You’re sitting there at 7:00 PM on a Tuesday, staring at a plate of chicken that you can’t actually eat for another twenty hours. Your stomach is making noises that sound suspiciously like a heavy metal drum solo. This is the reality of the 24 hour fast once a week, a protocol often called One Meal a Day (OMAD) when it becomes a lifestyle, though most people just call it "the hardest day of my week."
Why do we do this to ourselves? Honestly, it’s because the science behind giving your digestive system a total break is becoming harder to ignore, even if the hunger pangs feel very, very real in the moment.
It’s not just about "starving" yourself.
When you stop eating for a full day, your body stops looking outward for fuel and starts looking inward. It’s like a spring cleaning for your cells. Researchers call this autophagy. It’s a fancy Greek word that basically means "self-eating," which sounds terrifying but is actually the holy grail of longevity. Dr. Yoshinori Ohsumi actually won a Nobel Prize in 2016 for his work on this. He showed that when cells are stressed by fasting, they start breaking down old, junk proteins and turning them into energy. It’s biological recycling.
What a 24 hour fast once a week does to your blood sugar
Let’s talk about insulin.
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Most of us are walking around with insulin levels that are way too high because we graze on snacks from 8:00 AM until we hit the pillow at night. Your pancreas never gets a day off. By implementing a 24 hour fast once a week, you force your insulin levels to drop off a cliff—in a good way.
This drop is the key to fat burning.
Think of insulin like a gatekeeper. When it’s high, the fat cells are locked shut. You can run on a treadmill until you’re blue in the face, but if your insulin is spiked from a sugary "pre-workout" drink, your body is going to burn that sugar instead of the fat stored on your hips. During a 24-hour stretch, your body eventually runs out of glycogen (stored sugar in your liver). Once that tank is empty, it has no choice. It has to burn fat.
It's efficient. It’s blunt. It works.
The mental game of the "Wall"
Around the 18-hour mark, things get weird.
This is what I call the Wall. You’ll probably feel a bit irritable, maybe a little "hangry," and you’ll start noticing every single fast-food commercial on TV. Your brain is screaming for glucose. But then, something interesting happens around hour 20 or 22. The hunger often just... vanishes.
This is partly due to ghrelin. Ghrelin is the hunger hormone, and it’s a bit of a creature of habit. It rises at the times you usually eat. If you always eat lunch at noon, ghrelin spikes at noon. If you ignore it, it actually goes back down. You aren't "getting hungrier and hungrier" until you pass out; you're just riding waves. Once you're over that hump, many people report a sense of mental clarity that’s almost like a caffeine buzz without the jitters. Your brain, sensing a lack of food, pivots into "hunter mode," amping up focus to help you find your next meal.
Except in 2026, your next meal is just in the fridge, and you're just waiting for the clock to hit 7:00 PM.
Is this actually safe for everyone?
Probably not.
Look, if you have a history of disordered eating, a 24-hour fast is a terrible idea. It can trigger a binge-restrict cycle that’s hard to break. Also, if you’re type 1 diabetic or pregnant, don't even think about it without a doctor hovering over you.
Real talk: women often respond differently to long fasts than men do.
Some studies suggest that extreme fasting can mess with the HPO axis (the connection between your brain and ovaries), potentially throwing off menstrual cycles if done too aggressively. For many women, a 24-hour fast once a week might be the upper limit of what's beneficial before the body starts sensing "starvation" and ramps up cortisol. Cortisol is the stress hormone, and too much of it leads to water retention and—ironically—belly fat.
You have to listen to your body. If you feel dizzy, shaky, or like you’re about to faint, eat something. It’s not a failure; it’s data.
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The "How-To" that nobody tells you
Most people mess this up by starting at the wrong time.
The easiest way to pull off a 24 hour fast once a week is the dinner-to-dinner method. You eat a solid, protein-rich dinner on Monday night. You go to sleep. You wake up Tuesday, skip breakfast (easy), skip lunch (getting harder), and then eat dinner again on Tuesday night.
You’ve technically gone 24 hours without food, but you slept through eight of them, and you still got to eat on both days.
Hydration is your only friend here.
Plain water. Black coffee. Green tea. No, "diet" soda doesn't count for the purists because the artificial sweeteners can still trigger an insulin response in some people. And for the love of everything, get some electrolytes. Take a pinch of sea salt and put it on your tongue or mix it in your water. A lot of the "fasting headache" people complain about is just sodium deficiency. When insulin drops, your kidneys dump sodium. If you don't replace it, you'll feel like garbage.
What happens when you finally eat?
This is the danger zone.
The biggest mistake people make with a 24 hour fast once a week is the "Reward Meal." You think, "I haven't eaten all day, so I deserve this entire pepperoni pizza and a liter of soda."
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If you do that, you just nuked all the hormonal benefits of the fast.
Your first meal back should be controlled. Start with something small—maybe a few nuts or a cup of bone broth—to wake up your digestion. Then, thirty minutes later, have a real meal. Focus on protein and fiber. If you blast your system with refined carbs immediately after a fast, your blood sugar will skyrocket, you'll get a massive insulin spike, and you'll likely feel bloated and exhausted an hour later.
Treat the refeed with as much respect as the fast itself.
The big picture on longevity
Dr. Valter Longo, a leading researcher in longevity at USC, has done extensive work on "fasting-mimicking" diets. While his specific protocol is different, the underlying principle is the same: periodic caloric deprivation is a biological necessity that we've removed from modern life.
Our ancestors didn't have Uber Eats. They had periods of forced fasting because the hunt failed or the berries weren't in season. Our bodies are literally designed to thrive under this occasional stress. It’s called hormesis—a beneficial stress that makes you stronger.
By doing a 24 hour fast once a week, you aren't just losing weight. You're potentially lowering systemic inflammation. You're giving your gut microbiome a chance to reset. You're reminding your body how to use its own fat stores for energy.
Moving forward with a protocol
If you want to try this, don't just jump into a 24-hour window if you're used to eating six times a day.
- Start with 16:8. Eat for 8 hours, fast for 16. Do that for a couple of weeks.
- Move to 20:4. This gets you used to the feeling of a "mostly empty" day.
- Pick your day. Most people find Tuesdays or Wednesdays easiest because they are busy with work. Weekends are tough because of social pressures and brunch invitations.
- Stock up on salt. Good quality sea salt or an electrolyte powder with zero sugar (like LMNT or similar) is a lifesaver.
- Plan your break-fast meal. Have it ready in the fridge so you don't make poor choices when the clock finally hits 24 hours.
Consistency beats intensity. Doing this once and then never again won't change your life. Doing it once a week for six months? That's where the magic happens. You’ll likely find that your relationship with food changes. You stop fearing hunger. You realize that "hunger" is often just boredom or thirst in disguise.
Focus on the electrolytes, keep the black coffee flowing, and remember that the first three times are the hardest. After that, your body adapts, and the 24-hour mark starts to feel like just another Tuesday.
Practical Next Steps
- Select your fasting window: Decide if you’ll go dinner-to-dinner or breakfast-to-breakfast.
- Clear the calendar: Choose a day with moderate work tasks but no high-intensity gym sessions for your first attempt.
- Prepare your salt and water: Have your hydration strategy ready before the hunger hits.
- Audit your "refeed" meal: Ensure you have high-quality protein (like steak, chicken, or eggs) and healthy fats ready to break the fast, rather than high-carb processed foods.