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How to lose weight as quickly as possible

Posted on | Last updated 19-06-2017

When a person starts out to lose weight they usually have a target number of some kind in sight. Usually a number on the scales or a dress size, something like that. In most cases they want to achieve that goal as quickly as possible, often without making any changes to their lifestyle. Seriously, I have had numerous enquiries where people have said something along the lines of…

I want you to help me lose weight but I love my food so I’m not going to eat less.


I want to lose weight but I don’t want to do any exercise.

It’s in cases like this that you have to question the person’s commitment to change. I’ve written about this on numerous occasions. If you aren’t willing to change the habits that you have cultivated to this point, the very habits that have got you to the point of needing to lose weight because you have gotten fat, then you aren’t going to lose that fat. In order to become the version of you that you want to be you must change the version of you that currently exists. This means changing your thinking, your habits, your food choices, your exercise and activity levels and, ultimately, your priorities. The last one is important, because if you don’t view yourself as a priority in your own life then you won’t make the changes that are required and you won’t lose weight.

Keep that last point in mind because I will come back to that.

But, what about this fast weight loss? There are a few ways you can lose weight quickly. Cut off your legs, instant weight loss right there. Stop eating, starvation will lead to extreme weight loss (just look at Christian Bale in The Machinist). But seriously, to lose weight you MUST be in an energy deficit and to lose weight quickly you must be in a BIG deficit.

Is fast weight loss safe?

We all have what is known as a basal metabolic rate, this is all the energy needed for your body to operate at a very basic level, like if you were to lie in bed for 24-hours, like that Sloth dude in the film Se7en.

As a rough estimate, you can use a simple predictive equation to find this, your weight in pounds (KG x2.2) multiplied by 10 for a female and 11 for a male, or use a calorie calculator, you probably already have one on your mobile phone. This is a ball-park figure, not a precise calculation but it gives you decent idea. Work yours out now and have a look at that number, it’s likely to be higher than you thought. A lot of rapid weight loss diets recommend aiming for 1,200kcals per day. This is likely to be below BMR for most normal sized people and almost certainly too low for most overweight people.

To lose weight you only need to be in a deficit ranging from 5-20% I usually have clients aim for around 10% for sustainable fat loss. This is because slow and steady is much easier, the greater the energy deficit the less energy you will have, the less motivation you will have, the harder your workouts will be and the harder it is to maintain lean mass. A 1,200kcal diet is likely to result in much of the weight lost coming from lean tissue, like muscle and from water, due to glycogen (the fuel stored in your muscles and liver) depletion.

It goes without saying that if you are losing muscle then your BMR will go down too, because body fat doesn’t require as much energy as muscle. Your body loves homeostasis, it’s a survival mechanism and the less fuel you put in the tank the less willing your body will be to work. So a reduction in energy balance results in an automatic reduction in non-exercise activity (NEAT). This means that you move less and burn fewer calories, just ask anyone who has dieted down to extreme levels of leanness. They often have to dip close too, or even below their BMR, in order to keep losing fat. This is a stress inducer which can start to screw your head up. You might find not yourself talking to volleyballs, like Tom Hanks in Castaway, but you will almost certainly develop obsessive thinking about food and unwanted binges (1).

Is it rapid weight loss sustainable?

We are often told that low and steady is the way forward for long term change. However, it has been shown that fast weight loss in the first month of a diet can lead to better adherence and better long-term results (2). This is possibly due to the motivating factor of seeing a big chunk of the excess weight coming off so soon, combined with an improved sense of self-confidence, mobility and improved body image. In other words, you can see some light at the end of the tunnel.

However, other research has shown that there is no difference between either fast or slow weight loss in avoiding weight regain (3). There seems to be a little confusion about what is or isn’t effective and there are many myths and misunderstandings about what is or isn’t viable.

But what we do know is that creating an energy deficit is essential, this means going on a diet of some sort (4). We know that genetics don’t play as big a role as environment (4) and we know that timing is pretty irrelevant (1,4) so what’s missing?

The trouble with many diet interventions is that they don’t provide adequate education, a successful model for habit change and they don’t address the mindset element. If you don’t see yourself as a priority, if you don’t appreciate the value in investing in yourself you won’t have the motivation to make the lifestyle changes needed… I’m starting to repeat myself now.

Why attempt rapid weight loss?

Seeing as I have established that there may be some advantage to losing weight quickly, at least in the first month of a weight loss intervention it stands to reason that many people will want to know how to achieve this. Just be aware that the faster the loss the more difficult the process is going to be and if you’re more than a little overweight, the greater the chances of being left with unsightly loose skin. Skin is elastic and if it doesn’t have time to adapt to the loss in physical bulk it may not shrink. Either way you will almost certainly be left with some stretch marks.

However, the main reason that people choose to go on crash diets is that they have set themselves an, often unrealistic, short term goal. This might be that they have been ordered to lose a significant amount of weight by their doctor, perhaps prior to surgery. Or it could be a self-imposed goal for something far more superficial like a social event, usually weddings or holidays.

How many times do you hear people say that they need to get in beach body shape, or drop a dress size in a couple of weeks. I even had a cyclist come to me recently who wanted to lose 5 kilos of body fat in 3 weeks prior to a challenging cycling challenge in a mountainous region. It’s times like this that I am made to realise that people have their priorities all wrong and almost always leave it until the last minute. This doesn’t just go for weight loss either. I have had cyclists come to me for a bike fit the day before they are due to fly out for a week long training camp or the day before an Ironman race. Talk about last minute dot com!

Once again, this takes us back to my initial point about priorities. If you get your priorities right, if you are invested in a healthy lifestyle then you shouldn’t ever get to the point where you need to go on a crash diet to lose silly amounts of weight in a ridiculously short space of time.

But, seeing as this isn’t the case, or maybe you have just miscalculated - let’s go with that, I’ll be nice to you – You want to know how to lose weight quickly without having to cut your legs off don’t you?

How to lose weight quickly

First off, I want you to understand a few things. For a start, you won’t want to be doing this for much longer than about 2 weeks without a week or so eating a little more normally, and the fewer cycles of that you can do the better. Secondly, this is by no means a prescription and, as I have explicitly outlined above, I don’t consider this to the answer to your problems, nor do I consider it healthy, either physically or emotionally. Thirdly, only do this if you already have a good grasp of the composition of foods, have a healthy relationship with food and aren’t using this to paper over the cracks of a poor relationship with the person in the mirror. Forthly (is that even a word?) I don’t advocate starvation diets or liquid only diets and, in fact, would urge you not to do this at-all.

"Losing weight quickly can be done, but rarely safely".

It should go without saying that exercise isn’t a great idea while you are doing this. If you train with weights, have a de-load and maybe just do 2 light sessions. For everyone else stick to walking and gentle mobility, nothing too vigorous.

  1. Be prepared to feel like shit. You will be in a big energy deficit, your sleep may be affected, your mood definitely will be affected, you will have less energy and you’ll likely get a lot of cravings while your body struggles to deal with the low energy input.
  2. In an attempt to maintain as much lean mass as possible set protein at at-least 2 grams per kilogram of bodyweight. But, use your target weight rather than your current weight.
  3. Eat ALL the vegetables, lots and lots of low carbohydrate vegetables like leafy greens, alliums, peppers, crucifers, etc. You need as many micronutrients as you can get because you are eating way below your maintenance.
  4. Drink plenty of water, this will help to reduce the sensation of hunger but, if you are drinking a lot more than usual you may want to add some sugar free electrolytes to help energy release.
  5. Eat no starchy carbohydrates, barring the trace amounts in your vegetables.
  6. Fats are still important for your health but because you need to be in a big deficit I would keep them to around 0.3-0.5g per kilogram of your goal weight. Make sure that includes some fish oil.
  7. Maybe consider a 16-20 hour daily fast by skipping breakfast and then just having two main meals with plenty of protein and veggies.
  8. Don’t drop below BMR for longer than a few days at a time unless you really do have a lot of weight to lose.
  9. Take a good quality multi-vitamin and mineral supplement to reduce the chances of developing dangerous nutrient deficiencies this will do it.
  10. Don’t do it at all. Instead, get your priorities right. Focus on the values that are important to you in order to develop a healthy lifestyle where the ideas of exercising 4-5 times per week, preparing and eating healthy meals and practicing some kind of self-compassion are second nature to you rather than annoyances.
  11. Summary

So, just to sum it up, losing weight quickly can be done, but rarely safely and should always be a last resort. However, there may be some benefit to creating faster weight loss in the first few weeks of any diet intervention. Just do your best to avoid crash diets, fad diets and don’t so it if you don’t really know what you’re doing.

My advice, as you might already have gathered, is to get your shit together and sort your lifestyle out. Change isn’t easy but it can be a lot easier with support than doing it on your own. That’s why there are coaches like me in the world. 


  1. Collier R. Intermittent fasting: the science of going without. CMAJ : Canadian Medical Association Journal. 2013;185(9):E363-E364. doi:10.1503/cmaj.109-4451.
  2. Nackers LM, Ross KM, Perri MG. The Association Between Rate of Initial Weight Loss and Long-Term Success in Obesity Treatment: Does Slow and Steady Win the Race? International journal of behavioral medicine. 2010;17(3):161-167. doi:10.1007/s12529-010-9092-y.
  3. Katrina Purcell et al. The effect of rate of weight loss on long-term weight management: a randomised controlled trial. The Lancet Diabetes & Endocrinology, 2014.
  4. Casazza, K et al. ‘’Myths, Presumptions, and Facts about Obesity’’ NEJM, 2013

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