Fasting · 11 min read

16:8 vs 18:6 vs 20:4 vs OMAD: Which One People Actually Keep

Written by Coach Ohm · reviewed 2026-08-30

Try it: Intermittent Fasting Window Planner — Get a full-day schedule that puts your eating window where your training actually is.

Every protocol comparison ranks these by how much weight you lose. That is the wrong axis. The one that matters is how many people are still running it in month three.

The trade that defines all of them

Longer fast, shorter window. Shorter window, fewer meals. Fewer meals, less total food for most people without counting anything — and also a harder schedule to keep, a harder protein target to hit, and a tighter fit around family meals and work.

The aggressive protocols produce faster short-term change and are abandoned sooner. The gentle ones produce slower change and are still running when the aggressive ones have stopped. Over a year, slower and still running wins comfortably.

14:10 — the version that is barely a protocol

Stop eating at 8 p.m., eat again at 10 a.m. For a lot of people this is roughly what they already do, minus the evening snacking. That is precisely why it works: it removes the single highest-calorie, lowest-satisfaction eating occasion of the day without demanding anything else.

Best for: anyone who has never fasted, anyone whose main problem is eating after dinner, anyone with a family evening meal they will not move.

16:8 — the default for good reasons

Eight hours to eat is enough for two full meals and a snack, which means protein targets are reachable and social meals survive. It is the protocol most people can describe to their family without an argument.

Best for: most people, most of the time. If you are unsure which to pick, pick this one and give it eight weeks before considering anything more aggressive.

18:6 — the first real step up

Six hours is two meals, comfortably, and not much more. The additional two hours of fasting past 16:8 delivers a modest additional benefit and a noticeably harder schedule — the window usually has to sit in the afternoon and evening, which starts to conflict with morning training and with breakfast as a social event.

Best for: people who have run 16:8 for at least a month and want to tighten it. Not a starting point.

20:4 — advanced, and the protein problem appears

Four hours is realistically two meals close together. This is where hitting a protein target of 150 grams or more stops being automatic and starts requiring planning. It is also where sessions scheduled outside the window become genuinely awkward.

Best for: experienced fasters with simple schedules and modest training loads. Poor fit for anyone lifting heavy four or more times a week.

OMAD — highest short-term change, lowest survival rate

One meal a day produces the fastest weight change of the group and the shortest average run. The reasons are predictable: a single meal large enough to carry a day's protein and energy is genuinely uncomfortable, social eating becomes nearly impossible, and the psychological pressure on that one meal is high.

Best for: short defined blocks, or people whose schedule genuinely suits it. Not a long-term default, and not a first protocol.

5:2 — a different mechanism entirely

Eat normally five days, restrict heavily on two non-consecutive days. This works through a weekly deficit rather than a daily window, so it fits people whose days are too unpredictable for a fixed window. The trade-off is that the two restricted days are genuinely hard rather than mildly inconvenient.

How to actually choose

Ask three questions and let the answers decide.

When do you train? Early morning training and a late window are a bad pair. See fitting the window around training.
What is your protein target? Over about 150 grams, a four-hour window is a real constraint. Check with the protein calculator before committing.
What meal is non-negotiable socially? If it is family dinner, the window ends late and everything else arranges around that.

The upgrade path

Start one step easier than you think you need. Hold it for four weeks without a missed day. Then, and only then, consider tightening by two hours. Most people who go straight to 20:4 are back to eating whenever within a month, which leaves them worse off than if they had run 16:8 the whole time.

A worked example: one protein target, four windows

Take a 32-year-old man, 175 cm, 80 kilograms, training moderately three to five days a week. His maintenance calories work out to 2695 a day, and a comfortable rate of loss of 0.25% of bodyweight per week puts his target at 2475 — a 220-calorie daily deficit. Training at that level, his protein range is 128 to 160 grams a day. Nothing about that changes when he changes fasting protocol. What changes is how those grams have to be divided.

Window	Typical meals	Protein per meal
16:8	3	~43–53 g
18:6	2	~64–80 g
20:4	2, tight	~64–80 g in less time
OMAD	1	128–160 g

The total never moved. What moved is the size of each dose and how much room there is to recover from a meal that goes wrong. On 16:8, missing one meal's protein by 20 grams is fixable at the next one. On OMAD, there is no next one — that meal is the whole day's protein, and if he is not hungry, gets interrupted, or the food on hand is wrong, the day is already lost by the time he finds out.

Two more worked cases

A 25-year-old woman, desk job, 65 kilograms, targeting a faster 0.5% of bodyweight per week, lands at 1637 maintenance calories and a target of 1279 — a 358-calorie deficit. Her strength protein range is 104 to 130 grams. On OMAD, that whole range plus 1279 calories has to fit into one sitting, comfortably above her 1200-calorie floor but not by a wide margin. That is a genuinely large single meal for someone with a desk job and no training-driven reason to need that much food at once. For her, 16:8 or 18:6 fits the numbers far more comfortably than OMAD does, independent of preference.

A 45-year-old man, 95 kilograms, training one to three days a week, targeting a more aggressive 0.75% of bodyweight per week, lands at 2551 maintenance calories and a target of 1767 — a 784-calorie deficit. His strength protein range is 152 to 190 grams. On 20:4, that is close to 190 grams inside a four-hour window on top of the rest of a 1767-calorie day. It is possible with planning — see hitting protein on a short window — but it is not a starting point. He reaches the same deficit either way; 16:8 gets him there without turning every day into a protein-logistics exercise.

Neither of these people is unusual. This is the ordinary shape of the mismatch between an aggressive protocol and a real protein target, and it is why the choice of protocol should follow from the numbers rather than from which one sounds most disciplined.

Where each protocol actually breaks

The comparisons above assume an ordinary day. Ordinary days are rarely the ones that end a fasting protocol. These are.

Travel and irregular schedules

A flight, a meeting that runs through the window, a time zone change — anything that shifts the window by more than an hour or two is a bigger problem on a short window than a long one. On 16:8 an hour's slip barely registers. On OMAD, an hour's slip can mean the one meal happens at 11 p.m. instead of 7, which wrecks sleep and makes the next day harder before it has even started.

A session that gets pushed later

Sessions that move later collide with tight windows more often, simply because there is less window left for the collision to land in. A morning lifter running 16:8 with a noon-to-8pm window has slack if the session runs long. The same lifter on 20:4 with a 4pm-to-8pm window does not.

A meal inside — or outside — the window

Dinner with people who are not fasting is the single most common reason 18:6, 20:4 and OMAD get abandoned. Not because the food is wrong, but because the window has to bend around one meal and there is no longer enough window left for the rest of the day's food.

Hunger that will not settle

Most people adapt to a fixed window inside two to three weeks. If hunger at the same time every day is not easing off after a month, that is not a willpower problem — it is a sign the window does not fit the person's actual training load, sleep pattern, or schedule, and persistence alone does not fix that.

The day something goes wrong

Every protocol above will eventually meet a day it does not survive intact — illness, a family emergency, a schedule that collapses. What you do next matters more than what happened.

Eat when you need to and pick the protocol back up at the next natural window. Do not compensate by fasting longer the next day, and do not try to make up a missed protein target by cramming it into the following one. One disrupted day changes almost nothing measured over months. Turning a disrupted day into a punitive correction is what actually derails a protocol, because it teaches you the plan is fragile — and a plan you believe is fragile is one you eventually stop trusting.

Signs you picked the right one, and signs you picked wrong

Right fit: hunger arrives at predictable times and fades once you are used to the schedule. You can describe the window to your family in one sentence. You are hitting your protein target without heroics.
Wrong fit: hunger arrives at unpredictable times, protein is consistently short, training quality is dropping faster than the weight loss would explain, or you are negotiating exceptions most days rather than occasionally.

The clearest single test is the one from earlier: track one honest day of protein. If a short window is quietly costing you 30 or 40 grams a day, that is the protocol failing you, not the other way around. See hitting protein on a short window for the fix before deciding the whole approach does not work for you.

What the window does not tell you

A fasting window controls when you eat. On its own it does not control how much, what, or whether the weight you lose is fat or muscle. Three things it says nothing about:

Whether you are actually in a deficit. A short window with two very large meals can still add up to maintenance calories or more. The window changes timing, not arithmetic.
Whether you are protecting muscle. That is decided by protein intake and continued resistance training, not by the number of hours you fast. A tight window that costs you protein works against this goal even while the scale keeps moving the right direction.
Whether it fits your life six months from now. Short-term compliance and long-term compliance are different questions, and the aggressive protocols answer the first one better and the second one worse.

Reassessing after the first plateau

When weight loss stalls, the instinct is to tighten the window further. Usually the better move is to check the two things a window cannot fix on its own: is the deficit still real after weeks of the same routine, and is protein still landing where it needs to. Tightening a window that is already costing you protein just stacks a second problem on top of the first.

Heavy lifting versus cardio versus both

Training type interacts with window length differently than most people expect. A pure cardio schedule is fairly forgiving of a tight window, because a single easy-to-digest post-session meal covers most of what the session needed. Heavy lifting is less forgiving, mainly because the protein target is higher and because performance on a big compound lift is more sensitive to being underfed going in.

If you do both — lifting three or four times a week plus separate cardio sessions — the honest answer is that you have more to fit into the window, not less. This is the group for whom 16:8 or 18:6 tends to hold up best over a full training block, and the group where 20:4 and OMAD most often quietly erode performance before the person notices the scale has stopped moving too.

Shift work and parenting schedules

Fixed-window protocols assume a fixed day. Rotating shifts and unpredictable school or childcare schedules break that assumption more than any other factor covered here. Two adjustments make a real difference: anchor the window to the activity that repeats — the shift start, the school drop-off — rather than to a clock time, and pick the gentler end of the range on purpose. A rotating-shift worker running 14:10 or 16:8 tied to "the hour after I wake up" tends to hold the habit far longer than the same person trying to force an 18:6 window onto a schedule that changes every week.

Parents of young children face a related problem: the evening window is rarely under their own control. If dinner happens whenever the kids are fed and settled, build the window around that fixed point rather than against it, and accept that some days will run long. A protocol that bends without breaking beats one that is technically stricter but gets abandoned the first week the schedule falls apart.

One protocol, tried honestly, beats three tried briefly

A pattern worth naming: people who cycle through 16:8, then 18:6, then OMAD, then back to 16:8 inside a single month rarely give any of them a fair test. Each restart resets the adaptation clock — the two to three weeks it takes hunger to settle into a schedule — so the person experiences nothing but the uncomfortable early phase, over and over, and concludes that fasting itself does not work for them. Pick one, commit to the four weeks from the upgrade path above, and only then judge it.

Write down which protocol you are running and the date you started it. It sounds unnecessary until the third week, when the temptation to switch is strongest and the memory of why you chose this one in the first place has already faded. A one-line note settles the argument with yourself in about five seconds.

None of this replaces judgment. A protocol that fits the numbers on paper can still be wrong for a specific person in a specific season of life, and a protocol that looks aggressive on paper can still be the right one for someone whose schedule genuinely suits it. The numbers narrow the choice. The four weeks of actually living with it decide the rest.

If you are still unsure after reading all of this, that uncertainty is itself useful information: pick the gentlest option on the list, run it properly, and let the result tell you whether tightening further is worth trying at all.

The fasting window planner will lay out any of these against your actual training time, including whether the session lands somewhere sensible.

Questions I get asked

Which protocol burns the most fat?

Over weeks, the one that produces the largest sustained energy deficit — which for most people is the one they keep doing, not the strictest one.

Can I change protocols day to day?

You can, but a consistent window is where most of the practical benefit comes from. Hunger settles into a schedule it can predict.