Intermittent fasting is not a diet. It says nothing about what you eat — only when. That is the whole idea, and it is why it appeals to people who have bounced off every diet that came with a shopping list.
This guide covers what it is, what to start with, what the first week is actually like, and — importantly — who should not do it.
What it is
You choose a window of the day in which you eat, and you do not eat outside it. Common schedules:
- 12:12 — twelve hours eating, twelve fasting. Barely a change for most people. A good first week.
- 16:8 — the standard. Eight-hour eating window. See what is 16:8 fasting.
- 18:6 — a tighter window, usually a step up rather than a starting point.
- OMAD — one meal a day. Not a beginner schedule and genuinely hard to hit nutritional needs on.
What to start with
Start at 12:12 for a week, then move to 14:10, then 16:8 if you want it. Most people who fail at intermittent fasting failed at day three of 16:8 having never tried 12:12, and concluded that fasting does not work for them. What did not work was the jump.
The other reason to ramp: it lets you find out how your body handles it while the stakes are low.
What the first week feels like
Hunger arrives in waves, not a climb. This is the single most useful thing to know. The intuition is that hunger will keep rising until you eat. It does not — it rises, plateaus, and recedes. Knowing that a wave passes is most of the skill.
A headache on day two or three is common. It is usually dehydration or caffeine timing rather than the fast itself. Drink more water than feels necessary and add a little salt.
You will discover how much eating was habitual. The 10:30am urge is rarely hunger. It is a slot in your day that has had food in it for years.
Energy often steadies out by week two. Reported, not guaranteed. Some people find fasting makes them irritable and tired, and continues to. That is a real answer too.
What to eat in your window
Fasting is agnostic about this, but two things matter practically:
- Enough protein. A shorter window makes it easy to under-eat protein without noticing.
- Actual meals. A window is not a licence to graze for eight hours. Two or three real meals beats constant snacking, for satiety and for the habit.
You do not need to count anything. If you were going to enjoy counting calories you would already be doing it.
When it goes wrong
Stop and reassess if you are dizzy, if your sleep gets worse, if you find yourself thinking about food constantly, or if breaking the fast has started to feel like losing.
That last one matters most. If a fasting schedule is producing guilt, restriction and a sense of failure, it has stopped being a metabolic tool and started being something else. Put it down.
Who should not do this
Do not start intermittent fasting if you are pregnant or breastfeeding, if you have any history of an eating disorder, if you are under 18, if you have type 1 diabetes, or if you take medication that must be taken with food.
Talk to a clinician first if you have type 2 diabetes, low blood pressure, a history of low blood sugar, or any chronic condition. "I feel fine" is not a substitute for that conversation, because several of the relevant risks do not announce themselves.
A reasonable first month
- Week one: 12:12. Note when you were hungry and whether it passed.
- Week two: 14:10. Move the window earlier or later until it fits your actual life.
- Week three: 16:8 if weeks one and two were uneventful. Stay at 14:10 if not.
- Week four: keep whatever you are still doing without effort. That schedule is your schedule.
A timer helps here mainly because memory is unreliable about start times. Fastrackie does that and shows you which phase you are in, free.