The 1200-calorie diet: why it is too low for most women

Type "lose weight fast" into almost any tracking app and it hands you 1,200 calories. For most women who train, that isn't an ambitious target — it's one that falls apart in about three weeks, usually taking some muscle with it. Here's why the number is too low, and how to find one that isn't.

Where the number 1,200 comes from

Nobody calculated 1,200 for you. It's a round figure handed down through decades of popular diet plans as a sort of lower limit, and apps often use it as a floor once you ask them for a kilo a week.

The same figure lands on a 50 kg woman with a desk job and on a 78 kg woman who lifts four times a week. One number, two completely different bodies.

What you actually burn in a day

Resting metabolic rate — what it costs simply to lie still and breathe — usually works out somewhere between 1,300 and 1,500 calories for a woman of 60 to 75 kg. That's before you get out of bed.

Add walking, work, housework and general moving about, and most women land between 1,800 and 2,300 calories a day. A 45 to 60 minute strength session adds roughly 150 to 250 on top, which is less than people expect, though it accumulates across a week.

Calculators are estimates rather than measurements, and being 10 to 15 per cent out in either direction is normal. Treat the number as a starting point you then test on yourself.

What doesn't fit into 1,200 calories

Take a woman of 68 kg. To hold on to muscle while losing fat, she needs roughly 1.6 to 2.2 g of protein per kilo, so about 110 to 150 g. That alone is 440 to 600 calories.

Fat shouldn't really drop below about 0.6 to 0.8 g per kilo, both for hormones and for absorbing fat-soluble vitamins — call it another 40 to 55 g, or 360 to 500 calories. What's left for carbohydrate is somewhere between 100 and 400 calories: 25 to 100 g for the whole day, less than you'll get through in one honest leg session.

Below roughly 1,400 to 1,500 calories it also becomes hard to cover iron, calcium, vitamin D and 25 to 30 g of fibre. Not because you've chosen badly, but because there isn't enough food in the day to carry them.

What breaks when you undereat for too long

Training quality goes first. Sets you handled with 40 kg last month feel heavy at 32, and recovery stretches out by a day compared with what you're used to.

Then unplanned movement drops. You walk less, sit more, fidget less. Daily expenditure falls without you deciding anything, the scale stalls, and the number on paper still looks correct.

For some women the menstrual cycle goes too. Sports nutrition often uses a rough threshold of around 30 calories per kilo of fat-free mass as the point below which hormonal function starts to suffer; for someone carrying 48 kg of fat-free mass that works out at about 1,450 calories of available energy, before training is subtracted. The evidence here isn't fully settled, but the direction is consistent.

And then the familiar part: three disciplined weeks followed by a weekend that undoes them. That's a predictable response to prolonged hunger, not a character flaw.

A deficit that holds, and how to find your own number

If you can spare a fortnight, measure instead of guessing. Eat the way you normally eat, log all of it, and weigh yourself each morning under the same conditions. If your weight is steady, your average intake across those two weeks is your maintenance.

Take 300 to 500 calories off that. It usually produces 0.3 to 0.6 kg a week, around 0.5 to 1 per cent of body weight — the pace at which muscle mostly survives. For the large majority of women that means eating between 1,500 and 1,900, not 1,200.

If you're under 160 cm and under 55 kg, maintenance might genuinely sit near 1,600, and a sensible deficit lands at 1,300 to 1,400. That's a different thing from treating 1,200 as everyone's default. For numbers broken down per meal, our guide to eating for definition sets them out.

Two things protect muscle better than cutting calories further: lifting two or three times a week, and hitting your protein. How much your body asks for shifts across the decades, which we covered in strength training in your 20s, 30s and 40s, and after menopause muscle loss speeds up, so the deficit should be gentler still.

After 8 to 12 weeks of dieting, spend two or three weeks back at maintenance. It isn't lost time — it's what lets you carry on.

When to see a doctor

Book an appointment if your period has been absent for three months or more, if you go light-headed on standing, if your hair is coming out in handfuls, or if you're cold all the time. The same applies to constant fatigue despite decent sleep — that can be low iron or a thyroid problem rather than poor willpower.

If you have a diagnosis that affects body weight, such as PCOS and insulin resistance, build the plan with someone who knows that condition. And if food is taking up most of your thinking, or you're swinging between very strict days and binges, speak to a professional sooner rather than later.

The short version

• 1,200 is a round number inherited from old diet plans, not an estimate of your needs; most women burn 1,800 to 2,300 a day.
• 110 to 150 g of protein, enough fat and any useful amount of carbohydrate won't fit into 1,200 calories — something always gets squeezed out.
• A workable deficit is 300 to 500 calories below maintenance, which gives 0.3 to 0.6 kg a week.
• Lifting two or three times a week plus adequate protein protects muscle far better than cutting calories further.
• Missing periods, dizziness, hair loss or obsessive thoughts about food are reasons to see a doctor.