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Finding a kcal deficit that works for you.

Finding a kcal deficit that works for you.

If you you are looking to lose weight, we know that you need to burn off more kcals than you eat, but how do you find an appropriate kcal deficit for you? Cutting kcals too low can effect mood, health, performance and ultimately lead to failure. Not cutting kcals enough means you don't see any results! This blog post goes through the steps that you can take.

One of the biggest frustrations I hear from clients, is that they know about a kcal deficit, but don't really know how to action it properly.

And so called experts aren't always helpful. All you have to do is look around social media and you'll get the same sort of advice:

"Every diet that works gets you in a kcal deficit"

"You can't deny thermodynamics"

"Energy in vs energy out, that's all you need to know"

"If you eat in a kcal deficit you'll lose weight"

"If you're not losing weight then you're not in a kcal deficit"

"Kcal f*cking deficit".

"It's really simple, just eat less than you consume"

"Eat in an appropriate kcal deficit"

OK, but what's my 'appropriate' kcal deficit, how many calories/how much food should I actually eat?.

It starts by knowing your metabolic rate.

1. What is your metabolic rate?

Your resting metabolic rate is the amount of energy that your body needs to function and maintain itself.

The Basal Metabolic Rate (BMR), also known as the Resting Metabolic Rate (RMR), is the largest portion of how many kcals you burn in a day (around 60%) and is key if you want to calculate if you're in an energy deficit. As a result, accurately estimating RMR is critical for creating a successful weight loss plan (1). If you know how many kcals you burn at rest, you can then figure out how many kcals you need to lose weight.

How to measure your metabolic rate

The only real way to establish your resting metabolic rate is through metabolic testing or a Resting Metabolic Rate (RMR) Test.

The other option is to use kcal calculators you can find online (even I have one!), however, even if we account for your age, age, height and weight, these calculators can still be wildly inaccurate. We know that weight, waist to hip ratio, previous diet history and fat free mass all affect the reliability of these equations (2). The more accurate calculators are still only right 50% of the time!


Ignite By Box Nutrition and Performance is a weight loss programme that provides you with a plan based on you as an individual. If you're sick of trying to figure this puzzle out by yourself, then find out how we can help.


2. Creating your deficit

Now that you've got your RMR, you now need to create an appropriate deficit. This is another area that can leads to problems. People often use arbitrary deficits like 500kcals, however your deficit should reflect you as an individual and your needs. Taking 500kcals off an RMR of 1200kcal will not be a good idea!

Things you need to account for:

  1. Your unstructured activity - how many steps do you do?

  2. Your structured activity - what type of exercise are you doing? How many kcals/carbohydrates does it require?

  3. What is your time frame? How quickly do you want to lose weight?

  4. The size of your deficit - are you creating a deficit relative to your weight and body composition

3. Tracking your food (not forever!)

Once you have your kcal targets, use an app like MyFitnessPal or Chronometer to record what you eat. My advice is to eat normally start with, which will highlight where you are in relation to your kcal targets. Then it's just a case of adjusting what you're eating. This also helps you begin to understand food values and how best to put together your meals. Over time, when you begin to understand what a 500kcal meal looks like, or how to get 20g of protein you can begin to move away from tracking and use more of an intuitive approach.

4. Be willing to adjust

Even if you get metabolic testing, you need to be willing to adjust what you eat moving forward. As you lose weight your metabolic rate may slow down, it may increase as you get fitter or, a change in activity might mean you need more carbohydrates. This is why you need to use cues like hunger, energy levels and your results to tweak your plan. If you find that you're really hungry then increase your food by 150kcals a day, if after 3 weeks you're not seeing any results then reduce your food intake by 150kcals per day.

How we can help?

I appreciate the above can still seem confusing. This is why we have put together Ignite, the weight loss programme which uses clinically validated testing to build a plan specifically around you and your individual needs. What you get.

An appropriate kcal deficit based on you

Through metabolic testing we can accurately measure how many kcals you're burning at rest. This means it's easy to provide you with a kcal deficit which is based on YOU. That's not too low so you're not starving, but also low enough that you see results.

This gives you some objective and accurate data to use, but also a bit of peace of mind that what you are doing is working.

Kcal and macronutrient targets adjusted to your goals

As well as providing you with a set of kcals, we also know that having an understanding of what to actually eat is incredibly important.

This is why we also give you a macronutrient breakdown (protein, carbohydrates, fat) based on your body composition, activity and previous diet history. By measuring your lean muscle mass we can accurately calculate your protein need. Basing your protein targets off weight is inaccurate as body fat does not need protein like your muscles.

Portion guide based on your data

You also receive a portion guide and meal builder based on your kcals and macronutrient targets. This tells you how big your portions should be, how many portions you need per day and how to put wholesome and nutritious meals together.

A full report and debrief session

I pride myself on making sure you understand what you need to do to continue to see results. This is why you also receive a full report and debrief session with me going through your plan so you know exactly what you need to work on moving forward.

Fat burn test

Maximise your results and consider our fat burning testing. This measures how many kcals you burn during activity as well as what your fat burning rates are like. We can then provide you specific exercise sessions to help with both fat loss and fitness based on your needs.

If you're interested in signing up then get register your interest here to arrange a chat to see if you're right for the programme, or find out more about Ignite and book here. You can also use our macro calculator for to work out your kcal and macro needs.


  2. Article Accuracy and Validity of Resting Energy Expenditure Predictive Equations in Middle-Aged Adults


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