The evidence is thin. In a small trial, eating once a day raised blood pressure and cholesterol compared with three meals of the same calories. Do not try OMAD without medical advice if you are pregnant, breastfeeding or under 18, or take insulin or sulfonylureas. OMAD is something we advise against after an eating disorder, or when you are underweight.

Is OMAD better than 16:8 for weight loss?

Only if it leads you to eat less in total. When calories are matched, trials of daily eating windows found about the same weight loss as ordinary calorie cutting. The best schedule for weight loss is the one that keeps your weekly calories lower.

How much protein do I need in one meal on OMAD?

All of it for the day. The adult minimum is 0.8 g per kg of body weight, so a 70 kg adult needs at least 56 g in that one meal. People who exercise are advised 1.4 to 2.0 g per kg, which is 98 to 140 g for the same person.

Can I drink coffee during the 23-hour fast?

Yes. A cup of black coffee has about 2 calories. Under about 50 calories makes little difference to a weight-loss fast, by a popular rule of thumb that has no official status. Milk, sugar and syrups add up quickly.

OMAD Intermittent Fasting: How One Meal a Day Works

OMAD intermittent fasting puts a whole day’s food into one meal, usually eaten within an hour. The other 23 hours or so have no calories. OMAD has few rules. The hard part is that one meal has to supply all of your protein and energy for the day. Planning that meal matters more than the clock.

What OMAD means, and how it compares with 22:2 and 2MAD

OMAD stands for “one meal a day”. The same schedule is written 23:1 or 23/1, meaning 23 hours of fasting and a 1-hour eating window. OMAD is a type of intermittent fasting, so “OMAD or intermittent fasting” is a choice between OMAD and a wider daily window. Our 16:8 vs 18:6 vs OMAD comparison covers that choice for anyone deciding between schedules.

Two close relatives come up often. Intermittent fasting 22 hours a day, written 22:2 or 22/2, leaves a 2-hour window. 2MAD, sometimes written 2OMAD, means two meals a day. With a 4- to 8-hour window, 2MAD sits close to 20:4 or 16:8.

Schedule	Hours fasting	Eating window	Example window if your last bite is at 7 pm
OMAD (23:1)	23	1 hour	6 pm to 7 pm
22:2	22	2 hours	5 pm to 7 pm
20:4	20	4 hours	3 pm to 7 pm
2MAD at 16:8	16	8 hours	11 am to 7 pm

The fasting calculator has OMAD as its longest daily preset. Enter when you last ate and it shows when the next meal falls, with a live countdown.

What happens during a 23-hour fast

For the first few hours you are still digesting the meal, and glucose is the main fuel. From about hour 4, insulin falls and the liver starts drawing on glycogen, the sugar it keeps in reserve, to hold blood sugar level. As that reserve runs low, the body burns more fat and starts making ketones.

That last step, the metabolic switch, happens somewhere between 12 and 36 hours in human studies. The timing depends on what you last ate and how active you are. So a 23-hour fast reaches the switch for some people on some days, and not for others. All the hours here are approximate and vary between people.

Is OMAD intermittent fasting good for weight loss?

One small trial has tested intermittent fasting with one meal a day directly. Healthy, normal-weight middle-aged adults ate the same calories as one meal or as three meals a day, each for 8 weeks. On one meal a day they were hungrier and lost a little fat mass. Their blood pressure and their total, LDL and HDL cholesterol also rose. The calories were set to keep weight steady, and weight stayed within 2 kg. The evidence on OMAD itself is early, from one small, short trial.

For weight loss, the stronger evidence comes from other fasting schedules. A 12-month trial followed 139 adults with obesity. People who ate within an 8-hour window and also cut calories lost 8.0 kg. Those who only cut calories lost 6.3 kg. The difference was not significant. A 2025 review of 99 trials found intermittent fasting and everyday calorie cutting give similar results overall. The review’s authors called this “some indication”, so the evidence is moderate. When calories are equal, the timing makes little difference.

So OMAD vs intermittent fasting for weight loss comes down to how much you eat in total. A short eating window can cut calories without counting. In an 8-week trial, people eating only in a 4-hour window ate about 550 kcal a day less than before. That is an average, and some people make up the difference at the one meal they eat. Our intermittent fasting for weight loss guide goes through the numbers.

How much protein one meal has to hold

Protein is where OMAD gets difficult, because the whole day’s need lands on one plate. Here is a worked example for an adult who weighs 70 kg (154 lb):

Who	Protein per kg a day	Total for one meal at 70 kg
Adult minimum	0.8 g	56 g
People who exercise	1.4 to 2.0 g	98 to 140 g
Aged 65 and over	1.0 to 1.2 g (1.2 g or more if active)	70 to 84 g

The body stats panel on the home page does this sum for you. Choose one meal and it shows that meal’s calories and protein, with a note when the amount is a lot to eat at once.

Energy is the other half. The 2013 US obesity guideline’s lowest usual diet targets are 1,200 kcal a day for women and 1,500 kcal for men. This site’s calorie calculators never show a target below those. Reaching 1,500 kcal in one meal takes a large plate. Fats pack a lot of energy into a small amount. A tablespoon (15 ml) of olive oil is about 120 kcal, and a 30 g handful of almonds about 170.

How to do intermittent fasting one meal a day

If you want to try OMAD, these steps keep the risk lower:

Build up first. Start from a schedule you already manage, such as 16:8, and add an hour or two at a time. The schedule chooser never suggests OMAD, even for people who eat one meal already, and stops at 18:6.
Fix the meal time. Pick a time that works on most days and set it in the calculator. Then add the eating window to your calendar with one click.
Plan the plate around protein. Put the protein on the plate first, then vegetables, then starch and fat to reach your energy target.
Keep the fast clean. Water, black coffee (about 2 kcal a cup) and plain tea suit the fasting hours. Under about 50 calories makes little difference to a weight-loss fast, by a popular rule of thumb that has no official status.
Check how you feel. In the trial above, hunger rose on one meal a day. If hunger leads to a binge, or you feel dizzy or faint, go back to a wider window.

Some people use OMAD on a few days and a 16:8 window on the rest, which spreads the protein load over the week.

Is OMAD safe, and who should skip it?

Do not try OMAD without medical advice if you:

are trying to conceive, or are pregnant (losing weight on purpose is not advised in pregnancy)
are breastfeeding
are under 18
have, or have had, an eating disorder (avoid OMAD then, in our advice)
are underweight (again, we advise against OMAD), frail, or recovering from illness or surgery
have type 1 diabetes, or use insulin or a sulfonylurea (both can make blood sugar drop too low)
need to take a medicine with food

If you take blood-pressure medicine and feel dizzy or faint while fasting, stop the fast and speak to your doctor. Some people stretch OMAD to 24 hours or more between meals. Check with a doctor before any gap between meals goes over 24 hours.

Stop and get urgent help for chest pain, fainting, confusion, a racing or irregular heartbeat, repeated vomiting or changes in your vision. In an emergency, call the local emergency number. It is 112 in the EU and 999 in the UK, while the US and Canada use 911. If food or fasting is causing you distress, talk to a doctor; findahelpline.com has a free helpline for your country.

To see where a one-meal day would sit in your own week, open the fasting calculator, choose OMAD and enter the time you last ate.