Lifestyle

Fasting

Voluntary abstention from food for a defined period. It is not a diet or a weight-loss fad, but a metabolic switch that activates ketosis and autophagy. This is the central node that groups all fasting modalities.

In practice

Choose one modality and stick with it: adherence matters more than the exact protocol. Start with the overnight window (≥13 h) or 16:8 and increase intensity only if it agrees with you.

Precautions

Contraindicated in pregnancy and breastfeeding, diabetes treated with insulin or hypoglycemic drugs (risk of hypoglycemia), a history of eating disorders, and low body weight. In children and adolescents, only under medical supervision.

Fasting modalities

Intermittent fasting
Daily windows 16:8, 5:2. The most studied and accessible.Prolonged overnight fasting (≥13 h)
Extend the overnight fast to ≥13 h. The most sustainable option.Alternate-day fasting
Alternate days of normal eating with days of ≈500 kcal (ADF).48-hour fast
Two-day fast; activates autophagy more deeply.Weight-loss diets
Long fasts (3-5 days) applied to weight loss.Fasting-mimicking diet (FMD)
700-1,100 kcal/day, 5 days a month; replicates fasting with better adherence.Fasting cycles (alongside chemotherapy)
Short cycles around chemotherapy; oncology research.Exercise + intermittent fasting (combined)
Training fasted to enhance metabolic adaptation.

In depth

⏱ 3 min read

Fasting is one of the oldest metabolic interventions in human history and, paradoxically, one of the least understood today. All the modalities grouped here share the same underlying mechanism and differ mainly in the duration and frequency of the period without food.

From a biochemical standpoint, fasting operates through the so-called metabolic switch: with regular feeding the body burns glucose; when the fast extends between 12 and 36 hours—depending on glycogen stores and physical activity—the body shifts to beta-oxidation of fatty acids and to producing ketone bodies, mainly beta-hydroxybutyrate, which besides serving as fuel acts as an anti-inflammatory and neuroprotective signaling molecule.

The mTOR–AMPK–autophagy axis

The drop in nutrients reduces mTOR signaling (the main inhibitor of autophagy) and raises AMPK activity (the cellular energy sensor that stimulates it). The result is autophagy: the program by which the cell degrades and recycles misfolded proteins and damaged organelles. Deficient autophagy is associated with the protein aggregates characteristic of Alzheimer's disease, Parkinson's disease, and ALS, with greater susceptibility to cancer, and with diminished immunity.

The longer or deeper the fast (48-h fasts, FMD cycles), the more this pathway is activated; daily windows are gentler but easier to sustain over time, and in practice sustainability is what determines the real benefit.

How to choose a modality

There is no universally superior modality: the choice should be based on individual adherence, goal, and medical context. For most people, an eating window of 8-10 hours or an overnight fast of at least 13 hours offers the best balance between benefit and sustainability. Valter Longo's fasting-mimicking diet (FMD) replicates the effects of prolonged fasting with much greater adherence, and fasting cycles alongside chemotherapy are an oncology research line still under evaluation.

Information, not medical advice. Scientific evidence reflects the quality of the studies.