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How Much Should I Eat To Lose Weight?

When it comes to losing fat, there is no one-size-fits-all answer. How much you need to eat depends on a number of factors, including your metabolism and how active you are.

But how many calories should you eat if you're looking to lose fat? This blog post will answer this questions.

Losing weight is all about creating a calorie deficit. That means you need to be eating fewer calories than your body is burning off each day. But even though this may seem simple. Why is it that it can be so difficult to get right.

The two main reasons are:

  1. The deficit is too large which can down-regulate your metabolism, lead to muscle loss and most importantly making it unsustainable

  2. The deficit is too small meaning resulting in no change

OK so how should you calculate how many calories should you be eating.

Step 1 - Figure out your Resting Metabolic Rate

Your Resting Metabolic Rate is the number of calories your body burns at rest. This is the amount of energy your body needs just to keep all its systems functioning when you're not doing anything.

To get your RMR, you can get an RMR test which is the only accurate method, or you can estimate it.

You can estimate your RMR using any calculator online, however be aware these calculations are an estimate. I personally like to use the Katch McArdle Formula for those who are active as it looks at lean body body mass rather just weight.

The Katch McArdle Formula:

RMRCalc = 370 + (21.6 x LBM)

LBM is your Lean Body Mass in kilograms so if you weigh 80kg and have 20% body fat, your LBM would be 64kg (80 x 0.8).

So using the Katch McArdle Formula, if I weigh 80kg and have 20% body fat, my RMR would be 1752calories.

If you're not very active (desk job, exercise less than 3 x per week) I'd use this number as your starting point, however if you are active I'd add an extra 10-20%.

  • 10% - Calories = 1752 x 1.1 = 1927

  • 15% - Calories = 1752 x 1.15 = 2014

  • 20% - Calories = 1752 x 1.2 = 2102

Step 2 - Calculate your rate of weight loss

The next step is to calculate how fast you want to lose weight. This is important because you need to create a sustainable calorie deficit that will allow you continuous weight loss without too much muscle loss and metabolism down regulation.

In a previous article we discussed how a good starting point for most people is 0.5-1% of your body weight. So if you weigh 80kg, you should be looking at rate if weight loss of 0.4-0.8kg per week.

0.5% of 80kg = 0.4kg

1% of 80kg = 0.8kg

Studies also show that individuals with a higher body fat % will see quicker results to begin with. To account for this you can estimate your target weight loss rate by dividing your current body fat % by 20. Using our 80kg example who is 20% body fat, their target rate of weight loss would be 1kg per week.

(20/20) = 1kg

If an individual was 90kg with a body fat % of 45%. heir target rate of weight loss would be 2.25kg per week.

(45/20) = 2.25kg

If you're unsure of your body fat %, use the Navy method here to estimate yours.

The problem here is that again it's coming down to estimations, which is why metabolic and body composition testing can really help understand how much you should be eating for your weight loss goals.

Step 3 - Implement and Adapt

So now we've figured out how many calories we should be eating (our RMR) and how fast we want to lose weight (our target rate), we need to implement this into our lives.

The best way to do this is by tracking your calories and weight loss progress over time. I would recommend doing this for at least 2 weeks, but 4-8 weeks is ideal as you'll get a better understanding of how your body responds.


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There are a few different ways you can track your calories, but the simplest method is by using an app like MyFitnessPal.

Once you have an understanding of how many calories you should be eating and how quickly you want to lose weight, it's time to start making changes.

If after 2 weeks you're not seeing any weight loss, then I would recommend reducing your calories by 10% of your calories per day. Alternatively, if you're losing weight too quickly (more than 1kg per week) then you can increase your calories by the same amount.

What about extra activity?

A question I'm often asked is how do you adjust your calories in MyFitnessPal when you exercise. "Should I eat the calories back I burn from exercise?".

The short answer is no.

The reason being is that:

  1. Research has shown that your watch/phone are not very accurate when estimating your calorie burn, where they can be off by up to 20%! So if you eat these calories back, you would no longer be in a calorie deficit.

  2. For the time when you would be exercising, you would still be burning calories if you were at rest. So let's say you burned 400 calories in the gym in 60mins, as you would be burning around 100 calories at rest if you hadn't exercised, that's only an additional 300 calories above what we have calculated from your RMR. 400 - 100 = 300 calories. Eating the 400 would again cut into your calorie deficit.

  3. Your metabolic rate can slow down after you exercise. Research has shown that exercising hard can actually lead to a down-regulation of your metabolic rate after you train. So if you exercise hard, how many calories you burn for the rest of the day may actually come down.

These 3 reasons are why I wouldn't eat back your exercise calories if weight loss if your goal.

The only exception to this rue is if you are doing very high amounts of exercise (90mins + hours per day). In this case, you would need to increase your calories to make sure you're not under eating. In these scenarios, you may wish to eat back 50 or 75% of the calories you have burned still ensuring you're in a calorie deficit.

To Sum Up

When it comes to losing weight, there's no one-size-fits -all solution, which is why the best way to find out how many calories you should be eating is through testing, as we all have different metabolism's and body types. However, this is only the first step in succeeding with your weight loss goals. Once you have your calorie target, it's important to monitor your weight loss rates and adapt your eating based on your progress.

To find out more about how to do this, check out our signature weight loss programme, Ignite, which combines metabolism and body composition testing with nutrition and exercise support to guarantee weight loss. Find out more about our weight loss programme here, or get in touch to see what options are best for you here.


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