How Much of a Calorie Deficit is Too Much?

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Joe is an online weight loss coach and qualified personal trainer of 15 years who helps busy, professional men and women lose fat and build muscle.

Having a 9-5 desk-job, Joe understands the struggles of juggling a hectic life with trying to maintain a good physique.

If you want to know more, check out the about page, or get in touch

Yes, of course, we all want to lose weight as quickly as we possibly can 

I mean, Why Wouldn’t you?

Who in their right mind thinks ‘wouldn’t it be great to get to my goal as slowly as possible?

Unfornatutely, like many other things in life, if you want to do weight loss the right way, it takes time.

But ‘how low can you actually go with your calorie deficit isn’t really the question, what you should be asking is how low should you go?

Yes, ultra-fast weight loss is possible, but just because it’s possible doesn’t mean you should do it

How Calorie Deficits Work 📉

A calorie deficit is a state where you’re eating fewer calories than you use, on a daily basis, over a long period of time.

If you eat fewer calories than you need, your body will use stored body fat to make up for the shortfall in energy.

This is what will gradually make you lose body fat, and overall body weight over time.

In theory, it doesn’t matter what you eat, as long as you’re in a calorie deficit

The size of the calorie deficit will determine how quickly you lose weight, for example, if you use 2,500 calories per day (on average), and you eat 2,000 calories a day (on average), you’ll be in a 500 calorie deficit, meaning you’ll lose roughly 0.5kg or 1lb per week.

The larger the deficit, the quicker you’ll lose weight, but the harder it’ll be to maintain.

drake weight loss meme

The goal for the vast majority of people should be to pick a moderate, healthy calorie deficit that you can maintain easily for several months, without feeling extreme hunger or suffering in any big impacts on other areas of your life.

How Quickly You’ll Lose Weight on Different Sizes of Deficit ↔️

So, as you’ve learned (yes, I hope you’re taking notes at the back), bigger calorie deficits will result in faster weight loss.

Below is a quick guide to show you how much weight you’d lose per week and per month (on average) with different sizes of deficit in Kg…

Size of DeficitWeekly Weight LossMonthly Weight Loss
250 Calories0.2kg0.8kg
500 Calories0.5kg2kg
750 Calories0.75kg3kg
1000 Calories1kg4kg
1500 Calories1.5kg6kg

And in pounds for our friends across the pond…

Size of DeficitWeekly Weight LossMonthly Weight Loss
250 Calories0.5lb2lb
500 Calories1lb4lb
750 Calories1.5lb6lb
1000 Calories2lb8lb
1500 Calories3lb12lb

On the graph below, you can see what these different sizes of deficit actually look like over time.

The different colored lines represent different sizes of calorie deficits.

This essentially shows the different speeds at which a 100kg (220lb) person would lose weight using different sizes of the deficit over 12 weeks

The blue line shows how quickly they’d lose weight in a 250-calorie deficit, while the orange line show’s how fast they’d lose weight in a 1,500 calorie deficit.

different sizes of calorie deficit graph

It probably won’t surprise you to learn that using a 250-calorie deficit, this person would lose around 3kg (6lbs) over 12 weeks

With a 1,500 calorie deficit, however, this person would lose 16.5kg (33lbs).

That’s over 5 times as much weight in the time period, so why the hell wouldn’t you just go for a huge deficit, and get all the weight off as quickly as possible?

How Much of a Calorie Deficit Is Too Much? 😥

Although extreme weight loss sounds great, in reality, large calorie deficits are going to be incredibly difficult to maintain for any significant amount of time.

Why?

Well, eating very low calories is just bloody difficult.

Think of it this way; the average, moderately active person will probably use around 2,500 calories per day.

So, if that person wanted to eat in a 500-calorie deficit, they’d be eating 2,000 calories per day, which is more than manageable for most people.

If that person wanted to eat in a 1,500 calorie deficit however, they’d need to eat 1,000 calories a day 

Even with all the motivation and willpower in the world, eating 1,000 calories a day continuously is extremely difficult and would be almost impossible for the average person to stick to long term

Of course, it’s possible but it would mean making a LOT of sacrifices, including the likes of;

  • Take out meals
  • Dinners out
  • Nights out (and dinks)
  • Holidays
  • Work events
  • Weddings
  • Calorie dense snacks

While holidays and weddings can be done without overindulging, it’s incredibly tricky and will probably involve lots of explaining yourself to other people 

“Go on, have a drink”

“I can’t, I’m trying to maintain a 1,500 calorie deficit” will probably get you a few funny looks

OR you just won’t enjoy the day/week/fortnight as much as you could have, in which case, what’s the point, right?

For this reason, a 1,500, and even a 1,000 calorie deficit are probably too much for most regular people to maintain.

Even knowing all of that, some people still think they can do it, and this ends up happening;

1500 calorie deficit graph

They’ll be super motivated and stick to their deficit for 2-3 weeks, but then life will get in the way, and they’ll exceed their calorie target, put on some weight, then give up entirely, stop dieting and end up heavier than they were in the first place.

Contrast that with a slower, more conservative approach using a 500-calorie deficit 

You can see above that that the initial results happen much more slowly.

By week 3, the person using a 500 calorie deficit has only lost 1kg, 2kg LESS than the person on the 1,500 calorie deficit, but crucially, the lower deficit is MUCH easier to stick to long-term, meaning it can be seen through successfully for 12 weeks.

When You SHOULD Have a Large Calorie Deficit 🥗

This isn’t to say that no one should eat a low-calorie diet, or have large calorie deficits.

Large deficits may work for;

  • People that are already very heavy (obese)
  • People that are consistently very active
  • Professional sportspeople trying to make weight for a one-off event

In fact, the NHS in the Uk do recommend very low-calorie diets (diets of 800 calories per day and under) to obese people but acknowledges that these sorts of diets are NOT suitable for most people since they come with many potentially negative side effects.

One of the most severe side effects is the loss of lean body mass. Dieters should be aiming to lose fat, rather than muscle tissue since muscle loss can create a whole host of it’s own issues.

What Does the Science Say? 🔬

I’ve worked with lots of clients on weight loss [rograms so I have a good general idea of what works and what does, fo different types of people, but let’s take a look at the scientific consensus.

This 2021 meta analysis states that “deficits of 500–750 calories per day have been used for weight loss and are recommended by many obesity societies and guidelines”.

In the scientific literature, this appears to be the baseline recommendation, while there is is evidence to show what the upper thresholds of a calorie deficit should be. This study points out that

greater severity of caloric restriction was related to lower dietary adherence, suggesting that moderate calorie restriction relative to energy needs would be preferable for dietary adherence “

This acknowledges that the most important aspect of a diet is the size of the deficit, but the ability to adhere to that deficit. Sure, a 1000 calorie deficit will produce quick weight loss, but if you can’t stick to it, it won’t produce ANY weight loss.

This study rightly points out that the diet and size of the ideal deficit is highly individualized, and that

developing guidelines may need to take several factors, such as population age and starting body weight, into consideration when formulating a suggested caloric deficit

And this is where weight loss coaching comes in. A coach will be able to help you determine the size of deficit you need to be in, and over what time period based on a number of different physiological and lifestyle factors. Your coach will also be able to help you plan fluctuations in the size of your deficit over time.

In fact, this study showed that after very low-calorie diets, a phase afterward ;

“including behavior therapy, nutritional education and exercise, improves weight maintenance”.

This proves that very low calories diets can work in some instances, but require outside intervention in order to ensure that weight regain doesn’t happen. Moral of the story? Hire a coach!

Can a Calorie Deficit Be Too Small? 🐢

So we know the issues with calorie deficits being too large, but what if they’re too small?!

The advantage of a small calorie deficit is that they’re easier because you’ll be dieting on MORE calories, which means making FEWER sacrifices (although it’ll still be a far cry from eating ad libitum).

Win-win, right, you get to lose weight and still eat some of the stuff you love.

Well, not so fast (literally)…

The main problem with small calorie deficits (100-300 calorie deficits) is that they produce very slow results.

For example, a 100-calorie deficit would only result in a loss of around 0.25lbs (0.1kg) per week, or 1lb (0.5kg) per month.

The chances are, if you’re going that slow you’re going to see so little change from week to week it’s going to be tough to maintain any form of motivation.

Having said that, this study notes that

even small reductions in energy intake (~100 kcal), coupled with increased physical activity, can help reduce weight gain (19) and may have a greater likelihood of being sustained in the long term

So a small deficit, coupled with a small increase in physical activity can add up to a moderate deficit which is easy to maintain long term

Also, losing weight that slowly just sucks.

In six months you’d only lose 3kg, and if you weigh 90kg+, you’ll barely notice that 

So, while dieting too quickly has its downsides, i.e. it’s damn tricky to maintain a large deficit long term, losing weight too slow also isn’t ideal

Summary 📝

So, as with most things in life, the answer doesn’t lie in either of the two extremes, but somewhere in the middle.

In my experience with myself, and having worked with dozens of clients over the years, I’ve generally found that most clients will lose weight at an average of 0.4kg per week, or 1.6kg per month.

This doesn’t sound cool or exciting, but it is what people naturally gravitate toward, and therefore probably a target that most people should aim for.

In order to lose 0.4kg per week, you’d need to be eating in a deficit of around 500 calories per day. For an average person that uses around 2,500 calories per day, that means eating around 2,000 calories per day.

That’s more than achievable and for most people, will produce results that happen fast enough to allow you to see visual changes week-on-week and keep you motivated, without being too restrictive, leaving you starving or disrupting your work/social/family life too much.

So, I recommend that most people stick to a calorie deficit of somewhere between 300-700 per day.

References 📕

Optimal Diet Strategies for Weight Loss and Weight Loss Maintenance:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8017325/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3447534/

https://link.springer.com/article/10.1007/s12325-020-01562-0

https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2001.134

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