This article presents an international consensus on the terminology of fasting, including terms such as fasting, intermittent fasting, time-restricted eating, long-term and short-term fasting, and fasting-mimicking diets. The consensus was developed through a Delphi methodology involving 38 experts from five continents, who participated in five online surveys and a live conference. The key findings include: - **Fasting**: Defined as voluntary abstinence from some or all foods or beverages for preventive, therapeutic, religious, cultural, or other reasons. - **Modified Fasting**: Refers to fasting regimens that limit energy intake to typically up to 25% of energy needs. - **Fluid-Only Fasting**: Involves consuming only beverages during a fasting period. - **Alternate-Day Fasting**: Involves alternating days of fasting with non-fasting days. - **Short-Term Fasting (STF)**: Lasts 2-3 days. - **Prolonged Fasting (PF/LTF)**: Lasts ≥4 consecutive days. - **Intermittent Fasting (IF)**: Involves repetitive fasting periods lasting up to 48 hours. - **Time-Restricted Eating (TRE)**: Involves a fasting window of at least 14 hours per day. - **Fasting-Mimicking Diet (FMD)**: Allows for a higher caloric intake (≥50% of energy needs) on some "fasting" days. The consensus aims to standardize terminology in clinical fasting research and practice, facilitating communication and cross-referencing in the field. The study highlights the need for further research to refine and expand the definitions, particularly in areas where there is limited scientific data.This article presents an international consensus on the terminology of fasting, including terms such as fasting, intermittent fasting, time-restricted eating, long-term and short-term fasting, and fasting-mimicking diets. The consensus was developed through a Delphi methodology involving 38 experts from five continents, who participated in five online surveys and a live conference. The key findings include: - **Fasting**: Defined as voluntary abstinence from some or all foods or beverages for preventive, therapeutic, religious, cultural, or other reasons. - **Modified Fasting**: Refers to fasting regimens that limit energy intake to typically up to 25% of energy needs. - **Fluid-Only Fasting**: Involves consuming only beverages during a fasting period. - **Alternate-Day Fasting**: Involves alternating days of fasting with non-fasting days. - **Short-Term Fasting (STF)**: Lasts 2-3 days. - **Prolonged Fasting (PF/LTF)**: Lasts ≥4 consecutive days. - **Intermittent Fasting (IF)**: Involves repetitive fasting periods lasting up to 48 hours. - **Time-Restricted Eating (TRE)**: Involves a fasting window of at least 14 hours per day. - **Fasting-Mimicking Diet (FMD)**: Allows for a higher caloric intake (≥50% of energy needs) on some "fasting" days. The consensus aims to standardize terminology in clinical fasting research and practice, facilitating communication and cross-referencing in the field. The study highlights the need for further research to refine and expand the definitions, particularly in areas where there is limited scientific data.