OMAD (One Meal a Day): How It Works and What We Know

In 30 seconds

OMAD means eating all your food in one meal a day, leaving a fast of 20 hours or more. In a small trial, one meal a day without cutting calories raised hunger, blood pressure and cholesterol and worsened morning blood sugar control. It’s a strict pattern that isn’t for everyone.

• OMAD means one meal a day; in the trial cited here, the meal was eaten between 5 and 9 p.m.
• That makes OMAD-as-tested close to a 20:4 schedule with a single meal in the window.
• Eating the same calories in one meal raised hunger, blood pressure and total, LDL and HDL cholesterol in 15 normal-weight adults, and fat mass fell.
• Morning fasting blood sugar was higher and glucose tolerance was worse; the change reversed after the diet.

What is OMAD?

OMAD stands for one meal a day. You eat everything in a single meal and fast for the rest of the day, which makes it one of the strictest forms of time-restricted eating. In the trial cited here, the meal was eaten in the early evening, leaving a fast of at least 20 hours.

In a randomized crossover trial, healthy normal-weight adults spent 8 weeks eating all the calories they needed to maintain weight in one meal a day, eaten between 5 and 9 p.m. after 2 initial weeks on two meals a day, which created a fast of at least 20 hours a day, and 8 weeks eating three meals a day.Source 11

So OMAD as it was tested sits very close to a 20:4 schedule: about 4 hours to eat, but with one meal instead of several.

What did the OMAD trial find?

The trial changed meal timing without cutting calories, so it can’t tell you whether OMAD helps with weight loss. The glucose results come from the same 15 people, published separately.

Compared with three meals a day, one meal a day significantly increased hunger, reduced fat mass, and raised blood pressure and total, LDL and HDL cholesterol, while body weight stayed within 2 kg.Source 11

In the same 15 participants, one meal a day led to higher morning fasting glucose and worse morning glucose tolerance with a delayed insulin response; the change was reversible.Source 22

Fifteen adults completed two 8-week periods, and 28.6% of those who started withdrew. Participants were healthy and normal-weight, calories weren't restricted, and it says nothing about OMAD over months or years.Source 11Source 22

Is OMAD better for weight loss?

There’s no evidence here that it is. No trial cited in this guide tested OMAD for weight loss or compared it with gentler schedules or daily calorie cutting. If you want to try fasting, how to start intermittent fasting begins with a gentler window.

Who should avoid OMAD?

Frequently asked questions

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• 20:4 Intermittent Fasting: How It Works

  20:4 intermittent fasting means about 20 hours of fasting and a 4-hour eating window. See a sample day, what trials found and when a gentler schedule wins.

• Intermittent Fasting Schedule: Common Options Compared

  Compare intermittent fasting schedules: 12:12, 14:10, 16:8, 18:6, 20:4 and 5:2. Trials found similar average effects, so pick one you can keep.

• 18:6 Intermittent Fasting: How It Works

  18:6 intermittent fasting means about 18 hours of fasting and a 6-hour eating window. See a sample day, what trials found and whether to go longer.

• Who Should Not Do Intermittent Fasting Without Advice?

  Who should not do intermittent fasting without advice? Diabetes medicines, pregnancy and eating disorders need care; few data on children or over-60s.

• Does Intermittent Fasting Affect Insulin?

  Small trials and a 2025 network meta-analysis show fasting changes glucose and insulin only a little, mostly in short studies.

Next steps

• Find a gentle starting point

  Three quick steps to explore a simple routine, with safety before schedules. This is not a medical assessment.

• When does my fast end?

  See the time remaining and an educational timeline. Hours on a clock are not a measurement of your body.

• Take the fasting quiz

  A few questions about your day, then a gentle place to start.

• Intermittent fasting protocols

  Compare the common schedules side by side.

Frequently asked questions

What is OMAD intermittent fasting?

One meal a day: you eat all your food in a single meal and fast for the rest of the day. It's a strict form of time-restricted eating; the trial cited here used a 5 to 9 p.m. window.Source 11

Is OMAD the same as 20:4?

Close. In the trial, the one meal was eaten within 4 hours, the same window as 20:4, but as a single meal rather than several.Source 11

Is OMAD healthy?

It hasn't been shown to be. In a small trial without calorie cuts, one meal a day raised hunger, blood pressure and total, LDL and HDL cholesterol and worsened morning blood sugar control, although fat mass fell.Source 11Source 22

Can you lose weight with OMAD?

No trial cited here tested OMAD for weight loss. In the trial, people ate enough to keep their weight, which stayed within 2 kg, although fat mass fell.Source 11

Sources

1. 1

   A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adultsKim S Stote et al. Elsevier BV, April 1, 2007.DOI: 10.1093/ajcn/85.4.981 · PMID: 17413096Human randomized trial

2. 2

   Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and womenOlga Carlson et al. Elsevier BV, December 1, 2007.DOI: 10.1016/j.metabol.2007.07.018 · PMID: 17998028Human randomized trial

3. 3

   Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance

4. 4

   Calorie restriction and fasting diets: What do we know?National Institute on Aging. National Institute on Aging, August 14, 2018.Official guidance

5. 5

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance

6. 6

   Low blood sugar (hypoglycaemia)NHS. NHS, August 3, 2023.Official guidance