OMAD: one meal a day

What is OMAD?

OMAD stands for one meal a day: 23 hours of fasting and a single meal within an hour. It's the shortest eating window of the daily plans in Fasting Tracker, and an advanced one. Many people use it a few days a week rather than every day.

What the evidence says

We haven't found a well-designed trial of OMAD itself among the studies behind Fasting Tracker's guides, so be wary of anyone who promises specific results. The closest evidence is the 4-hour window: adults with obesity lost about 3% of their weight in 8 weeks, mainly because they ate less ¹. A single meal may cut calories further, but it also makes it harder to eat enough protein, fibre and nutrients.

Can one meal give you enough protein?

More than you might think. The old idea that your body can only use about 30 g of protein at a time came from short studies of fast-digesting protein on its own. When researchers followed labelled protein after a workout, a 100 g dose kept building muscle for more than 12 hours, and very little was simply burned off ². Still, spreading protein over several meals worked a little better than one or two large servings ³, which is one reason daily OMAD isn't ideal if you're trying to build muscle.

What your body may do in 23 hours

1. 0 hBlood Sugar RisingYour body is digesting your last meal and using that energy. Insulin is elevated.
2. 4 hBlood Sugar FallingBlood sugar settles back to normal and insulin starts to drop.
3. 12 hFuel SwitchYour liver's glycogen is getting low, so your body starts turning to fat for fuel.
4. 16 hFat BurningYour body starts burning stored fat for energy. Stay hydrated!

By 23 hours, fat is a major fuel and ketones are rising; Ketosis typically begins around 24 hours ⁴. Hunger tends to come in waves around your old meal times rather than building steadily ⁵.

Doing OMAD well

Sources

1. Cienfuegos S, Gabel K, Kalam F, et al. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metab. 2020;32(3):366-378.e3. doi.org/10.1016/j.cmet.2020.06.018
2. Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023;4(12):101324. doi.org/10.1016/j.xcrm.2023.101324
3. Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013;591(9):2319-31. doi.org/10.1113/jphysiol.2012.244897
4. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-268. doi.org/10.1002/oby.22065
5. Natalucci G, Riedl S, Gleiss A, et al. Spontaneous 24-h ghrelin secretion pattern in fasting subjects: maintenance of a meal-related pattern. Eur J Endocrinol. 2005;152(6):845-50. doi.org/10.1530/eje.1.01919
6. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. Am J Clin Nutr. 2015;101(6):1320S-1329S. doi.org/10.3945/ajcn.114.084038
7. Sigler MH. The mechanism of the natriuresis of fasting. J Clin Invest. 1975;55(2):377-87. doi.org/10.1172/JCI107941
8. Blau JN, Kell CA, Sperling JM. Water-deprivation headache: a new headache with two variants. Headache. 2004;44(1):79-83. doi.org/10.1111/j.1526-4610.2004.04014.x
9. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi.org/10.3390/nu11040873