Not Eating But Not Losing Weight? Six Honest Reasons

By Paul Butler · Online Coach & Personal Trainer

There are few things more demoralising than being hungry and unrewarded. It is the fitness equivalent of paying for a gym you never get into.

If you are not eating much and not losing weight, the first thing to say is that you are not imagining it and you are not uniquely broken. It is one of the most common things people bring me, and there are a handful of real, unglamorous explanations. The second thing to say, and I mean this, is that the answer is almost never to eat less again. That is the move everyone reaches for, and it is the one that reliably makes the next month worse.

Here are the six reasons this actually happens, in rough order of how often they turn out to be the culprit.

One: you are eating more than it feels like

Let me get this one out of the way first, and let me be careful about how I say it, because it usually gets delivered as an accusation and it should not be.

In a well-known 1992 study, researchers took a group of people who said they could not lose weight despite eating very little, and measured what they actually ate and burned using proper laboratory methods rather than diaries. The people in that group were under-reporting their food by an average of 47%, and over-reporting their exercise by around 51%. Their metabolisms were normal. The maths was not.

Two important caveats. That group was tiny, ten people, so treat it as a striking illustration rather than a precise law. And more importantly: this is not lying. Almost nobody in that study knew they were doing it. Estimating food is genuinely hard. Oil in the pan, the milk in four coffees, the handful while cooking, the child's leftovers, the weekend that gets remembered as "one meal out". None of it feels like eating. All of it counts.

So the useful version of this reason is not "you are eating too much". It is "your measuring instrument is a human brain, and it is not very good at this". If you want to know whether it applies to you, weigh and log everything honestly for one week, weekends included. Not forever. One week, as a survey rather than a sentence. Most people find something they had not counted, and it is usually liquid or it is usually Saturday.

Two: the fat is going, the water is hiding it

This one is enormously common and almost nobody believes it until they see it break.

Your body weight swings by a few pounds day to day from water alone: salt, carbohydrate intake, hormones, and stress. Dieting itself raises cortisol, and cortisol encourages you to hold water. So you can genuinely be losing fat for two or three weeks while the scale sits perfectly still, and then drop three pounds overnight for no apparent reason. Nothing changed on the day it moved. The scale just caught up.

This is why I ask people to compare weekly averages rather than individual mornings, and why judging a fortnight of hard work by a single reading is a fast way to quit something that was working. If your clothes fit differently and your training is going better, the scale is the thing that is wrong, not you.

Three: eating less has quietly made you move less

This is the reason nobody sees coming, because it does not feel like a choice.

When you cut food hard, your body economises on movement without consulting you. You fidget less. You take the lift. You stand up less often. You walk more slowly. None of it registers as a decision, and across a day it can add up to a few hundred calories of activity that has quietly gone missing.

So the deficit you designed on paper gets partly cancelled by an energy saving you never agreed to. The more aggressively you cut, the bigger this effect tends to be, which is one of several reasons that gentler deficits often outperform brutal ones in practice. It is also why step count is worth tracking during a diet: not to burn more, but to notice when your body starts quietly turning you down.

Four: the deficit only exists Monday to Friday

Five disciplined days and two relaxed ones can average out to no deficit at all, and it will genuinely feel like you have been dieting all week, because you have. For five sevenths of it.

The maths is unforgiving here. A 500 calorie daily deficit across five days is 2,500 banked. Two days that run 1,250 over, which is one meal out and some drinks, clears the lot. Nobody did anything outrageous. The week just netted zero.

The fix is not to ban weekends, which never survives contact with real life. It is to make weekdays slightly less severe and weekends slightly less loose, so the whole week lands in a deficit rather than swinging between famine and festival. I went through the practical version of this in how to stick to a calorie deficit, including banking calories in advance for a night out.

Five: you have lost muscle and lowered your own engine

If you have been eating very little for a long stretch, with no strength training and not much protein, some of what you lost will have been muscle.

Muscle is metabolically active tissue. Lose enough of it and your body burns less at rest than it used to, so the intake that once produced weight loss now produces nothing. You have, without meaning to, made yourself harder to diet. It is the cruellest version of this problem because the harder you tried, the more likely it is.

The way out is not less food. It is protein and resistance training, so that what you are losing is fat rather than the machinery that burns it. This is the same argument I make about how quickly you can lose a stone, and it applies double here.

Six: something medical is involved

Less common than the internet suggests, but genuinely real, and worth ruling out rather than assuming.

An underactive thyroid can slow things down. Several common medications cause weight gain or fluid retention, including some antidepressants, steroids and contraceptives. Conditions like PMOS (which you may know by its old name, PCOS) affect how the body handles food. None of these make weight loss impossible, but they change the terms, and finding out is a blood test rather than a guessing game.

Please go and see a GP if you are eating very little and genuinely nothing is happening, particularly if you also feel exhausted, cold, low, or your hair or skin has changed. That is information you want, and it is a much better use of a month than cutting to a thousand calories to see what happens.

And one more thing, because the people who land on this question are often further down the road than they let on. If eating very little has stopped feeling like a strategy and started feeling like something you cannot ease up on, or if the thought of eating more is frightening rather than just annoying, that is worth proper support rather than a coach's checklist. Your GP first, and the eating disorder charity Beat alongside, who will talk to you long before you meet anyone's idea of a threshold. Anxiety and weight pull on each other in both directions, which I went through in does anxiety cause you to lose weight and again in can losing weight cause anxiety.

What about starvation mode?

Worth addressing directly, because it is the first thing people are told and it is mostly wrong.

The version circulating online, where eating too little makes your body cling to fat so you cannot lose weight at all, is not real. If it were, famine would not be a health crisis. What is real is more modest: eat less for long enough and your body burns somewhat less, partly through the movement effect above and partly through genuine adaptation. It slows progress. It does not stop it, and it does not make you gain weight from nothing.

The reason this myth is worth killing is that it gets used to justify both extremes: eat almost nothing because you have "damaged your metabolism", or give up entirely because your body is "fighting you". Neither is what the evidence describes. Your body is not sabotaging you. It is doing sensible book-keeping.

So what should you actually do?

Almost always the opposite of the instinct.

Eat a bit more, not less, and hold it steady for a few weeks. Get protein into most meals. Add two strength sessions. Track your steps and keep them honest. Weigh yourself weekly and compare averages rather than single mornings. Give it a month before you judge it. If your intake has been very low for a long time, easing it back up will often produce a small, temporary rise on the scale as water and food volume return. Expect that, so it does not frighten you off in week one.

And if the reason you are eating very little is that stress has flattened your appetite rather than that you chose it, that is a different problem with a different answer, which I covered in why anxiety makes you lose your appetite. Worth reading if it rings true.

Frequently asked questions

I am eating 1,200 calories and not losing weight. Is that possible?

It is possible for the scale to stall at that intake for weeks, usually through water retention or a drop in daily movement. What is very unlikely is that you are burning less than 1,200 across a whole day. Before cutting further, log a full week including weekends, then see a GP if it genuinely holds up.

How long should I wait before deciding something is wrong?

Judge it on three to four weeks of weekly averages, not days. Two weeks of a still scale is well within normal noise. If four weeks of honest, consistent eating produces nothing at all, that is the point to change something or get checked.

Should I do more cardio instead of eating less?

More walking, usually yes, because it adds movement without much fatigue. Piling on hard cardio while already underfed tends to backfire: it increases hunger, deepens the fatigue that reduces your everyday movement, and costs muscle. Steps and strength beat punishment.

Does eating too little actually damage your metabolism permanently?

No. Prolonged restriction can lower your energy burn somewhat, largely through lost muscle and reduced movement, and both of those are recoverable by eating adequately and training. There is no permanent broken switch, despite how often that gets claimed.

Why does the scale jump up when I start eating more again?

Because food and stored carbohydrate carry water with them. Eating more after a long restriction adds a few pounds of that within days, and none of it is fat. It typically settles within two to three weeks, which is exactly why you should judge this on a month rather than a Monday.

Is it normal to feel cold and tired while dieting?

Mild versions are common when intake is low. Persistent cold, exhaustion, hair thinning or feeling faint are not things to push through, and they are worth a GP appointment rather than a smaller portion. Those symptoms can point to a thyroid issue or to simply eating far too little for too long.

This article is general information from a coach, not medical advice. If you are eating very little and not losing weight, or you feel exhausted, cold or unwell, please see your GP: thyroid problems, medication and other conditions can all be involved. If eating has become distressing or feels out of your control, contact Beat, the UK eating disorder charity, on 0808 801 0677. Research cited: Lichtman et al., New England Journal of Medicine, 1992, linked in the text. Images sourced from Pexels (free to use): Anete Lusina, Leticia Alvares.