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If you want a quick answer, the average person should be aiming to lose between 1-2% of their body weight per week. This means an 80kg person would need to be in a deficit for 10 weeks (2.5 months) to lose 10% of their body weight, i.e. 8kg (provided they lost 1% of their body weight per week).
THE SIZE OF THE DEFICIT DEPENDS ON THE AMOUNT OF DESIRED WEIGHT LOSS
We all know that you need to be in a calorie deficit to lose weight.
That means you need to be eating fewer calories than you use over a long enough time period to drop the amount of weight you want to drop.
But how long is long enough, and how long is too long?
Well, it all depends on exactly how much weight you want to lose.
Put it this way, if you are only in a calorie deficit for one day, you’re not gonna lose much weight.
Let’s say you use 2,000 calories per day, and you eat 1,800 calories.
This gives you a deficit of 200 calories.
Given that a Kg of fat contains around 7,700 calories (1lb contains 3,500 calories), if you’re in a 200 calorie deficit per day, it’d take 39 days to lose 1kg or 18 days to lose 1lb…
That means if you want to lose 10kg (22lbs) it would take you 385 days to lose it if you were only in a 200 calorie deficit per day!
That’s over a year!
Your progress would be so slow you’d probably get demotivated and quit after a few weeks.
Let’s say on the other hand that you used a deficit of 500 calories per day. If you did this, you’d lose 10kg in 154 days, or about 6 months.
This is much more realistic, easier to stick to, and will produce a good amount of loss in less time.
But let’s say you wanted to go even faster…
You could be in a 1,000 calorie deficit per day. If you stick to that, you could lose 10kg in 77 days or just 2.5 months… Not bad!
So, as you can see, the bigger deficit you’re in, the quicker you’ll lose weight. The downside is, that bigger deficits are harder to stick to and require more sacrifice.
The chart below shows roughly how long it would take to lose 5, 10, 15, 20, 25, and 30kg based on different sizes of calorie deficit.
CALORIE DEFICIT TIMEFRAME CHART
|100kcal||385 days||770 days||1155 days||1540 days||1925 days||2310 days|
|200kcal||193 days||385 days||578 days||770 days||963 days||1155 days|
|300kcal||128 days||257 days||385 days||513 days||642 days||770 days|
|400kcal||96 days||193 days||289 days||385 days||481 days||578 days|
|500kcal||77 days||154 days||231 days||308 days||385 days||462 days|
|600kcal||64 days||128 days||193 days||257 days||321 days||385 days|
|700kcal||55 days||110 days||165 days||220 days||275 days||330 days|
|800kcal||48 days||96 days||144 days||193 days||241 days||289 days|
|900kcal||43 days||86 days||128 days||171 days||214 days||257 days|
|1000kcal||39 days||77 days||116 days||154 days||193 days||231 days|
As you can see, the larger the amount of weight you want to lose, the bigger deficit you need to be in if you want to lose that weight in a reasonable time frame.
So, if you wanted to lose 5kg and you were only in a 100 calorie deficit per day, it would take you over a year to achieve it.
That rate of loss is so slow that most people would just give up.
At the same time, a 1,000 calorie deficit per day would mean you’d lose 5kg in just over a month, but for more people, it would be way too aggressive and restrictive.
For example, a moderately active 30-year-old female weighing 75kg might burn around 2,000 calories per day. So, in order to lose 5kg in a month, she’d need to eat roughly 1,000 calorie diet on a daily basis. While that is doable, it would require a LOT of willpower and sacrifice.
So, the answer lies somewhere in the middle.
A 500 calorie deficit per day means losing around 0.5kg per week, losing the desired 5kg in 77 days, or around 10 weeks (2.5 months).
For most people, this is a good balance because it means you’ll see enough progression the scales and in the mirror to keep you motivated, but the diet won’t need to be super restrictive or low calorie.
That would mean that our 75kg female would need to eat 1,500 calories per day.
This may still sound quite low but do consider that it doesn’t need to be 1,500 calories every single day..
But rather, 1,500 calories on average
If this person liked eating more at the weekend they could organize their week like this;
This means that by eating low calories on Tuesdays, Wednesdays and Thursdays, this person could afford to eat 3,700 calories on Saturday; that’s a lot of calories!
Of course, if someone had a lot more weight to lose, it’d take a lot longer to lose.
Let’s say for example you wanted to lose 30kg.
If you only had a 100 calorie deficit per day it would take you 2,310 days. That’s six years.
When you can’t even see the light at the end of the tunnel you’re going to have zero motivation, so aiming for a 100 calorie deficit is just not practical if you want to lose 30kg.
If you were in a 1,000 calorie deficit, however, losing 30kg would take 231 days or around 8 months.
Losing 30kg would totally transform your physique, your health and your entire life and 8 months of consistency and dedication doesn’t sound like a bad trade for that.
The good news is, if you weighed 30kg, your metabolism would be much higher, so you’d be able to diet on relatively high calories.
For example, if you were a moderately active male weighing 130kg you could diet on around 2,500 calories and lose that 30kg in 8 months.
So, as you can see the amount of time you spend in a deficit will depend on how much weight you want to lose, and how big of a deficit you’re prepared to be in.
HOW LONG CAN YOU STAY IN A CALORIE DEFICIT FOR?
This is a totally different question.
You can of course stay in a deficit indefinitely but I’ll give you a second to guess what would happen…
No? Well, you’d die.
Yep, if you stayed in a deficit for long enough you’d eventually lose so much body fat and muscle tissue that you’d have almost none left, and your body would start to cannibalize your organs.
Of course, that’s extremely unlikely to happen unless you suffer with a severe eating disorder.
At some point, you’d reach a bodyweight ‘set point’ where you’ll find it very difficult to lose weight, but the amount of time you can stay in a deficit for will probably correspond very closely with how long you should stay in a deficit for.
Just a quick time out, if you want to work out your calorie now, just use the tool below[cal_calc]
CAN YOU LOSE MUSCLE IF YOU STAY IN A DEFICIT TOO LONG?
The simple answer is yes. The longer you’re in a deficit, the more your body will use stored body fat as fuel in the absence of calories.
This is how fat loss works – the fat on your body is used to provide energy, therefore making you lose weight and look leaner.
But your body will want to hold onto at least a little body fat, so if you carry on in a calorie deficit for too long, your body will start to burn muscle as well as fat.
You might think that you don’t care about that, but you should.
Everybody should want to hold on to as much muscle as possible, regardless of whether you’re a bodybuilder competing in the Arnold classic, a stay-at-home mum of 2, or a retired 75-year-old.
Well, muscle has a ton of benefits, including;
- It’ll make you look better. Yep, muscle is what gives you shape; if you’re a guy you probably want wide shoulders and a wide back. If you’re a girl, you might want bigger glutes. Muscle is what will give you those things
- The more muscle you have, the higher your metabolism will be. This means you’ll be able to eat more calories to maintain your weight or lose weight. And who doesn;t want that?!
- More muscle will make you stronger which will make day to day activities like DIY, carrying shopping and just lifting stuff will be easier
- If you play a sport, the chances are that more muscle will make you faster, more powerful and generally better at that sport.
So, muscle = good.
The problem is the longer you’re in a deficit for, and the more aggressive the deficit is; the more muscle you could lose.
The good news is that muscle loss can be avoided by using certain strategies. Thus study suggested that both a higher protein intake and resistance training can minimize the amount of muscle loss that occurs in a calorie deficit.
The study suggests that an intake of 1.2g of protein per Kg of bodyweight is optimal. This means someone weighing 80kg should eat around 96g of protein per day. Resistance training makes perfect sense for muscle preservation; if you’re constantly using your muscles, you’re giving your body a signal that you need to hold on to whatever you have.
So, the key takeaway here is, if you are dieting and you don’t want to lose lean body mass (muscle), resistance train and eat more protein!
WHAT ARE THE HEALTH RISKS OF BEING IN A CALORIE DEFICIT FOR TOO LONG?
While muscle loss is a risk factor, there are other negative side effects that can arise from long protracted periods of weight loss.
These include (but are not limited to);
- Poor sleep
- Limited ability to concentrate/focus
- Reduced sex drive
- Less overall energy which can affect your workouts
- Less cope to enjoy food/socialize
- Potential muscle loss
- Reduced metabolism
Of course, none of these things are life-threatening, so if you are laser-focused on your weight loss goal you could just push through and deal with some or all of these negative side effects.
The issue is, the longer you do this, the more of a problem some of these side effects will become, and some of them could even undermine your weight loss goals.
Let’s take the problem of low energy as an example.
If your energy is low your motivation to work out (or even move in general) will decrease.This means that if you follow your body’s natural instinct to move less, you’ll be burning fewer calories each day.
This may mean that you’re no longer in a calorie deficit.
In this situation, eating a little more to fuel your workouts could give you a better net result (i.e. keep you in a calorie deficit.
Plus, exercise is obviously beneficial outside of just weight loss, so stopping altogether just because your energy is low is going to be counterproductive in the long run.
If you do plan to be in a calorie deficit for a long time however, there are tactics you can use to limit any harmful side effects and generally make the entire process of weight loss easier for yourself.
Enter diet breaks…
SHOULD YOU EVER TAKE A BREAK FROM YOUR CALORIE DEFICIT?
A diet break is a pre-planned period of time where you take yourself out of a calorie deficit.
Rather than eating in a deficit, you’d eat at maintenance calories for 1-2 weeks. In this period, your goal should be to simply maintain whatever your current weight is.
Taking a diet break will mean it takes longer to reach your desired weight, so why would you do it?
Well, diet breaks have both physiological and psychological benefits.
From a physiological standpoint, taking regular diet breaks can mitigate a lot of the unwanted negative side effects mentioned above.
The mental aspect is arguably more important, however.
Staying in a deficit for long periods of time can be taxing, taking a 1-2 break can allow you to eat a little more, train a bit harder in the gym and relax a little.
Yes, it will mean the diet takes longer overall, but that’s better than never reaching your goal at all because you quit.
Let’s use the example of a 100kg person wanting to lose 30kg. If they were to use a deficit of 800 calories, they’d be looking at around 289 days. 800 calories is a fairly aggressive deficit however, so keeping that up for 10 months is going to be tricky.
This is a scenario where diet breaks would help you out. 10 months is 40 weeks, so if you were to take a diet break every 4 weeks, you’d extend the diet by roughly 10 weeks. While this is a 25% increase, it would hugely increase the likelihood of the diet being successful.
You may not like the sound of a diet that lasts pretty much a whole year, but it’s far better to be realistic about the timeframe and actually achieve your goal rather than to tell yourself you can achieve it in the shortest possible time frame then give up a few months in because it’s too difficult.
So to summarize, the bottom line is
- How long you ‘should’ stay in a calorie deficit for really depends on how much weight you want to lose and how aggressively you’re prepared to diet. The bigger the deficit is, the sooner you’ll hit your target, but the more difficult it will be
- Don’t always go for the quickest option, i.e. the biggest deficit. Of course, we all want to lose weight as quickly as possible, but if you go too aggressive on your diet, you’ll end up quitting altogether and getting into an endless cycle of yo yo dieting.
- Aim to lose between 0.5-1.5% of your body weight per week. That means, if you weigh 80kg, you should be looking to lose between 0.4kg–1.2kg per week
- If you plan to be in a deficit for a long time (12+ weeks), ensure you take regular diet breaks to give you physiological and psychological respite
Weight Loss Strategies and the Risk of Skeletal Muscle Mass Loss: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8308821/