Is it bad to lose weight fast

Is it bad to lose weight fast?

You’ve probably read articles and seen posts by people that say, it’s bad to lose weight fast. This is said for numerous reasons such as:

  • Being unsustainable
  • Wrecking your metabolism
  • It’ll make you malnourished
  • You’ll lose muscle
  • You’ll be miserable
  • You’re likely to binge
  • You’ll gain it all back

As with most things in nutrition, there is some truth to these claims. However, when looking at the evidence, most of these claims arent 100% true.

A lot of nutritionists and personal trainers will say you should never lose weight fast. But that is a too simplistic viewpoint on things. People are very different and for some people losing weight fast, might be exactly what kick starts their journey.

So in short “is it bad to lose weight fast?” No, not necessarily. In some cases it may be better to lose weight fast.

In this article, I’ll explain how you can lose weight fast. Why losing weight fast can be better for some people. Finally how to lose weight fast, so none of the points listed above will affect you.

This post isn’t saying you should only lose weight fast. It’s explaining why fast weight loss, isn’t the devil, it’s portrayed to be.

Why fast weight loss is shunned

The reason fast weight loss is shunned is that those that promote fast weight loss, usually do so from an unethical viewpoint.

When it comes to fast weight loss, it’s usually promoted through such shady measures such as:

  • Juice only diets
  • Weight loss teas
  • Detox pills
  • Extreme fasting diets
  • 800/1200 calorie diets (without context or flexibility)

When it comes to fast weight loss, these are the methods people tend to use. So I imagine, this is why people get worried about the idea of losing weight fast. Let’s be honest juices, pills and tea’s are not a good way to spend your money.

It is true, people follow these diets, they tend to gain most their weight back. The problem with these diets is that don’t educate and empower the users to sustain lifestyle habits to keep the weight off for good. People will religiously follow these protocols for a month, lose a load of weight, go back to their old patterns and regain the weight.

Therefore well-meaning nutritionists and personal trainers will say follow a slow and sustainable plan. The idea being, you can educate yourself about nutrition, do something you don’t hate and make long term sustainable changes. Don’t get me wrong, I’m not saying that’s the wrong thing to do. For a lot of people, that’s probably what they need.

What I’m saying is, just because some bad companies have abused the idea of fast weight loss, it doesn’t mean people should never lose weight fast and it doesn’t mean it is bad to lose weight fast.

Standard recommendations

There are 2 usual ways weight loss recommendations are made.

There are either the standard 500 calories a day deficit. Which I am really not a fan of. Or there’s the percentage calorie deficit, which I am a big fan of.

500 calories a day deficit

The reason I’m not a fan of this method is that it’s too simplistic.

In general 3500 calories makes a pound of fat. So 500 calories, 7 days of the week makes one pound at 3500 calories.

The thing is, people, come in a great variety of shapes and sizes.

An obese man at 300 pounds, who would be at a healthier weight of 180 pounds for example. It would take him years to get there on a 500 calorie deficit.

Percentage deficit

This is where you take somebody’s calorie maintenance and make a deficit based on the percentage of that maintenance. So for example someone on a 2000 calorie maintenance at 10% would have a 200 calorie deficit. Therefore they consume 1800 calories per day.

This is the percentage ranges I currently go by:

  • Small deficit: 10-15%
  • Moderate deficit: 20-25%
  • Large deficit: 25% +

I prefer this method, because no matter the shape or size of the person, the calorie deficit and weight loss, will be in scale to their size.

As this post is talking about whether it’s bad to lose weight fast, I’ll be talking about large deficits of over 25%.


Without doubt, if you’re consuming far fewer calories, you will be consuming less vitamins and minerals, than you would if you ate at maintenance calories.

However, this is anecdotal and I could be wrong. But most people I’ve worked with and myself included. Our nutrition quality tends to improve when dieting. This is because if you’re eating fewer calories, you need to eat more foods that fill you up. This means focusing your diet on foods that are low in energy density. This means eating more fruits and green vegetables. Eating more lean meats and beans. These foods are lower in calories and are very filling.

The standard western diet tends to be very low in nutrients. It’s mostly high sugar, high fat, high salt foods. (1)

These foods tend to be very calorie-dense, with little nutrients. Therefore consuming more nutrient-dense foods despite having fewer calories tends to give people more nutrients.

But to the point. Yes, a very low-calorie diet will potentially be less nutrient-dense compared to a diet with a smaller deficit.

The thing is, a very low calorie diet, isn’t going to last long. So you can go back to maintenance sooner.

To potentially offset this, I definitely recommend standard fish oil, especially if your diet does not include oily fish. It might also be a good idea to take a multivitamin just to cover your bases. This is the only time I’d suggest taking one. You should be able to get most of your nutrition from food, especially if you’re eating lots of fruit and veg. But it wouldn’t hurt to cover your bases.


We’re told to diet slowly because supposedly losing weight fast is unsustainable. Which makes sense. If you had to do a juice cleanse or something, of course, it will be unsustainable. You won’t be getting adequate nutrients and your life will most likely suck.

But what if I was to tell you something, that may be blow your mind?

Dieting is not supposed to be sustainable. If you dieted forever, you’d die.

When I say dieting, I mean eating at a caloric deficit. This is basically starving yourself. When your body doesn’t get enough energy from food, it breaks itself down to provide energy. If you sustainably did that forever, you’d eventually die of starvation. So dieting sustainably isn’t something you’d want to do anyway.

The whole point of dieting is to lose a certain amount of body fat. Once that is done, you can then eat at maintenance calories, to stay at the same weight.

Now eating at maintenance calories is supposed to be sustainable. Therefore if you lost weight faster, you’d be able to eat at maintenance sooner, compared to dieting slowly. Dieting slow or fast sucks regardless, therefore for some people, it may make more sense to get it over with faster.


There’s a thought that if you diet too fast, you’ll wreck your metabolism. It’s said if you eat too little, your body will stop you from losing weight. It goes into starvation mode, thus your body starts holding onto fat to survive.

Well, I wrote a piece about this. This idea of your metabolism crashing because of your diet, isn’t quite true.

It’s not starvation mode where your body holds onto fat, due to starvation. But it’s called metabolic adaptation. Metabolic adaptation is real, but a little different.

When you lose weight you burn fewer calories. The less you weigh, the less you burn. This is not to be feared, this is normal and to be expected.

Your rate of NEAT also decreases. This is all your spontaneous movement. Walking, fidgeting etc. When your body takes in fewer calories, this is to be expected. This is your body trying to get you to burn fewer calories. Your body doesn’t know you have abundant access to food. This isn’t your body holding fat, but your body trying to get you to burn fewer calories.

Finally, your hunger hormones will increase. And your fullness hormones will decrease. This again is to try and get you to eat more calories, so you’re no longer in a deficit. This is to stop you from starving. But not your body holding on to fat.

Whether your diet is fast or slow, these changes will all happen. This isn’t your metabolism crashing, these are just normal bodily behaviours.

As for you losing weight and your calorie maintenance decreasing, there’s not much you can do. All you can do is just gradually decrease your calories more. The less you weigh, the fewer calories your body needs. More about that here.

As for your rate of NEAT decreasing. My recommendation is to get a fitness tracker and track your steps. So, if your step count decreases during your diet, by wearing a watch, you can make sure you’re still moving about the same.

Finally as for your hormones. You cant manipulate your hormones or anything like that. Anyone that says you can is lying. But if hunger is becoming an issue, the best thing you can do is have a diet break. Once you feel good again, then get dieting again.

Muscle loss

Muscle loss is another reason its been purported to not diet fast. People claim if you diet too fast, your body won’t only lose fat, but you’ll also lose muscle too. And indeed studies also show this is usually the case.

But when you look deep into the studies. The studies where people lose muscle from fast weight loss, the studies miss 2 fundamentals which may have made a big difference.

  • Lack of protein
  • No resistance training

One study showed that when 17 obese women were put on a 500 calorie per day some interesting things happened. They were split into 2 groups.

The groups were split based on protein intake:

  • 0.8g protein per kg of bodyweight
  • 1.6g protein per kg of bodyweight

The 0.8g group lost muscle, whereas the 1.6g group had no difference in muscle mass. Even on a 500 calorie a day diet. (2)

In 1999, a study was done on 20 people, comparing those on a super low calorie diet. They were split into 2 groups.

  • Resistance training group
  • Non resistance training group

In this study, both groups of people consumed 800 calories per day for 12 weeks. The non-resistance group only did cardio exercise, whilst the resistance group trained 3x per week, progressively adding weight.

On average the no resistance group lost 4kg of lean body mass, which equates to around 9lbs. The resistance training group didn’t lose any lean body mass. Also what I found more interesting was the resistance group also increased their BMR, this means they would burn slightly more calories at rest. (3)

I could cite plenty of other studies. But what they all show is, when adequate protein is consumed and resistance training is involved. You’ll preserve either all your lean body mass or you will preserve most of it. The thing is, even if you lost a little. Because you’ve lost weight so fast, you’ll soon be back to maintenance calories and whatever you’ve lost you’ll soon regain fast due to muscle memory.

How much resistance training do I need and how much protein should I eat?

From what the evidence suggests aim for double the recommended daily protein intake of 0.8g per kg.

Therefore aim for at least 1.6g of protein per target bodyweight per day. Some studies show 1.2g is enough. If you have a lot of weight to lose, you probably don’t need to be too fixated on the perfect protein amount.

When the body has so much excess fat, that will be burnt first. Muscle loss is more of a big issue when you are already slightly lean.

As for training, you really don’t need to do much. Hit each muscle at least twice a week and you’ll be fine. (4)

You’ll be miserable

It’s often said, that dieting hard and fast will make you miserable. However, there is some evidence to suggest this isn’t always the case.

In 2011, a study was done on patients with Type 2 diabetes. The participants were assigned a 450 calorie per day diet, to follow for 16 weeks. The participants all lost a lot of weight, 50-60 pounds. But what was noted, was that they all recorded that their quality of life improved during the diet.

There were several reasons as to why it’s believed their quality of life may have improved during the study. (x)

  • No longer having to rely on all previous medication
  • Fast weight loss is very motivating
  • Not having to be as fearful about their health
  • Better physical condition (Being able to move more easily)

There’s a saying about dieting. No matter how you do it, it kinda sucks. You just need to pick what sort of suck you’re willing to deal with. If your diet is slow, it may suck a little less as you can eat a little more, but you have to diet longer. Or you can just suck it up and get it over with asap. (5)

A systematic review of 17 very-low-calorie diets, concluded participants, in general, found it bearable. When looking at the number of people who dropped out of the studies it did range from 4.7% to 33%. But most of the dropouts were from the follow-ups to the studies, not actually during the study.

However it is important to note that the follow up periods did differ between studies. Overall, drop out rates ranged from 4.7% to 33% and appeared to be lower during the active intervention phase compared with during the follow-up period.

Sellahewa et al, 2017

If I was to make a few theories as to why some people do get miserable trying to lose weight fast, because they do, these are what I would say they are. These are just my thoughts, so hey I could be wrong:

  • All or nothing mentality – just because you choose to go low calorie, doesn’t mean you must do it every day.
  • Lack of plan – There will be times when you are more hungry, that’s why planning ahead is super important, so you don’t go binge.
  • You’re following one of the awful diets I listed earlier
  • You’re already somewhat lean – When already lean, aggressive dieting is harder, it’s better for people with a lot of fat to lose.
  • Not having implemented breaks.

Binge likelyhood

I can’t deny this is somewhat true. The number of people I see follow a 1200 calorie diet Monday – Thursday, then binge on Friday and the weekend and give up.

This is why a lot of health professionals recommend doing a slower and more “sustainable” diet. And for a lot of people that is great advice, no doubt about it.

In fact for people that always spend their lives on diets, I’d personally advise they spent a good chunk of time not dieting at all. Yes really. Though it may seem counterintuitive, it’s better to either pause or take a few steps back before going forwards.

This is a good opportunity for some people to know what “normal” eating looks like. Not many people experience proper eating at maintenance. What people learn about eating at maintenance calories is, you can eat a lot of food. By focusing the bulk of your diet on low energy-dense foods, with a little sprinkle of ‘junk’. You’ll realise you can eat a lot of food with plenty of variety, sustain your weight and feel great.

Once you have a good baseline of what normal healthy eating looks like. Most people are in a very good and healthy place to lose some fat and diet.

You’d assume if someone is dieting on lower calories, that they’d be more hungry?

Interestingly, the evidence doesn’t always say so.

A study in 2006, compared hunger levels between those on very low calorie diet with those on a standard low calorie diet for 11 weeks.

What was noted was that the very low-calorie groups hunger was significantly lower than the standard low-calorie group. This was noted after 5 weeks and after 11 weeks.

Participants in the VLCD demonstrated a greater decrease in cravings on all measures, with the decrease apparent after 5 weeks of dieting and continuing even after the first 5 weeks of a gradual transition to a food-based LCD

Martin et al, 2006

Though this is just an anecdote. I myself have noticed less hunger when on an aggressive calorie deficit compared to a moderate one. Same with clients. I’ve even had some say they think they could eat less, to get things done quicker. (x)

As for why this is the case, nobody is 100% sure. But we can throw out some theories. These are the theories from those that conducted this study.

  1. Fewer calories mean less variety. The richer the variety of food available the higher our drive to eat.
  2. There’s a theory that when people eat due to cravings that drives hunger more. But if you don’t eat, then cravings don’t increase.
  3. Due to the diet being lower in calories, it’s likely to not taste as good. Less palatable food is less likely to drive hunger. You’re more likely to eat chocolate if offered, but not broccoli.
  4. The fourth theory is, just by consuming less food, your body desires less food.

Regain weight

Another reason people claims it is bad to lose weight fast, is because you’re more likely to gain all the weight back.

In 2016, there was a study involving 57 overweight and obese participants. They were split into 2 groups.

  • Low-calorie diet for 12 weeks
  • Very low-calorie diet for 5 weeks

The low-calorie group on average lost 8.2kg and the very low-calorie group lost 9kg. Both groups afterwards were at maintenance calories for 4 weeks after the trial. Then 9 months after, their weights were recorded to see how much weight was regained.

The low-calorie group regained 4.2kg after the trial. The very low-calorie group regained 4.5kg. These differences are not significant.

This study showed that the speed at which you lose weight does not dictate how fast you gain it back. (7)

This study showed that, with similar total weight loss, the rate of weight loss did not affect long-term weight regain in individuals with overweight and obesity.

Vink et al, 2016

When reading this study I was wondering if both groups would have maintained more of the weight loss, if they were taught how to maintain properly. This is what was said in thei disussion:

In our opinion, the absence of dietary advice in the follow-up period reflects common practice, because most individuals with obesity do not receive dietary counseling after a weight loss attempt

Vink et al, 2016

Another paper stated this:

Collectively, findings indicate both short- and long-term advantages to fast initial weight loss. Fast weight losers obtained greater weight reduction and long-term maintenance, and were not more susceptible to weight regain than gradual weight losers.

Nackers et al, 2010

There is evidence from randomised intervention trials to support that a greater initial weight loss induced without changes in lifestyle e.g. liquid formula diets or anorectic drugs) improves long-term weight maintenance, providing it is followed by a 1–2 years integrated weight maintenance programme consisting of lifestyle interventions involving dietary change, nutritional education, behaviour therapy and increased physical activity. 

Rossner, 2001

As the paper above just stated. Instead of criticising the type of diet, maybe we need to put more emphasis on aftercare. Once someone has lost the weight, maybe it’s more important they are taught how to live afterwards, so they have full autonomy. It’s not losing weight which is the issue, it’s keeping it off afterwards.

Why I personally prefer fast weight loss

Whilst I do my best to cite evidence when writing, some of these points come from my experience and my experience with my clients. So, just because they work for me, doesn’t mean these will work for everyone else.


I have noticed, those who say you must only lose weight slowly tend to be people who have never struggled with their weight. When you are carrying a lot of excess fat, you want to get rid of it as soon as possible.

Yes, I do preach patience a lot and you will need it. But if you’ve never struggled with your weight, you don’t have the experience of wanting to get rid of it asap. So it’s easy to say let’s be slow and sustainable, but if there’s an option to go faster, of course, people will take it.

This is where motivation comes into play. When losing weight fast. You’re more likely to see large drops on the scale. Yes, I know it’s not fat loss. But seeing the large drop is feedback and tells someone they are on the right track. That positive feedback keeps you determined to soldier on. Therefore you’re more likely to keep up those habits that keep you going. This momentum snowballs.

More room for error

The thing with having a small calorie deficit is, that it doesn’t leave you much room for error. For example, let’s say you were put on a deficit of 300 calories per day. You will need to be able to measure everything you eat perfectly to the very gram, for it to be effective.

Realistically most people are going to be somewhat inaccurate. Also when tracking foods, what you track in your phone isn’t 100% accurate. Food labels are allowed to have a margin of error of up to 20%. (8)

So even if you do track accurately, you may still not be in a deficit, due to the potential error.

With a large deficit of lets say up to 1000 calories per day. Even if your measurements are inaccurate, you have such a large buffer, if you measure and track well, you are pretty much guaranteed to be in a deficit.


It’s faster. When you have over 50 pounds of fat to lose. You want it gone as soon as possible. If you’re ready and in the right frame of mind, there’s no reason to lose it in half the amount of time if you can.

Final thoughts

Do I think it is bad to lose weight fast? No.

Does that mean I think everyone should try and lose weight fast? No.

Am I willing to admit I have slight bias towards fast weight loss? Yes.

This post isn’t to say everyone must lose weight as fast as possible. Definitely not. Everyone is different and will react to things differently. This post was more of a rebuttal to the idea that it’s bad to lose weight fats and nobody should ever do it.

There are my take home points:

  • You can do a fast or aggressive diet with nutritious foods. It doesn’t need to be a juice cleanse or something like that.
  • As for nutrition, most tend to have poor diets before dieting, so actually eat more nutrients when they eat in a deficit, when focusing on more nutritious foods. But even though nutrition won’t be as good as maintenance, but fast weight loss is fast, so you can be eating better sooner.
  • Diets are not supposed to be sustainable, they’re a short stopgap, to shed some body fat. If you dieted forever you would die from starvation. What needs to be sustainable is the maintenance phase after you lose weight, so you don’t gain it back.
  • Your metabolism won’t crash. You may move less, thus burning fewer calories. If hunger does get too much, have a little break and eat at maintenance calories again.
  • As for muscle loss, the evidence is clear. Eat enough protein and lift some weights and it won’t happen. If it does, lost muscle is far easier to regain than building new muscle. So when you go back to maintenance, you’ll be fine.
  • Whether your diet slow or fast, life won’t be as fun as not dieting. Dieting faster means you get it over with sooner. It is your choice.
  • As for hunger, there is a lot of evidence and anecdotes showing people are actually less hungry on a super low-calorie diet.

Finally, as for weight regain, it’s not the diet that causes weight to regain. It’s what happens when people finish the diet. But if your diet was awful and super restrictive, of course, there’s a chance you will spiral into bad habits. That’s why it’s important to eat nutritious high volume foods and implement breaks to prevent this from happening.

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