How Much Body Fat Can You Lose In a Week?

14 September 2022
By Jack Coxall

For most people, a weight loss goal will often look like “as much as possible, as quickly as possible!” – but, despite good intentions, this isn’t always realistic or healthy.

So, how much weight to lose in a week is realistic, healthy AND sustainable?

In this article, we’ll take an in-depth look at the maths surrounding calories and body fat % – as well as calling out some low hanging fruit that you may not be reaching right now that has the potential to help you reach your goals faster.

How much body fat can you lose in a week?

In order to lose body fat we have to be in a calorie deficit. That means we have to expend more energy in the day than we consume.

However we are not robots – and various day-to-day and bodily functions can affect our energy balance.

The more energy you expend in the day exercising, walking, fidgeting, playing with your children, taking the stairs instead of lifts and just moving in general will help. However the amount of calories you consume in the day still needs to be less than this, consistently, in order to lose weight. 

Losing body fat and weight loss are not the same thing. The number on a weighing scale can be affected by water retention, muscle mass, alcohol intake, hormones and medication – to name just a few.

You could be losing body fat but not ‘losing any weight’ as the number on the scale stays the same. If you had a particularly salty meal your water retention would be higher and therefore a potentially higher number on the scale and if you have remained in your calorie deficit consistently it is unlikely to be body fat. When we start out on a weight loss journey, it is body fat that you would be looking to reduce – so it’s vital we are using a body fat scanner to measure our progress and not just weighing scales. 

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Water makes up 60% of your body weight and it’s one of the first things you’ll lose when starting out on your weight loss journey. If your weight is fluctuating a lot and you are losing a significant amount of weight in a short space of time, this is likely to be water weight that you are losing. If the weight is coming off more slowly and you are being consistent with your training and diet and you are fitting into smaller clothes and looking leaner, it is more likely to be body fat that you are losing. 

Trying to lose as much body fat in a week as possible is only going to be detrimental to your health in the long run. Sustainability is key – with both exercise and diet to achieve the results you want.

How fast can you lose body fat and stay healthy?

You can lose a significant amount of body fat quickly, however you would also lose a large amount of muscle mass, you would be extremely fatigued and hungry and your immune system would potentially be shot to pieces.

This significant body fat decrease therefore would not be sustainable and you would likely be back to your original habits and lifestyle and back to square one pretty quickly. To lose body fat and stay healthy, a slight calorie deficit is required in order for you to keep up your energy expenditure levels. By dropping your calories too low, you naturally don’t move as much and therefore expend as many calories. So a lose lose all round – and you’ve eaten less for no reason.

A calorie deficit of around 500kcals a day would be -3500kcals across a week. -3500 kcals is the equivalent of -1lb/-0.5kg of body fat loss a week. This is sustainable and would not cause fatigue or a significant loss in muscle mass or energy expenditure either. It can be achieved by making small but significant changes to your day to day nutrition rather than a huge overhaul. A reduction in portion sizes and an increase in vegetables just to name a few. If you were to be in a deficit of more than this every day, it would not last very long. Motivation would maybe keep you going for a few weeks but then hunger and fatigue would take over.

It’s definitely healthier to lose 1lb of body a week consistently for say 52 weeks than try and lose 3-4lbs a week and only last 4 weeks before giving up and ending up at square one back in your old habits and even less motivation. Slow and steady wins the race when it comes to fat loss. It didn’t all go on in 2 weeks, so it certainly won’t come off in 2 weeks. 

How long does it take to lose 1% body fat?

1% of body fat is going to be different for everyone depending on your starting body fat %.

Like I said above, -3500kcal deficit is the equivalent of losing 1lb/0.5kg of body fat a week if you’re in a 500kcal deficit daily. However if your body fat % and weight are particularly high to begin with, results are likely to be faster at the start as a heavier person moving an equal distance, or an equal weight object moved a greater distance will require more work to be accomplished. Work is energy and even a steady walk will expend more energy for a person carrying a higher body fat %.

When starting out with any exercise programme, especially as a beginner, it is possible to increase muscle mass and decrease body fat at the same time. The more muscle we have, the more calories we burn at rest (BMR). So as we increase muscle mass and remain in a calorie deficit, it may be that we are in a larger deficit as we go.

This doesn’t continue forever though. If you are in too much of a calorie deficit and you become proficient with movement and exercise we can find it hard to maintain muscle mass.

So finding that balance is key. More muscle = more food can be consumed without heading into a surplus. Very ideal.

How long to lose 10% body fat?

The more sustainable and attainable your lifestyle, diet and exercise choices are the quicker you will reach a target of losing 10% bodyfat.

Again, if your bodyfat % is high to begin with, this will be faster than if it is lower. Usually because someone with a higher body fat % can make a lot more changes in a shorter space of time regarding their day to day, diet and exercise choices. They have more changes to make to reverse the increase in body fat % that would have happened over a long period.

Someone with an average body fat % wanting to lose 10% body fat will find it difficult as they are currently already making the relatively correct lifestyle, diet and exercise choices. Just small tweaks would be needed but progress would be slower.  

What kind of average body fat % loss per month should I aim for?

Body composition is affected by so many different variables that an expectation to lose 1-3% of body fat a month is achievable.

However like anything in life this drastically varies from person to person depending on starting %, gender, muscle mass and lifestyle. There are no standards or guidelines for how quickly to lose body fat or gain muscle because there hasn’t been enough research to determine what a healthy body fat % should be.

We all have very different lifestyles, so as long as any changes we make are achievable and sustainable for us individually we are heading in the right direction. Someone with an active job may struggle less to lose weight compared to someone with a 9-5 high stress desk job. The key is finding what works for you and if that means banking calories in the week so you can enjoy your weekends, reducing portion sizes or taking the dogs for a slightly longer walk on weekends then that is great. 

Going too fast too quickly will only end in disaster. Noone wants to feel hungry, fatigued or irritable. Slow and steady wins the race.

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