sensitivity.
• Frequency: daily or almost daily.
• Duration: 12-16h fasting windows.
• Autophagy: moderate (activated from 12-16h).
• For whom: any healthy person wanting to optimize metabolic health.

Prolonged therapeutic fasting (3-7 days):

• Goal: deep metabolic reset, maximum autophagy, immune regeneration.
• Frequency: sporadic (1-4 times per year).
• Duration: 3-7 consecutive days.
• Autophagy: deep (>48h).
• For whom: people seeking a more intense reset, under medical supervision.

Progevita recommendation:
Combine both. Daily intermittent fasting (16:8) as habitual practice + prolonged therapeutic fasting 1-2 times per year as deep reset.

Conclusion: fasting as a tool, not as a goal

Therapeutic fasting is not a panacea. It doesn't magically cure diseases. But it's a powerful tool when used correctly:

• Activates autophagy (cellular cleanup) — Nobel 2016 mechanism.
• Reduces systemic inflammation (inflammaging).
• Improves insulin sensitivity and glycemic control.
• Regenerates immune system (Longo papers, USC).
• Improves mental clarity and cognitive function.

But it requires:

• Medical supervision.
• Before/after diagnostics (not just subjective feelings).
• Gradual refeeding (avoid refeeding syndrome).
• Integration with sustainable habits (not fast and then go back to eating junk).

At Progevita, therapeutic fasting is part of the Detox Reset Path program — a complete metabolic reset with medical supervision, biomarkers, advanced treatments, and education so benefits last months, not days.

If you're considering therapeutic fasting, don't do it alone. Do it right.

Request information about the Detox Reset Path program here: Contact Progevita

Scientific references

1. De Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine. 2019;381:2541-2551.
2. Ohsumi Y. Mechanisms for Autophagy. Nobel Prize in Physiology or Medicine. 2016.
3. Cheng CW et al. Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic Stem Cell-Based Regeneration. Cell Stem Cell. 2014;14(6):810-823.
4. Longo VD et al. Fasting-Mimicking Diet and Markers of Aging, Diabetes, Cancer, and Cardiovascular Disease. Cell Metabolism. 2015;22(1):86-99.
5. López-Otín C et al. Hallmarks of Aging: An Expanding Universe. Cell. 2023;186(2):243-278.
6. Wilhelmi de Toledo F et al. Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLOS ONE. 2019;14(1):e0209353.
7. Sinclair DA, Guarente L. Unlocking the Secrets of Longevity Genes. Nature. 2006;444(7122):868-874.
8. Mattson MP et al. Impact of intermittent fasting on health and disease processes. Lancet Neurology. 2019;18(1):75-87.
9. Jordan S et al. Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell. 2019;178(5):1102-1114.

This article is for informational purposes and does not replace individual medical consultation.

Want to know if the Detox Reset Path program is right for you? Talk to our medical team and design a personalized protocol at Balneario de Cofrentes, Valencia.