Are crash diets ever a good idea for weight loss?

Medically reviewed by Dr Louise Wiseman MBBS, BSc (Hons), DRCOG, MRCGP, words by Anna Bonet
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From Netdoctor

Crash dieting can be tempting in many ways, offering a quick and relatively easy 'fix' to your weight loss woes. Popular crash diets include the juice diet, the 7-day detox diet, the military diet and the infamous keto diet. But while they often promise rapid weight loss results, whether crash diets are sustainable or indeed damaging to your health in the long term is another question.

We speak to registered dietician, Helen Bond about the pros, cons and potential risks of crash dieting for weight loss:

What is a crash diet?

A crash diet is essentially any type of weight loss diet undertaken on a short-term basis with the aim of excluding some (or all!) major food groups in order to achieve rapid weight loss results.

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Why do people crash diet?

Diets where you lose weight very quickly can be tempting, particularly if you have an end goal or event in mind.

'A crash diet is typically a very low-calorie diet, where you eat a very restrictively for a short period of time,' says Bond.

'Crash diets are often hugely temping as they offer a quick-fix solution to a long-term problem – they often promise rapid weight loss, usually more than 2lbs of body fat a week, for little effort,' says Bond. 'However, such severe restrictions on food and calorie intake aren’t sustainable, so it’s not long before people revert back to the eating behaviours that made them put weight on in the first place.'

Crash diet health risks

What are the potential health risks of a crash diet? While crash diets can be simple to follow – they often only require you to reduce your calorie intake –so your health can seriously pay the price.

'Quite simply, crash diets are bad news,' says Bond. 'They are nutritionally unbalanced and can lead to long-term poor physical and mental health.'

'Low blood sugar levels can leave us feeling tired, irritable, lacking in concentration and unable to function properly,' Bond explains, 'while extreme hunger means we can end up overeating when we finally do eat - and often choose less healthy foods - and the pounds start to pile back on.'

Crash diet side-effects

Crash dieters also often get then get into a cycle of yo-yo dieting and adopting an ‘all or nothing’ approach to eating, often gaining more weight and losing confidence in the ability to lose weight in the long term.

According to Bond and the NHS, the main side-effects of a crash diet can include the following negative symptoms:

  • Weakened immune system
  • Dehydration
  • Dizziness
  • Irregular bowel movements
  • Fatigue
  • Irritability
  • Headaches
  • Hair thinning
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Crash diets: the verdict

The only diets that work are those that are sustainable in the long run, and a crash diet is not an example of this.

There is currently a large trial underway involving using a low calorie diet to reverse the diabetes of Type 2 diabetes sufferers. This is under careful monitoring of specialist doctors with careful management of blood sugars and patients' health. This is different to short term crash dieting with no clinician guiding you.

'By definition, "going on a diet" infers there’s a start and stop date, meaning you only change what you eat during these times,' says Bond. 'The result: when you finish your diet you return to the same unhealthy eating habits that put on pounds in the first place.'

'The foundation for losing weight – and keeping it off – is to eat a nutritious, well-balanced diet that’s packed with foods from each of the five main food groups, as shown in Public Health England’s Eatwell Guide, eat appropriately sized portions and be physically active.'

But how much exercise should you carry out? 'Aim for at least 150 minutes of moderately intense aerobic exercise a week and do strength training at least twice a week,' adds Bond.

If you're serious about your heath and fitness goals, think of healthy long term lifestyle choices, not short term restrictive diets as the key to achieving and maintaining a healthy weight.

Last updated: 14-02-2020

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