Eating once a day for weight loss: Why your results might vary

You’re hungry. Probably. If you’ve been scrolling through social media lately, you’ve definitely seen the acronym OMAD. It stands for One Meal a Day, and honestly, it’s exactly what it sounds like. You fast for 23 hours. You eat for one. It sounds like a crash diet from the 90s, but it’s actually the most extreme version of intermittent fasting. People swear by it. They say it’s the secret to "biohacking" their way to a leaner body without counting every single calorie in a salad.

But does eating once a day for weight loss actually work for everyone?

The short answer is yes. If you eat less, you lose weight. Physics doesn’t care about your feelings. However, the long answer is way more complicated because your hormones, your sleep, and your stress levels are all sitting in the background waiting to mess things up.

The science of the 23:1 window

When you stop eating, your body doesn't just sit there. It shifts. Usually, your body runs on glucose—basically sugar from the carbs you ate earlier. But after about 12 to 14 hours of not eating, those glycogen stores start to run low. This is where things get interesting. Your insulin levels drop. Low insulin is the "green light" for your body to start tapping into stored body fat for energy.

Dr. Jason Fung, a nephrologist and author of The Obesity Code, has spent years talking about this. He argues that obesity isn't just about calories; it’s a hormonal issue. By eating once a day for weight loss, you are essentially keeping your insulin levels low for the vast majority of the day. This theoretically prevents insulin resistance.

There’s also autophagy. This is a word that gets thrown around a lot in the "longevity" community. It’s basically cellular cleanup. Your body starts recycling old, damaged cell components. While most of the data on autophagy comes from mice or yeast, human studies on fasting suggest that longer windows of calorie restriction might trigger these cellular repair processes. It’s like a deep clean for your insides.

But let’s be real. Most people aren't doing OMAD for cellular repair. They want to fit into their old jeans.

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Why OMAD feels like a magic trick (at first)

It’s simple math. It is genuinely hard to eat 2,500 calories in a single hour unless you are actively trying to win a hot dog eating contest. Most people naturally end up in a calorie deficit because their stomach can only hold so much volume at once. You feel full. You feel "stuffed," even.

I’ve seen people eat a massive ribeye, a baked potato, and a giant salad, and still come in under their daily calorie needs. That’s the appeal. You get to eat a "normal" or even "large" meal and still see the scale move down the next morning. It removes the "nibbling" problem. No more mindless handfuls of almonds or "just one" cracker. Those little things add up to hundreds of calories by 3:00 PM. On OMAD, those don't exist.

The metabolic "Wall" and the cortisol trap

It isn't all sunshine and ribeyes. There is a dark side to eating once a day for weight loss that people often ignore until they hit a massive plateau.

Stress is the big one.

Fasting is a stressor. For most healthy people, it’s a good stressor (hormesis). But if you are already stressed at work, sleeping four hours a night, and drinking six cups of black coffee to stay awake, OMAD might be the thing that breaks you. When you fast for a long time, your body releases cortisol. Cortisol is the "fight or flight" hormone. In small bursts, it helps mobilize fat. In chronic amounts? It causes water retention and can actually make you hold onto belly fat.

If you notice that you’re losing weight everywhere except your midsection, or if you’re suddenly "skinny-fat," your cortisol might be the culprit.

Women and the hormonal tightrope

We have to talk about biology. Men often thrive on OMAD because their hormones are relatively linear. Women? Not so much. The female body is highly sensitive to signs of "famine."

If the brain (specifically the hypothalamus) senses that food is scarce, it might downregulate reproductive hormones. This can lead to irregular periods, hair thinning, or even thyroid issues. Some experts, like Dr. Mindy Pelz, suggest that women should vary their fasting windows based on their menstrual cycle rather than sticking to a strict one-meal-a-day schedule every single day of the month.

Basically, don't force it if your body is screaming at you.

What should that one meal actually look like?

You can’t just eat a box of doughnuts and call it a day. Well, you can, but you’ll feel like garbage.

If you’re only eating once, that meal has to be a nutritional powerhouse. You need protein. A lot of it. Aiming for at least 0.8 to 1 gram of protein per pound of ideal body weight is a good target. Why? Because protein keeps you full and protects your muscles. If you lose 20 pounds but 10 of it is muscle, your metabolism will tank, and you’ll gain the weight back the second you eat a sandwich at lunch.

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• Protein first: Chicken, beef, eggs, tofu, or fish.
• Fiber second: Massive amounts of greens. Fiber is what keeps your digestion moving when you aren't eating regularly.
• Healthy fats: Avocado, olive oil, or nuts. These are essential for hormone production.

Avoid the "junk-food OMAD" trap. Just because you have the "calorie room" for a fast-food meal doesn't mean your mitochondria will be happy about it. High-sugar meals during your one-hour window will cause a massive insulin spike, which might lead to a "sugar crash" later, making the next 23 hours of fasting feel like torture.

The psychological game

OMAD changes your relationship with hunger. You start to realize that hunger comes in waves. It isn't a linear buildup that gets worse and worse until you faint. It’s a hormone called ghrelin. Ghrelin spikes at the times you usually eat. If you always eat at noon, you’ll be hungry at noon. If you skip it, the hunger usually fades after about 45 minutes.

But for some, this can trigger disordered eating patterns. If you find yourself obsessing over that one meal all day, or if you feel a "binge" sensation when you finally sit down to eat, this isn't the strategy for you. There is a very fine line between "disciplined fasting" and "restrict-binge cycles."

Be honest with yourself. If you’re white-knuckling it every single day, it’s not sustainable.

Common pitfalls that ruin your progress

1. The "Creamer" Mistake: You think a little splash of oat milk in your coffee won't hurt. It does. It breaks the fast. It raises insulin. It stops the fat-burning state. Stick to black coffee, plain tea, or water.
2. Under-eating: This sounds counterintuitive for weight loss, but if you only eat 800 calories in your one meal, your body will eventually slow down your basal metabolic rate (BMR). You'll feel cold, tired, and your hair might start falling out.
3. The Weekend Blowout: Doing OMAD Monday through Friday and then eating everything in sight on Saturday and Sunday. This usually results in net-zero progress.

How to actually start (and keep) eating once a day for weight loss

Don't just wake up tomorrow and decide you aren't eating until 7:00 PM. You'll fail.

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Start with a 16:8 window (16 hours fasting, 8 hours eating). Do that for a week. Then move to 18:6. Then 20:4. Let your body's enzymes and hormones catch up to the change. This is called metabolic flexibility—the ability of your body to switch between burning sugar and burning fat. It takes time to build that "muscle."

Actionable steps for success:

• Hydrate with electrolytes: When you fast, your kidneys flush out sodium. If you get a headache, it’s probably not hunger; it’s dehydration. Put a pinch of high-quality sea salt in your water.
• Time your meal wisely: Some people love "Dinner OMAD" because they can eat with their family. Others prefer "Late Lunch OMAD" because eating too close to bed can ruin sleep quality. Experiment.
• Prioritize Sleep: If you don't sleep, your hunger hormones (ghrelin) will be 20% higher the next day. You will fail your fast if you are exhausted.
• Listen to the "Hard" Signals: A growling stomach is fine. Dizziness, heart palpitations, or feeling "blacked out" are not. If you feel legitimately ill, eat something. The fast can always start again tomorrow.
• Track more than the scale: Take photos. Measure your waist. Sometimes the scale stays the same while your body composition shifts because you're losing fat and retaining water or building muscle.

Eating once a day for weight loss is a tool, not a religion. It works because it simplifies your life and controls your insulin. But if it makes you miserable, social-isolated, or physically ill, it’s okay to just eat two meals a day. The best diet is the one you can actually follow for more than three weeks.