Intermittent Fasting: Who It Actually Makes Sense For

What intermittent fasting really does, which formats exist, who it suits and who it does not, plus concrete numbers for protein, training and tracking.

Intermittent fasting gets sold as a trick that burns fat while you sleep. It is a meal schedule and nothing more — a tool that makes eating in a deficit easier for some people and needlessly harder for others. Here is who it actually suits, who it does not, and how to run it if you decide to try.

What fasting actually does

When studies match calories and protein between groups, the difference in fat loss between fasting and a normal three-to-five-meal schedule is small — usually under 1 kg over 8 to 12 weeks, and often not meaningful at all. So fasting does not burn fat by itself. What it does is cut down the number of chances you have to eat.

If your day looks like this — coffee with milk and a pastry at 7, someone brings snacks at 10, lunch, then two more coffees with a biscuit — you have picked up 400 to 700 kcal you never noticed. An 8-hour window deletes most of that without weighing a single thing. That is the whole mechanism.

The formats people actually use

14/10 — you eat within a 10-hour window, say 10:00–20:00. Easiest entry point; most people are already close to this.
16/8 — an 8-hour window, say 12:00–20:00. The most common version and enough for almost everyone.
5:2 — five normal days, two non-consecutive days at 500–600 kcal. Works for people who find two hard days easier than a daily limit.
20/4 and 24-hour fasts — little extra benefit, plenty of problems if you lift. Skip them.

Who it makes sense for

People who already skip breakfast and eat first around noon — for them fasting is just a new name for what they do anyway.
People who hate counting calories and weighing food but need a 300–500 kcal daily deficit.
Desk workers who prefer two big meals of 700–900 kcal over five small ones.
People whose main problem is evening snacking — a later window like 13:00–21:00 means you are full exactly when it is hardest.

Who it does not make sense for

Fasting is not neutral for everyone. These are the situations where it works against you or is simply the wrong tool:

You are building muscle and need 3,000 kcal or more — cramming that into 8 hours is miserable and usually ends with you eating too little.
You train at 6:30 in the morning and your window opens at 12:00 — you train hungry with no meal after, and strength drops within 3 to 4 weeks.
You have a history of disordered eating. A rule like I am not allowed to eat until noon turns into a restrict-then-binge cycle very easily.
Pregnancy and breastfeeding.
Type 1 diabetes, or type 2 on insulin and sulfonylureas — the hypoglycaemia risk is real.
You regularly eat 1,000 kcal over plan once the window opens. Then the format is costing you, not helping.

If you try it, do it like this

Ramp up: week one 12/12, week two 14/10, week three 16/8. Jumping straight to 16 hours usually lasts about four days.
Protein comes first: 1.6–2.2 g per kg of bodyweight. At 80 kg that is 130–175 g a day, split into 3 meals of 45–58 g.
Put training 2–3 hours after your first meal. If you must train fasted, get 40–50 g of protein in within 60 minutes afterwards.
Do not change your program because of the schedule: main lifts 3–4 sets of 5–8 reps, accessories 3 sets of 8–12. If you can no longer hit those numbers, the problem is the food, not the program.
Drink 2.5–3.5 litres a day and do not cut salt — a good share of first-week headaches is plain dehydration.
Weigh yourself 3–4 mornings a week and read the weekly average, never a single day. A realistic rate is 0.5–0.75% of bodyweight per week, so 0.4–0.6 kg for an 80 kg person.

Signs it is not working for you

Give it three weeks, then check:

Working weights are down more than 10% — you squatted 100 kg for 5 reps, now 90 kg feels heavy.
Dizziness, headaches or shakiness that have not settled by the end of week two.
Worse sleep, or waking up hungry around 3 a.m.
In women: an irregular or missing cycle.
You think about food constantly and count the hours until the window opens.

None of that is a discipline problem — it just means the schedule does not fit you. Three meals and a 400 kcal deficit produce exactly the same result.

When to see a doctor

Before you start, if you have diabetes or take insulin, blood pressure medication or thyroid medication — doses and timing often need adjusting.
If a medication has to be taken with food and that dose falls inside the fasting period.
Fainting, a very fast resting heart rate, or confusion during a fast — same day, do not wait it out.
Losing more than 1 kg a week for over a month, or a body mass index below 18.5.
Any history of disordered eating — talk to a professional first, then decide on a meal schedule.

The short version

Fasting does not burn fat on its own — it removes chances to eat, and that is the entire benefit.
16/8 is plenty; 24-hour fasts add nothing and interfere with lifting.
Protein stays at 1.6–2.2 g/kg regardless of the window: for 80 kg that is 3 meals of 45–58 g.
If strength drops more than 10% over three weeks or you overeat once the window opens, the format is wrong for you.
Diabetes, pregnancy, breastfeeding and a history of disordered eating mean doctor first, decision second.