Why crash diets don't work

Crash diets refer to a variety of dietary approaches that all involve a severe reduction in your calorie intake over a short period of time, for example, the very low calorie diet (VLCD). Many people try crash dieting to achieve rapid weight loss, although crash diets have been associated with sporting performance and bodybuilding. 

Do crash diets ever work?

Whether or not a crash diet works depends on what your goals are, and whatever they are, it’s always recommended to carefully assess the risks and benefits with a specialist medical professional, such as a dietitian. 

In some cases, crash diets are dangerous and should not be tried. Children and pregnant women should not try crash diets. You should also avoid crash dieting if you have certain health conditions, including heart disease, kidney disease, certain types and stages of liver disease, type 1 diabetes or gout. 

If you’re an athlete, forms of ‘crash dieting’ have been used to improve performance or outcomes but it can also negatively affect your long-term health. Speaking to a dietitian can, therefore, help you make an informed decision about this approach. 

If you’re trying to lose weight quickly before a medical intervention, your care team can provide you with advice on how to safely do this and whether it is appropriate. This may involve seeing a dietitian for tailored advice. 

If you’re living with a heavy weight, with a BMI of over 35, and are looking for a way to achieve long-term weight loss and weight management, crash dieting is ineffective. Research shows that in the long term, crash dieting increases weight. This is because obesity is a complex condition, with multiple factors that affect it.

Why crash dieting doesn’t work for weight management

Restricting your calorie intake and exercising more is not enough to guarantee long-term weight loss if you are living with a heavy weight, particularly if your BMI is over 35. This is because behaviour is only one of multiple causes of obesity. One major factor is your set point weight. 

Your set point weight refers to a predetermined weight range that your body aims to maintain. This is determined by many factors, which include your biology and genetics and is, therefore, unaffected by your behaviour. 

As a result, when crash dieting, your body fights back to maintain its set point weight by making changes, for example, to your metabolism or your hunger signals. 

How to achieve sustainable weight loss

It isn’t easy to achieve sustainable weight loss if you are living with a heavier weight but it is possible with a tailored approach. Every individual body is different, so what works for one of your friends may not work for you. 

A good place to start is to see your GP, who can refer you to the appropriate specialists and/or a multidisciplinary team. You may see a dietitian who will assess your weight challenges, including how you’ve approached weight loss in the past, as well as ask you questions about your lifestyle, family history, as well as mental and physical health. 

A clinical team can then construct a tailored treatment plan that may include changes to your nutrition and lifestyle, as well as medical, psychological and surgical interventions. 

When to seek help for weight management

While BMI is used as an indicator of whether your weight is within a ‘healthy range’ or if you’re living with a heavier weight, it’s not an effective measure of whether it would be helpful for you to lose weight on its own. It’s, therefore, important to have a medical assessment when you feel you need it — this may be before your BMI reaches 30 or higher.