You’re hungry. Your stomach is growling like a lawnmower, and the clock says it's only 11:00 AM. You've decided to try only eating once a day because someone on a podcast said it would turn you into a cognitive powerhouse with the body of an Olympic swimmer. But now, staring at a lukewarm cup of black coffee, you’re wondering if this is actually a health breakthrough or just a socially acceptable way to starve yourself.
Honestly? It's a bit of both.
The One Meal a Day diet, or OMAD, isn’t some new-age fad cooked up in a Silicon Valley basement. It’s a literal interpretation of Intermittent Fasting (IF), specifically the 23:1 protocol. You fast for 23 hours and cram your entire daily caloric needs into a single sixty-minute window. It sounds extreme. It is extreme. Yet, millions of people swear by it for weight loss, mental clarity, and the sheer simplicity of never having to think about Tupperware or meal prep during the workday.
The Science of Going Without
When you stop eating for 23 hours, things happen inside your cells that don't happen when you're snacking on almonds every two hours. It's called autophagy. The word literally means "self-eating." Nobel Prize winner Yoshinori Ohsumi brought this to the mainstream; it’s a process where your cells identify old, junked-up proteins and recycle them. It’s like a biological spring cleaning. If you’re constantly feeding, your body stays in "growth mode," driven by insulin. When you stop, you flip the switch to "repair mode."
Insulin is the big player here. Every time you eat, insulin spikes. This hormone tells your body to store fat. By only eating once a day, you keep insulin levels low for the vast majority of the 24-hour cycle. This forces your body to tap into its own fat stores—essentially your "pantry"—for energy.
But here is where people mess up.
They think OMAD is a free pass to eat a 3,000-calorie mountain of fast food at 6:00 PM. It’s not. If you spend your one hour eating inflammatory oils and refined sugars, you’re basically negating the cellular benefits of the previous 23 hours. You'll feel like garbage. Your blood sugar will skyrocket, then crash, leaving you shaky and irritable the next morning.
What Your Liver is Doing While You Wait
Your liver stores glucose in the form of glycogen. This is your "easy access" energy. It usually takes about 12 to 16 hours of fasting to deplete these stores. Once they're gone, your body looks for a new fuel source. This is ketosis. Even if you aren't on a "Keto Diet," by the 20th hour of an OMAD fast, you are likely producing ketones.
Ketones are a much "cleaner" fuel for the brain than glucose. That’s why people report that weird, almost buzzy sense of focus in the late afternoon. You aren't "hangry" anymore; you're dialed in. It's an evolutionary adaptation. Our ancestors needed to be sharpest when they were hungry so they could actually find food. If we became sluggish and stupid every time we missed a meal, humans would have gone extinct 100,000 years ago.
The Reality of Weight Loss
Most people come to OMAD because they want the scale to move. It works. Fast.
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But why?
Is it magic? No. It’s mostly just a very effective way to create a calorie deficit. It is remarkably difficult for the average person to eat 2,500 calories of whole foods in a single hour. Try eating three chicken breasts, two sweet potatoes, a giant salad, and an avocado in 45 minutes. You’ll feel like you’re going to pop. Naturally, most OMAD practitioners end up eating 1,200 to 1,800 calories without even trying. That deficit is what drives the fat loss.
However, there’s a dark side.
If you do this every single day without a break, your metabolic rate might start to dip. Your body is smart. If it thinks food is permanently scarce, it will start turning down the "thermostat" to save energy. This is why some people hit a plateau after three months of only eating once a day. They’ve trained their body to survive on very little, and the moment they eat a "normal" three-meal day, they gain weight instantly.
Variability is key. Some experts, like Dr. Mindy Pelz, suggest that women especially need to be careful with OMAD due to hormonal fluctuations. Fasting too hard during certain phases of the menstrual cycle can spike cortisol and mess with progesterone. It’s not a one-size-fits-all hammer.
Social Life and the "Weirdo" Factor
Let’s talk about the stuff no one puts in the scientific journals: your social life.
Eating is a social glue. If you work a 9-to-5 and your "window" is at 7:00 PM, you’re the person sitting at the lunch meeting with nothing but a glass of water. It’s awkward. You’ll get asked if you’re okay. You’ll get tired of explaining what autophagy is to your aunt who thinks breakfast is the most important meal of the day (a slogan, by the way, popularized by cereal companies, not doctors).
Then there's the "binge" risk.
For people with a history of disordered eating, OMAD can be a slippery slope. It can turn into a cycle of "starve and stuff." You spend all day obsessing over that one hour, and when it finally arrives, you lose control. If you find yourself inhaling food so fast you don't even taste it, OMAD might be doing more harm than good for your relationship with nutrition.
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Common Myths and Flat-Out Lies
Myth 1: You’ll lose muscle immediately.
Actually, fasting increases Growth Hormone (GH). This is a muscle-sparing hormone. As long as you are hitting your protein targets during your meal and doing some form of resistance training, you aren't going to wither away. Look at Dr. Ted Niman’s work on Protein-to-Energy ratios; the quality of that one meal matters immensely for muscle retention.
Myth 2: You can drink "some" cream in your coffee.
Technically, if you're doing it for weight loss, a splash of cream won't kill you. But if you want the cellular cleanup (autophagy), you need to stay in a fasted state. Anything that triggers an insulin response—even a bit of stevia or milk—breaks the fast. Stick to black coffee, plain tea, and water.
Myth 3: It’s the same as anorexia.
Anorexia is a psychological disorder characterized by a distorted body image and a refusal to eat to maintain a healthy weight. OMAD is a structured timing of nutrient intake. The goal of OMAD is still to eat a healthy amount of calories, just in a compressed timeframe.
How to Actually Do This Without Failing
If you’ve never fasted before, don’t start with OMAD tomorrow. You will fail. You'll get a massive headache, you'll be miserable, and you’ll quit by 4:00 PM.
Start with 16:8. Eat between noon and 8:00 PM.
Do that for two weeks.
Once that’s easy, move to 18:6. Then 20:4. Eventually, you’ll find that "only eating once a day" happens naturally because you just aren't that hungry anymore. Your body gets better at switching between burning sugar and burning fat. This is "metabolic flexibility."
When you finally sit down for that one meal, prioritize protein. Aim for at least 1 gram of protein per pound of ideal body weight. If you should weigh 160 lbs, try to get close to that in protein. It sounds like a lot because it is. But protein is what keeps you satiated enough to make it through the next 23 hours. Add some fiber (greens) and healthy fats (olive oil, nuts) to slow down digestion.
Electrolytes: The "Secret" to No Headaches
The reason most people feel like trash during a fast isn't actually hunger. It's salt.
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When insulin levels drop, your kidneys flush out sodium. If you’re just drinking plain water all day, you’re diluting your remaining electrolytes. You’ll get "fasting flu"—headaches, muscle cramps, and fatigue. Put a pinch of high-quality sea salt in your water. Or use a sugar-free electrolyte powder. It’s a game-changer. You’ll feel your brain "turn back on" within ten minutes.
Is It Sustainable Long-Term?
For some, yes. There are people who have eaten once a day for decades. They love the time they save. They love the mental clarity. They love the fact that they can eat a huge, satisfying dinner and still stay lean.
For others, it’s a tool. Use it for a few weeks to break a weight loss plateau or to reset your gut health after a vacation of eating junk. Then go back to a more relaxed 16:8 or 14:10 schedule.
There is no rule saying you have to do this 365 days a year.
In fact, "cycling" your fasting is probably better for your metabolism anyway. It keeps the body guessing. Some days eat once. Some days eat twice. On Sundays, maybe have brunch with your family. The best diet is the one you don't want to quit after three weeks because it's making your life miserable.
Signs You Should Stop Immediately
Listen to your body. Not the "I want a donut" voice, but the "something is wrong" voice.
If you start losing hair, your nails become brittle, or you stop sleeping through the night, your body is under too much stress. Fasting is a hormetic stressor—like exercise. A little bit makes you stronger; too much breaks you. If your cortisol is constantly high because you’re starving yourself and working a high-stress job and doing HIIT workouts, your body will eventually rebel. Usually by holding onto belly fat and making you feel exhausted.
Actionable Steps for Beginners
- Phase into it: Don't jump from three meals plus snacks to OMAD overnight. Spend a week on 16:8 first.
- Hydrate with intention: Drink more water than you think you need, but always include electrolytes (sodium, magnesium, potassium).
- The "One Hour" Rule: Don't just eat for an hour; eat until you are genuinely full on nutrient-dense foods. If you're full in 45 minutes, stop. If it takes 75, that’s fine too.
- Prioritize Protein: It is the most important macro for maintaining muscle and bone density while fasting.
- Check your bloodwork: If you’re doing this long-term, monitor your thyroid (TSH, T3, T4) and your vitamin levels.
- Plan your meal: Don't leave it to chance. If you're starving at the end of a fast, you'll grab whatever is easiest. Have a high-quality meal ready to go.
Only eating once a day is a powerful tool, but it’s just that—a tool. It isn't a religion. Use it when it serves your goals, and be flexible enough to eat a breakfast taco when life calls for it.