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6 Reasons Why Your Calorie Deficit Isn’t Working

Six reasons why your calorie deficit isn’t working

The fundamental principle of weight-loss is that you have to be in a sustained energy (calorie) deficit over time. Or more simply: over the long term, “calories in” has to be less than “calories out”.

It’s therefore a very common refrain from frustrated customers whose DEXA body scans show beyond doubt that their diet and exercise plan is going nowhere: “Why isn’t my calorie deficit working? Why am I not losing any weight even though I’m eating less and doing more?”

The answer to this simple question is just as simple: “You are not in a calorie deficit!”

That’s it. Pure and simple. If your weight on the scale is not falling over time, then the laws of physics say you are not in a calorie (energy) deficit. Here are six reasons why, despite your best intentions and calculations, you are not in a calorie deficit when you think you are.

  1. Your estimate of your maintenance calories is too high
  2. You are doing less exercise and activity than you think
  3. You’re relying on a fitness tracker
  4. Your current weight is increasing, not constant
  5. You are consuming more food and drink than you think
  6. You are inconsistent

1. Your calorie deficit isn’t working because your ‘maintenance’ calculation is wrong

Your maintenance calories, as discussed here, is the number of calories you can eat for your weight to stay the same (ie, to be ‘maintained’). If you eat below maintenance, you will be in a calorie deficit and your weight will definitely fall.

But calculating maintenance, from which we subtract calories to arrive at a calorie deficit, is a tricky business. It’s nearly always done as a prediction by plugging numbers into a formula and can only ever be an estimate because a one-size formula cannot fit all. Without an accurate means of measuring body composition, such as a DEXA scan, the most common formula to arrive at maintenance is this one (also here on our website) which is based on your age, sex, weight and height.

If you have lower-than-average muscle mass, this standard formula will always over-estimate your resting metabolic rate, from which your maintenance calories are calculated. This means that what you think is a calorie deficit is not a calorie deficit at all and you will never lose any weight; in fact you may gain weight. This video clip explains it clearly.

To arrive at a calorie deficit that works, you need an accurate measurement of your body composition (eg, from a DEXA scan) because it will enable you to use a more accurate calorie deficit calculator which uses your lean body mass as an input. That’s important because most of your calories are burned by lean mass – muscles and organs.

2. You are doing less exercise and activity than you think

Most people have a very inflated (one might say delusional) idea of how much activity and exercise they do. On their first visit to Bodyscan for a DEXA scan, customers describe themselves as “pretty active” or “very active” when they are little more than sedentary!

Walking the dog, gardening, looking after children or being “always on the go” does not constitute an active lifestyle. Sure, you may not be sitting on the couch all day (or maybe you are) and regular movement is good, but the above activities involve no formal, scheduled, extended periods of exercise and won’t get you panting or out of breath.

Bodyscan’s DEXA consultants would classify the activities above as little more than ‘sedentary’ and certainly no higher than ‘light activity’.

Why? Well, let’s put things into perspective – there are 168 hours in a week, so you can see that three to four hours of scheduled exercise equates to just 2% of your week.

And a general point – exercise or scheduled activity is a small daily contributor to creating a calorie deficit. In other words, exercise doesn’t burn many calories.

Look at the extract from our DEXA scan fat-loss calculator, which shows the difference in daily maintenance calories (below) for a typical woman across the full range of activity profiles – about 200 calories a day.

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It’s a small number of calories when you consider an M&S Super Nutty Wholefood Salad, a Pret ham and cheese sandwich and a Pret small flat white coffee contain, in total, nearly 1000 calories.

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When it comes to activity, your calorie deficit will be affected much more by non-scheduled or ‘background’ activity you are barely conscious of – walking instead of driving, using stairs instead of the lift, parking farther from the supermarket entrance, fidgeting, etc. This type of calorie-burn is known as NEAT (non-exercise activity thermogenesis).

3. You’re calculating your calorie deficit with a fitness tracker or app

We’ll be brief on this one – don’t ever (ever) trust a digital readout about how many calories you are burning. Whether it’s a treadmill, rowing machine, Apple Watch, Fitbit, MyFitnessPal, etc. To show we’re balanced and impartial, we’ll even include the Bodyscan calorie calculator we use after a DEXA scan. All these devices give you a number that is an estimate, a best guess as to how many calories you are burning. Don’t take it as gospel truth.

The best reason for having a fitness tracker is simply to encourage you to move more.

4. Your weight is going up when you calculate yor calorie deficit

As we’ve discussed above, your weight falls when you are in a calorie deficit. 

But remember that a calorie deficit takes your maintenance calories as its starting point, and maintenance is the point at which your weight remains constant.

So, if your maintenance calories are 2400 calories, a deficit of 500 calories, say, will mean a daily calorie target of 1900 calories.

But that daily deficit of 500 calories is only valid if you are indeed currently eating at maintenance, and that will only be true if your weight is constant. (At your first Bodyscan DEXA scan, we’ll ask you if your weight has changed over the last few months.)

If, however, you are steadily putting on weight then of course you are eating above maintenance. If you’re eating, say, 2800 calories a day, then a calorie deficit of 500 calories, will see you consume 2300 calories a day, a deficit of just 100. In this case, it will take you FIVE TIMES AS LONG to lose the same amount of weight.

In the above example, the daily target of 1900 calories will require a reduction of 900 calories a day, not 500. That means you’ll have to reduce your consumption by a third.

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5. You’re eating more food and drink than you think

This is closely tied to point (4) above. Even if your weight has remained static before you start your fat-loss journey and you are indeed currently eating at maintenance, subsequent weight-loss results can be disappointing because you do not actually enact a big enough calorie deficit.

Our DEXA scan calorie calculator will give you a pretty reliable number to aim for, but many people just do not appreciate how many calories there are in their favourite or commonly-eaten foods, and so never achieve the required calorie deficit.

The M&S salad and Pret sandwich-and-coffee above come to 960 calories, which is more than half of a typical male’s diet plan and likely two-thirds of a typical female’s.

You don’t have to eat much to overshoot your deficit!

6. Your deficit isn’t working because you are not consistent.

Let’s return to the opening sentence: the fundamental principle of weight-loss is that you must be in a sustained energy (calorie) deficit over time. That means, on average, a calorie deficit every day.

But we are not lab rats and that thing called ‘life’ (weekends, parties, weddings, friends, holidays, alcohol, takeaways) means there will be many days when our intended calorie deficit is wiped out or even reversed into a surplus.

Life happens, so we have to be patient, but at the same time why work so hard on ‘being good’ Monday to Friday, only to make it count for nothing over the weekend?

If you maintain a deficit of 500 calories from Monday to Friday (a total deficit of 2500 calories) but then eat a surplus of 1250 on both days of the weekend (a total surplus of 2500 calories), your 2-day surplus has cancelled out your 5-day deficit and you have now averaged the week at maintenance, meaning your weight will stay the same.

If the blow-out weekend surplus of 2500 calories sounds a lot, consider spending just one evening in Pizza Express:

  • Lemon & herb chicken wings starter: 556 cals
  • Padana pizza for main: 1108 cals
  • Red berry & vanilla cheesecake dessert: 552 cals
  • 2 x medium glasses (175ml) of red wine: 320 cals
  • One night out at Pizza Express = 2536 calories
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Conclusion – why your calorie deficit isn’t working

The basic laws of physics say you must be in a sustained calorie deficit to lose weight. If you do not lose weight then, whatever you might think, whatever your calculator, fitness tracker, scales or app say, however much exercise you think you are doing, you are not in a calorie deficit and you must reduce consumption further and/or increase activity for weight-loss to occur.

A DEXA scan will provide a very good starting point for your weight-loss journey because it will measure your body composition accurately and give you a very good idea of how much fat you could lose, a realistic calorie deficit below maintenance and how long it will take to reach your goal.

Bodyscan’s DEXA scan consultants will give you the best advice on how to practically achieve lower fat and a healthier body, so get in touch today.

Philip Chant
Bodyscan Director


In this article, we have emphasised weight-loss over fat-loss, though of course, almost everybody wants/needs to lose fat, not weight (ie, you do not ordinarily want or intend to lose muscle mass). While it is true that you must be in a calorie (energy) deficit to lose weight (body mass), it is possible to lose body fat without being in a deficit. Specifically, if you eat at maintenance and gain muscle mass through an optimised resistance programme, then you must necessarily lose fat at the same time because at maintenance your weight must stay the same. This is true body recomposition and, in this example, you lose body fat without being in a calorie deficit. This approach is only suitable for those with relatively low levels of body fat to start with because muscle-gain is usually slower than fat-loss.