People wishing to lose weight often look into many diets, slimming programs and exercise regimes. The desire to drop pounds quickly often leads people to crash diet- that is, consume a very low number of calories in order to drop a lot of weight very quickly.

People who embark on a crash diet may do so for a short term goal, such as slimming down briefly for a wedding, or they may think of it as a way to kick start a long term weight loss program.

But does crash dieting work? We take a deeper look at how crash diets work and if they are a good way to lose weight.

How Do Crash Diets Work?

Crash diets work by using a huge reduction in calories to catalyze a loss in body mass. The average adult needs around 2000 calories per day to function healthily, and when a person consumes fewer than their needed amount, the body uses its own resources to make up for the required energy, leading to weight loss.

One pound of fat contains 3500 calories, so people on a diet that provides them with 500 fewer daily calories than they need will lose one pound per week.

When people crash diet they may consume up to 1000 calories less than they need, leading to a weight loss of two pounds per week.

This may be used in conjunction with exercise to burn even more calories, as well as stimulants such as caffeine to encourage increased metabolism.

There are many examples of crash diets, which may also be known as ‘very low calorie diets’ or VLCDs.

These include juice cleansing diets (where the user consumes nothing but juice), the grapefruit diet (where the user consumes grapefruit with every meal), the cabbage soup diet (where the user consumes only cabbage soup), the cayenne pepper diet (where the user consumes large quantities of warm water with cayenne pepper and maple syrup) and the Hollywood diet (a 48 hour diet where users consume a ‘special juice blend’ for fast weight loss.

A typical example of a daily food plan for a crash dieter:

  • Breakfast: one apple and two cups of fresh ginger tea with no sugar or milk
  • Lunch: a large salad consisting of mainly lettuce and cucumber with tomatoes, red peppers and half a can of tuna.
  • Dinner: a lean, grilled chicken breast with no sauce or dressing with steamed vegetables.

Do Crash Diets Work?

Technically, the answer is yes and no. Below we’ve broken it down into further detail:


Losing weight can be thought of as simple maths- in order to lose weight people simply need to eat less than they burn. Crash diets enable people to significantly reduce their calorie intake, leading to the rapid weight loss they are looking for.

They are better for people who are significantly overweight as the initial fast weight loss can provide a boost in motivation to keep up a healthier lifestyle.

Crash diets do not require any specialist nutritional knowledge, products or equipment which make them a good option for people who have not got a good understanding about food and nutrition. They also provide an opportunity to shift a few extra pounds in a quick and convenient way for special occasions such as a wedding or birthday celebration, without a drawn out process.

There are plenty of websites about different kinds of crash diets with easy to follow steps, recipes and advice. Crash diets can also be good for people who do not like exercise as they are a way of losing weight while keeping their usual routine – in fact strenuous exercise would be contraindicated for people on a crash diet due to low energy reserves.


Crash diets, including organized ‘very low calorie diets’ sold by dieting companies, are risky at best and dangerous at worst.

Embarking on a significant calorie deficit causes extreme hunger, leading to the risk of malnutrition as well as overeating when dieters binge due to hunger. A lack of energy in those on a crash diet can lead to lethargy and depression as well as an inability to exercise, which is both unhealthy and unhelpful to the metabolism.

A study by Oxford University found that crash dieting has a negative impact on heart health, causing a transient deterioration in heart function. It also found that despite an overall fat loss, the participants had an increase in fat within the heart of up to 44% throughout the diet, causing a temporary increased risk of heart attack [1].

Crash diets can also weaken your immune system, cause dehydration, palpitations and shortness of breath. Lack of essential nutrients can create skin problems and greasy hair as well as halitosis (bad breath) [2].

A sensible balanced diet combined with an appropriate exercise plan is a much better way to lose weight and keep it off long term.


Crash diets are a fairly popular but risky diet method that have no solid scientific support for long term health and wellness.

Dieters are very likely to regain weight after stopping the diet, as crash dieting does not help to educate users about sustainable healthy nutrition and long term weight loss and maintenance behaviors; it may also slow the metabolism. Several deaths have been reported from crash dieting and multiple diet companies have been shut down due to the dangers of their diet recommendations and products [3].

We would not recommend crash dieting to people looking to lose weight; rather an increased exercise program and moderate calorie deficit diet rich in vegetables is a better option. This is not intended as a substitute for medical advice; speak to your physician before changing your diet or embarking on a weight loss plan.

Hannah Canavan
Hannah Canavan
Researcher at DietProbe
Hannah is a health and lifestyle journalist with a passion for veganism and nutrition.
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