OMAD (One Meal a Day) — Diets

Extended fasting protocol with a single daily meal, providing approximately 23 hours of fasting per day.

Overview

OMAD (One Meal a Day) is an extreme form of time-restricted eating that confines all daily caloric intake to a single meal within approximately a 1-hour eating window. While less studied than 16:8 IF in formal RCTs, observational and mechanistic data suggest enhanced autophagy activation, deeper ketosis, and greater insulin sensitivity improvements compared to less restrictive TRE protocols. However, adherence is challenging, and risks of inadequate nutrient intake are higher. Studies suggest potential benefits for body composition but with concerns about meal timing effects on circadian metabolism.

Indications

Aggressive weight loss
Enhanced autophagy activation
Simplified meal planning
Metabolic flexibility training

Mechanism of Action

23 hours of fasting maximizes hepatic glycogen depletion and sustained ketone production

Dosing

Compound	Dose	Frequency	Notes
OMAD	Full daily calories in 1-hour window	Daily	Typically consumed at lunch or dinner; ensure nutrient density

Evidence Grade

GRADE C

Safety & Contraindications

Difficult to meet micronutrient and protein requirements in a single meal
May promote binge-eating behavior in susceptible individuals
Risk of hypoglycemia, especially with diabetes medications
Not suitable for athletes with high energy demands
May impair social eating and quality of life