Are Crash Diets a Good Idea?

You’ve likely heard the term “crash diet” before. A quick search of the internet reveals a ton of different articles - some of which are more helpful than others[1-3].

A majority also touch upon the reason behind crash dieting - “Lose weight fast with no strings attached! It’s as easy as x!” The problem is, there are strings attached and it’s not that simple either.

When it comes to weight loss, slow and steady is often the best method. However, this is neither as exciting nor as easy. It may seem easier and even more exciting to make a drastic change, especially when it’s only for a set period - but this is temporary[2,4].

With the slow and steady route, we’re talking about changing habits for the long run through small changes to your intake and lifestyle. At the start, it can be a bit harder to do this and it takes patience, but it can lead to weight loss you maintain as well as a healthier relationship with food and your mind/body too.

What is a crash diet anyway?

There is actually a definition for crash diet in the dictionary. Unfortunately, if nothing else, this shows you how popular the term has become. The definition for crash diet is “a way of losing weight very quickly by limiting how much one eats”[5]. Overall, most crash diets restrict energy intake as well as specific nutrients - or they may only allow certain foods to be consumed to promote rapid weight loss[1-3].

In current research on this topic, there is a struggle to define what “rapid” weight loss means because specific parameters can vary from one study to the next[6]. However, general guidelines for safe and gradual weight loss exist and they recommend not to lose more than 2 pounds per week[7]. Anything more than this could therefore be considered rapid.

We also have a page on site that reviews fat loss (see here), including recommended calorie reductions for healthy weight loss. Generally, calories per day can be a useful starting point, but it shouldn’t be the only consideration or the main focus. Focus first and foremost on how you are feeling rather than the number of calories consumed. From there, proceed to tinker until you figure out what works best for you.

Excess body weight (fat mass) as well as medical history are also important factors to consider[4]. For example, some may lose weight in less time than others, while others may have a bit of a harder time losing weight due to certain medical conditions.

Are crash diets bad?

Through crash dieting, an unhealthy and unhelpful cycle can be created. This is the cycle where you are constantly working to lose weight fast followed by gaining it back and then falling back into losing weight again. Unfortunately, this is what crash dieting usually leads to and it can be harmful both physically and psychologically[1,2].

What does the research say?

Current research is inconclusive on rapid weight loss and its effectiveness because there are so many variables at play. These variables include medical history, age range, dietary choices, and physical activity level of the participants.

With that being said, there are themes in the research which are important to note[4,5,8]:

  1. Rapid weight loss has been shown to decrease your daily energy needs more than gradual weight loss. When energy needs decrease, this means you require fewer calories each day to maintain your weight. At the end of the day, a larger decrease in daily energy needs can make it harder for you to maintain your weight loss over time.
  2. Gradual weight loss has been shown to promote a greater decrease in fat mass when compared to rapid weight loss. A decrease in fat mass is what you should aim for if you are looking to lose weight, rather than a decrease or change in muscle mass.
  3. It can be challenging to compare weight loss research due to differences in dietary intake from one study to the next. However, there is usually an emphasis on the importance of adequate protein intake for muscle preservation.

Lastly, a staggering statistic is that just 15% of individuals who rapidly lose weight manage to maintain this weight loss over a longer period[8]. This further suggests the importance of making habitual changes and not just fast and easy ones that you don’t expect to maintain.

What Should You Do Then?

If you’re looking to lose weight quickly, first ask yourself why you are looking to lose weight. Is it for health or for something else, like “looking good for x event”?

If the reason is for health, then you should start by making small changes to your dietary intake and lifestyle. Any change you make can be beneficial and while it may feel like you need to make these changes right away, in the long run, your health will thank you for taking it slow. These changes can be something as simple as increasing your fruit or vegetable intake or decreasing your sugary drink intake for just one day during the week and then progress to two or three days when you feel ready. Make the changes manageable.

If you are looking to include Huel to better your health, start with once per day where you have it one or two days during the week. Try to resist the idea of swapping over to 100% Huel to “lose weight in x amount of time.” We don’t recommend this and it is not sustainable. Huel is not a crash diet, it’s food.

Lastly, if the reason you are looking to lose weight fast is to “look good at x event,” then the first thing to do here is to stop and try to think about why. Zoom in on your relationship with food and your body. What is stopping you from feeling “good” now? This question may sound simple but it can be one of the most challenging questions to address as it has to do with many factors.

It can also be challenging to know what exactly is the best route to take and how to navigate all of this. With nutrition, there is a tendency to want to do things quickly and make all the changes right now. Ultimately, no matter the scenario, we have to be patient with, and easy on, ourselves. One thing you can do right away is to reach out to a medical professional or a friend/family member for support along your journey. Take it day by day.

Next up - make small changes that make you happy. Whether that’s getting outside before/after work or during your lunch break, having food that makes you smile, joining a club with individuals who share a similar passion, calling up an old friend, playing with a dog, or listening to some music. Do the things that make you feel good!

After that, start to work slowly toward your nutrition/health goals one day and one change at a time.

Recommended Reading


  1. Harvey-Jenner C. 9 Things that Can Happen to Your Body When You Crash Diet. Cosmopolitan. 2018. Date Accessed: 25 Aug 2021. [Available from:].
  2. Wiseman L. Are Crash Diets Ever a Good Idea for Weight Loss? NetDoctor. 2020. Date Accessed: 25 Aug 2021. [Available from:].
  3. Raj MA. Best Crash Diet For Fast Weight Loss, Diet Plan, Side Effects. Style Craze. 2021. Date Accessed: 25 Aug 2021. [Available from:].
  4. Stiegler P and Cunliffe A. The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports Medicine. 2012; 36(3): 239-262. [Available from:].
  5. Stiegler P and Cunliffe A. The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports Medicine. 2012; 36(3): 239-262. [Available from:].
  6. Ashtray-Larky D et al. Effects of gradual weight loss v. rapid weight loss on body composition and RMR: a systematic review and meta-analysis. British Journal of Nutrition. 2020; 124(11):1121-1132 [Available from:].
  7. Position of the Academy of Nutrition and Dietetics: Interventions for the Treatment of Overweight and Obesity in Adults. Journal of the Academy of Nutrition and Dietetics. 2016; 116(1): 129-147. [Available from:].
  8. Coutinho SR, et al. The impact of rate of weight loss on body composition and compensatory mechanisms during weight reduction: a randomized control trial. Clinical Nutrition. 2018; 37(4): 1154-1162. [Available from:].

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