Upvaas means “to dwell near,” not “to go without.” Here’s what a 24-hour fast actually does to a South Asian metabolism — tracked, hour by hour.
Four months ago I started doing something that would have sounded insane to me a couple of years back: once a month, I stop eating for a full 24 hours. Dinner one evening, then nothing until dinner the next day. LMNT electrolytes in water first thing in the morning, two or three espressos through the day until about 1pm, and that’s it.
I want to be honest about what this is and isn’t. My everyday routine is a boring 16:8 — the sort of intermittent fasting plenty of Indians have quietly taken up over the last few years: dinner at 6:30, first thing the next morning is a protein smoothie around 10:30. I’ve written about that already: it’s how I keep my body able to switch between burning sugar and burning fat, and it’s the version I’d recommend to almost anyone. The monthly 24-hour fast is a different animal. It’s not a weight-loss tool. It’s closer to a reset — a deliberate, once-a-month stress test that pushes my metabolism somewhere the daily fast never quite reaches.
And the strange part is how familiar it felt once I started. Because I didn’t invent this. Nobody did. Every year during Paryushana, the Jain festival, my mother-in-law fasts — really fasts, with a discipline that makes my one day a month look like a warm-up. When I decided to do my monthly fast around the same window she keeps hers, it stopped feeling like a biohacking experiment and started feeling like something much older that I was quietly rejoining. She’d have been amused that I needed a ketone meter to arrive at it.
The word we lost in translation
Here’s the thing almost every English article about “Indian fasting” gets wrong. We translate upvaas as “fast,” and then we picture deprivation — an empty stomach, willpower, going without.
That’s not what the word means.
Upvaas comes from the Sanskrit upa (near) and vas (to dwell). It literally means “to dwell near.” Near what? Near the divine. In the original framing, the food was never the point. Skipping the meal was just the method — a way to quiet the body’s constant background hum of eating and digesting so that your attention could sit somewhere else. The heaviness lifts, the energy that normally goes into breaking down lunch is freed up, and you become, for a day, a bit more available to whatever you’re trying to be near.
And it isn’t only the Hindu-Sanskrit word that points this way. Paryushana — the Jain festival my mother-in-law observes — is usually translated as “abiding” or “coming together,” and one traditional reading is staying near your own soul, from all directions. Two different desi traditions, one Hindu and one Jain, built their most serious fasting practices around the same idea: not going without, but drawing near. That’s not a coincidence. It’s a clue about what fasting was actually for.
I find that reframe genuinely useful, and not for spiritual reasons. It’s a completely different mental model than “I’m restricting.” One is subtraction. The other is making room. When I’m deep into a fast and my mind gets that clean, slightly lit-up quality (more on exactly when, and why, later), the “making room” framing describes the experience far better than “I’m hungry and depriving myself” ever did.
Fasting didn’t start as a health hack. It started as survival.
The deeper history is worth sitting with, because it explains why any of this works on our bodies at all.
For almost all of human existence, fasting wasn’t a choice. Anthropologists who study early humans describe food as unpredictable — seasonal shortages, failed hunts, the long gap between one harvest and the next. Going without for a day or two wasn’t a practice. It was Tuesday.
What every major culture then did — independently, on nearly every continent — was take that involuntary scarcity and ritualize it. They took the lean stretch that was coming anyway and wrapped it in meaning. You can still see the agricultural fingerprints on these traditions if you look. The Christian season of Lent, for instance, lines up almost exactly with the late-winter “hungry gap”: the weeks when last year’s grain stores were running low and the spring harvest hadn’t come in yet. The community was going to eat less regardless. Turning that shortage into a sacred fast made a virtue out of necessity — and, crucially, made it survivable and shared instead of frightening and lonely.
In the Indian tradition, this got codified early. Fasting shows up in Vedic, Hindu, and Jain practice going back roughly three and a half thousand years. And it wasn’t reserved for once-a-year drama. Ekadashi — the eleventh day of each lunar fortnight — brought a lighter day twice a month, framed in part as giving the hardest-working organ in the body, the digestive system, a scheduled day off. Twice a month. For centuries. Long before anyone had heard the phrase “intermittent fasting.”
Even Paryushana carries the season in its bones. The festival grew out of cāturmāsa, the four-month monsoon retreat when wandering Jain monks stopped traveling and settled in one place while the rains came down — a time when movement, farming, and foraging all naturally paused. The calendar wasn’t arbitrary. It tracked the year’s rhythms, and the fasting tracked the calendar.
Our ancestors didn’t have the mechanism. They had the pattern. And the pattern turns out to be the part that matters.
Why this lands differently on a desi body
This is where it stops being history and starts being personal.
There’s a long-standing (and, I’ll be fair, still-debated) idea in metabolic science called the thrifty phenotype. The rough version: populations that survived repeated cycles of feast and famine may have been shaped — over generations — toward metabolic “thriftiness.” Bodies that were exceptionally good at storing energy when food was around, because the famine was always coming.
That trait is a superpower when scarcity is real. It becomes a liability the moment scarcity disappears. And that, in one sentence, is a large part of why South Asians develop insulin resistance, fatty liver, and type 2 diabetes at lower body weights than most other populations. Our metabolism is, in a sense, still braced for a famine that modern life quietly cancelled.
Now look at what upvaas actually was, mechanically. It was the cultural machinery that kept the feast-famine cycle turning — even in years when the crops were good. Twice-monthly Ekadashi, seasonal fasts at the turn of the year, the fast before a festival. These weren’t nutrition science. But they kept reintroducing the “famine” half of a cycle our bodies were built around.
Modernity kept the feast and deleted the fast. We have the abundance our ancestors prayed for, twenty-four hours a day, and a metabolism that never gets the pause it evolved to expect. When I do a monthly 24-hour fast, I’m not doing something exotic. I’m putting back the half of the rhythm that my own family kept for generations and I somehow dropped.
What actually happens in a 24-hour fast
So what does a full day without food do that my daily 16:8 doesn’t?
The core event is what researchers Rafael de Cabo and Mark Mattson, in a widely-cited 2019 New England Journal of Medicine review, call the metabolic switch. Somewhere past roughly twelve hours without food, your liver’s glycogen — its stored sugar — runs low. The body responds by pulling fat out of storage and shipping it to the liver, which turns it into ketones. You flip from running on sugar to running on fat.
My everyday 16:8 gets me to the edge of that switch, especially with a fasted morning workout to burn down the glycogen faster. A 24-hour fast doesn’t just cross the line — it keeps me on the far side of it for hours and hours, deep into fat-burning territory that the daily fast only touches.
I can watch it happen on my meter. Here’s a typical fast day, checking my blood ketones with a finger-prick meter:
| Time | Hours fasted | Ketones (mmol/L) | What that reading means |
|---|---|---|---|
| 6:00 am | ~12 | 0.2 | Below 0.5 — not in ketosis yet; still coasting on last night’s dinner |
| 10:00 am | ~16 | 0.8 | 0.5–1.0 — light nutritional ketosis; the switch has flipped on |
| 2:00 pm | ~20 | 1.1 | 1.0–1.5 — nutritional ketosis; solidly fat-fuelled now |
| 6:00 pm | ~24 | 1.4 | Still nutritional ketosis, deeper end; running mostly on fat |
For reference: under 0.5 mmol/L isn’t ketosis at all. Roughly 0.5–3.0 is “nutritional ketosis,” the everyday fat-burning zone a fast like this lives in. The much higher “therapeutic ketosis” ranges you’ll see quoted (3.0+) are pursued only under medical supervision for specific conditions — they are not the point of a monthly fast, and I never go near them.
That’s the switch, drawn in real time. At 6am I’m barely producing ketones — still mostly coasting on last night’s dinner. By afternoon the number is climbing steadily, and by the time I break the fast I’m at 1.4, genuinely running on fat.
And here’s the part I didn’t expect, which lines up almost too neatly with that curve. The hardest stretch of the whole fast is late morning into midday — right around when I’d normally be eating breakfast and then lunch. My body clearly still expects food at those hours, and it complains. But then, reliably, somewhere around 2pm, it flips: the hunger quiets and it’s replaced by a clean, slightly wired mental clarity that lasts the rest of the afternoon. Look at the table — 2pm is exactly when my ketones cross into the 1-plus range. Ketones as fuel and as signal, showing up as a mood I can feel. I don’t want to overstate a single person’s meter readings, but the felt experience and the number arrive at the same time, every time.
And ketones, it turns out, aren’t just backup fuel. The same review describes them as signaling molecules — they switch on cellular pathways involved in stress resistance and repair. In parallel, an extended fast lowers a growth pathway called mTOR and raises an energy sensor called AMPK, which together nudge the cell out of “build and grow” mode and into “clean up and recycle” mode. That cleanup process — autophagy, the discovery of which won a Nobel Prize in 2016 — is the cell dismantling its own worn-out parts for scrap.
Here’s where I have to be straight with you, because a lot of fasting content is not: most of the crisp claims you’ll see about autophagy — “it switches on at exactly hour 16,” “a 24-hour fast clears out damaged cells” — are extrapolated from animal and lab studies. The human timing is genuinely not nailed down. What we can say with more confidence is that the metabolic switch is real and measurable, and that periodic fasting produces meaningful changes even in healthy people: one 2019 study in Cell Metabolism (Stekovic and colleagues) found that alternate-day fasting improved several markers of aging and cardiovascular health in healthy, non-obese adults over four weeks.
So the honest summary is this. A monthly 24-hour fast is not a proven longevity protocol, and anyone selling it as one is ahead of the evidence. What it is: a reliable way to drive the metabolic switch harder than a daily fast can, a plausible (not certain) way to give the cellular cleanup machinery a longer runway, and — for me — a genuinely useful once-a-month recalibration of my relationship with food.
What it is not
Let me kill a few things before they take root.
It’s not a weight-loss strategy. De Cabo and Mattson are explicit that the benefits of fasting aren’t mainly about the calories you skip — and one day a month barely moves the calorie math anyway. If you eat normally the other 30 days, a monthly fast will not, by itself, change your body composition. The daily habits do that.
It’s not a license to binge. The ancient pattern was fast, then break gently — Ekadashi tradition literally warns against eating heavily right after. Following a 24-hour fast with a feast undoes most of the point.
And it’s genuinely not for everyone. If you’re pregnant or breastfeeding, if you’re on blood-sugar or blood-pressure medication, if you have any history of disordered eating, or if you’re underweight, an extended fast is not a wellness experiment — it’s a medical question, and the answer might be no. Talk to your doctor first. This one isn’t negotiable.
If you want to try it
I’m not going to hand you a protocol with hour-by-hour targets, because that’s exactly the mindset upvaas was designed to get away from. But if a monthly reset appeals to you, here’s how I’d start.
Start with the daily rhythm first. If a 16:8 window already feels comfortable, a longer fast is a small extension. If skipping breakfast still feels like a battle, you’re not ready for 24 hours, and that’s fine.
Pick a low-stakes day. My first attempt was on a busy workday, which was a mistake — every meeting felt harder. Now I do it on a quieter day when I can let the afternoon dip pass without fighting it.
Mind your electrolytes — especially if you’re salt-sensitive. When you fast, your body sheds sodium and water. My own genetics flag me as very salt-sensitive, so I don’t skip this: water plus electrolytes through the day makes the difference between a clean fast and a headachy, miserable one.
Break it gently. Something light and real — not the biggest, richest meal you can find. Your gut has had a rest; honor that.
And borrow the old frame. You’re not depriving yourself for a day. You’re making room. Whatever you want to be a little nearer to — clarity, discipline, your own sense of control over your appetite instead of the other way around — a fast is just the oldest tool we have for getting there.
My mother-in-law knows that without a single lab value. She fasts for Paryushana because the tradition asks her to draw near — to her soul, to forgiveness, to something beyond the next meal. I came at it sideways, through a ketone meter and a stack of studies, and landed in the same place: one day a month when I make room. Her road is older and, honestly, wiser. But it turns out both roads lead to the same afternoon — the one where the hunger goes quiet and something clearer takes its place.
A few honest questions people ask me
What does upvaas actually mean?
It comes from Sanskrit — upa (near) and vas (to dwell) — so it literally means “to dwell near,” as in near the divine. The food restriction was always the method, not the goal. The point was to clear away the heaviness of constant eating and digesting to make room for something else.
Is a 24-hour fast better than 16:8?
Not better — different. A daily 16:8 keeps your metabolism flexible and is the habit I’d recommend to most people. A once-a-month 24-hour fast pushes you deeper into fat-burning and keeps you there longer. It’s an occasional reset, not a replacement for the daily rhythm, and it won’t change your body composition on its own.
Is fasting safe if you’re at higher risk for diabetes, like many South Asians are?
For a healthy adult, an occasional 24-hour fast is generally considered reasonable — but “higher risk” and “already on medication” are two very different things. If you take any blood-sugar or blood-pressure medication, are pregnant, are underweight, or have any history of disordered eating, talk to your doctor before trying an extended fast. This isn’t a formality.
This is a personal account and general education, not medical advice. Extended fasting is not appropriate for everyone, and can be genuinely risky for some people. Talk to your doctor before making changes, especially if you take medication or have a history of disordered eating.
