What Is OMAD? The One Meal a Day Diet Explained for Over-50s
OMAD is simple to describe and harder to do well. Here is what it actually means, how it compares with other fasting patterns, what the research does and doesn't show, and the questions worth asking before you try it after 50.
OMAD in one sentence
OMAD stands for One Meal A Day. You eat everything you need for the day in a single sitting, usually within about an hour, and don't eat for the rest of the day. Because that works out at roughly 23 hours of fasting and one hour of eating, you will often see it written as 23:1.
That's the whole idea. There is no list of banned foods and no points to count. The rules are about when you eat, not what. That simplicity is a big part of the appeal, and it's also where people over 50 can come unstuck, because one meal has to carry a whole day's nutrition.
Check with your GP first if this applies to you
If you take regular medication, or have diabetes, kidney disease, blood pressure problems or a history of disordered eating, speak to your GP before trying OMAD. This guide is general information for healthy adults, not medical advice.
Where OMAD fits among fasting styles
OMAD is a form of intermittent fasting, sometimes called time-restricted eating. Most people who fast use a much shorter daily fast. OMAD sits at the far end of the range:
| Pattern | Fasting | Eating window |
|---|---|---|
| 12:12 | 12 hours | 12 hours (for example, 7am to 7pm) |
| 16:8 | 16 hours | 8 hours |
| 18:6 | 18 hours | 6 hours |
| 20:4 | 20 hours | 4 hours |
| OMAD (23:1) | About 23 hours | About 1 hour, one meal |
The jump from 16:8 to OMAD is bigger than it looks on paper. With 16:8 you can still fit two meals in. With OMAD, one plate has to provide all your protein, fibre, vitamins and minerals for the day. Our guide OMAD vs 16:8 goes through which suits who.
What a day on OMAD looks like
Most people pick a fixed time for their meal and stick to it, often late afternoon or early evening so it fits around work and family. For the rest of the day, people following OMAD generally stick to water and other drinks without calories. Keeping up your fluids matters, and so do salts such as sodium, potassium and magnesium, which our electrolytes guide covers.
The meal itself should be a proper meal, built around protein, with vegetables, fibre and healthy fats. It isn't a licence to eat anything at all because it's the only meal. Our guides What to Eat in Your One Meal and What Time Should You Eat Your One Meal? go into the detail.
Why people try it
OMAD's appeal is mostly practical: fewer decisions about food, less time spent cooking, and a simple structure that can make it easier to eat less overall if you're trying to lose weight. For some people those are real advantages. But it's worth being clear that the reasons people like OMAD are mostly about convenience. They aren't proof that it is healthier than eating the same food across two or three meals.
What the research actually shows
There is very little research on eating one meal a day, and almost none in people over 50. The study most often quoted was carried out by the US Department of Agriculture and the US National Institute on Aging and published in 2007. Fifteen healthy, normal-weight adults aged roughly 40 to 50 ate either one meal a day, within about four hours in the early evening, or three meals a day, for eight weeks each. Their calories were kept the same, so it wasn't a weight-loss diet.
On one meal a day, the volunteers:
- Felt noticeably hungrier
- Lost some body fat
- Had higher blood pressure
- Had higher total and LDL (“bad”) cholesterol, along with higher HDL (“good”) cholesterol
A further analysis of the same group found that on one meal a day they had higher morning blood sugar and a slower response to insulin.
It's a small, short study, in younger people than our readers, with a longer eating window than true OMAD. It doesn't prove OMAD is harmful. But it is the closest direct evidence there is, and it's a good reason to keep an eye on your blood pressure, cholesterol and blood sugar if you try OMAD, especially if any of them are already a concern.
What changes after 50
The things that can go wrong on OMAD tend to matter more as you get older:
- Muscle. We lose muscle gradually with age, and one meal makes it harder to eat enough protein. See How Much Protein Do You Need on OMAD After 50?
- Medication. Some tablets need to be taken with food or at set times. See OMAD and Your Medication.
- Fluids and salts. Dizziness and headaches on a long fast are often down to fluids and electrolytes.
- Gallstones. Long daily fasts and fast weight loss can be linked to gallstones. See Does OMAD Increase Your Risk of Gallstones?
Who should not do OMAD
Know Diabetes, reporting the British Dietetic Association's verdict on intermittent fasting, says never to delay or skip meals if you are pregnant, have had or are prone to eating disorders, or have diabetes. People with diabetes are also advised to tell their diabetes team before changing their eating plan, because medication may need adjusting.
On top of that, we'd strongly suggest talking to your GP first if you take medication for blood pressure, have a kidney condition, or have any condition where missing meals has caused problems before. Our guide Is OMAD Safe After 50? has the full checklist.
How to start, if it's right for you
- Don't go straight from three meals to one. Build up through 12:12 and 16:8 first, as explained in Easing Into OMAD.
- Pick a regular meal time that fits your medication and your life
- Build the meal around protein, then vegetables and fibre
- Drink water through the day and keep an eye on your salts
- Track more than the scales: energy, sleep, strength, and blood pressure if you can
- Review after a few weeks, and widen your eating window if you feel worse rather than better
The bottom line
OMAD means eating once a day and fasting for roughly 23 hours. It's simple, and some people find it suits them, but the research behind it is thin and the one direct study raised questions about blood pressure, cholesterol and blood sugar. After 50, it's worth approaching with a plan: ease in, protect your muscle, sort out your medication timing, and check with your GP first if any of the warnings above apply to you.
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- Stote et al. (2007), American Journal of Clinical Nutrition: A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults
- US Department of Agriculture, Agricultural Research Service: Researchers look at how frequency of meals may affect health (2008)
- Know Diabetes: Intermittent fasting (including the British Dietetic Association verdict)