Counting calories – or being in a ‘calorie deficit’ – is a traditional approach to weight loss that’s found a new audience and a popularity boost on social media.


Simply put, a calorie deficit is when you eat fewer calories than you burn off. It’s the age-old principle behind many weight loss plans – use more calories than you eat and you create a shortfall, the body then has to turn to its own fuel stores for energy.

The key question is, does this age-old approach to weight loss really help you reach and, more importantly, stick to your weight loss goals?

How do you create a calorie deficit?

It is possible to create a deficit both by increasing the amount of physical activity you do and by reducing the amount of food you eat. Studies suggest the best way to achieve weight loss and, more importantly, maintain it, is to do a combination of these two – decrease your calorie intake and increase your expenditure, through physical activity.

How do I know how many calories I need?

The number of calories we need varies for each and every one of us. Our age, gender, build (including height, weight and muscle mass), activity levels and our general state of health and genetics all determine our calorie needs.

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How does my body burn calories?

Your body converts the food and drink you consume into energy by a process called metabolism. Through a series of chemical reactions, calories are combined with oxygen to form energy. Even at rest we need calories to fuel our breathing, keep our blood pumping, maintain hormone and blood sugar balance, and for growth and repair.

The number of calories we need when we are at rest is called our basal metabolic rate and is the minimum number we need before we add any activity to our day and before we take into account the energy required to digest our food and keep ourselves warm.

How do I calculate a calorie deficit?

Bowls of tasty and healthy looking salads

First you need to know your daily calorie requirements: there are a number of online calculators that claim to help you with this. These calculators predict your energy needs based on the information you provide: this typically includes your gender, height, weight, age and activity levels. Sadly, these calculators cannot calculate with any degree of accuracy because there are many more variables that influence your calorie needs, including how muscular you are. What this means is, the figure the calculator gives you may be several hundred calories higher or lower than your actual maintenance needs so it is best to treat this figure as a guide only.

UK guidelines suggest that for a gradual, safe weight loss a calorie deficit of 500-600kcal per day is needed. Deduct this figure from your estimated maintenance needs to arrive at your weight loss calorie target for the day.

Other online calculators and apps may help you assess your calorie intake, based on the food you log, and your calorie expenditure, although studies suggest a fitness watch may provide a more accurate assessment of your actual energy used.

Online resources included are for information purposes, their inclusion does not constitute or imply an endorsement or recommendation.

Will following a calorie deficit help me lose weight?

As science advances, we’re beginning to appreciate that the theory of ‘calories in and calories out’ may be an over-simplification of the way our body uses energy. Like most processes in the body, energy use, expenditure and storage are all tightly controlled. This means the body strives to maintain a constant store of energy, so when it detects an energy shortfall it compensates by reducing the energy it uses, effectively slowing your metabolism. This maintains your energy stores at a fairly constant level.

There may also be other factors at play including the type of foods you eat, how it was processed and prepared, what combination of foods you enjoy, and even the type and variety of bacteria that live in your gut.

If you regularly enjoy a handful of nuts, such as almonds, you may already be benefiting from these factors. That’s because nuts and other plant foods have fibrous cell walls that our digestive enzymes can’t always break down, this means we are not able to access all of their contents, including some of their calories. However, if we were to eat nuts after they had been processed, such as ground almonds, we would access more of their nutrients and more of their calories.

Is a calorie deficit healthy?

Your body needs a minimum number of calories to function properly, and in addition to this it needs a wide range of nutrients to maintain health and support growth and repair. Not getting enough of these nutrients may put your bones at risk, deprive your brain of important energy, disrupt hormonal balance, leave you tired and put you at risk of other health conditions, including gallstones.

However, if you do enjoy a nutritionally adequate diet, while restricting calories, then you may experience benefits beyond that of weight loss. Studies suggest calorie restriction and fasting may increase your longevity and may reduce your risk of type II diabetes, heart disease and cancer.

Therefore, if you adopt the calorie deficit approach, be sure to focus on the quality of your diet and include plenty of nutrient-dense foods in line with current dietary guidelines.

A nutritionist’s view

We obtain calories from the macronutrients we eat – these include proteins, carbs and fats, as well as alcohol. Whether we absorb all of these calories depends both on the food we eat, how it was prepared and processed, and its individual characteristics. In addition to this our gut bacteria may influence how we absorb, use and expend the energy we eat. There’s still much for us to learn in this area and conclusive evidence is lacking but it does suggest our weight loss journey may be more individual than we first thought.

That said, a calorie deficit approach may be a useful way to kick-start your weight loss, but expect your weight to plateau after a few months. Should you experience this, try to incorporate more activity into your day, consider your meal timings, think about enjoying a higher calorie breakfast and ensure you have an overnight fast.

Overall, is a calorie deficit approach effective for weight loss?

It can be a helpful way to get your weight loss journey started, but don’t expect a calorie deficit to solve your weight loss issues. In the long-term this approach is not a sustainable way to lose weight, and keep it off, because the body adapts to the reduced energy intake. Consistently restricting your calories is likely to leave you hungry and if all you focus is on are the calories on your plate, you’re also likely to miss out on the well-balanced diet that will help secure your long-term health and fitness. Unfortunately, there is no single best strategy for weight loss and maintenance, and success will depend on you finding the best approach for your own individual circumstances and preferences.

Top of an open can of drink. Text at the top of the can reads 'No sugar, no calories'

As with all diets, pregnant and breastfeeding women as well as diabetics on medication, should seek medical advice before embarking on a restricted eating programme. This sort of eating plan may be unsafe for teenagers and children, who are likely to miss out on crucial nutrients needed for growth. Please refer to your GP or a registered dietician for further guidance.

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All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other healthcare professional. If you have any concerns about your general health, you should contact your local healthcare provider. See our website terms and conditions for more information.

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