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Why crash dieting could harm your health

23 Nov 2022 • 1 min read

Want to know exactly what happens to your body when you embark on a crash diet? Crash diets, detox programmes, and cleanses might seem appealing, with their promises of fast weight loss. But extreme and rapid diets are no good for your body or your mind. Here’s why you risk more than a big weight rebound if you do a crash diet.

What is a crash diet? 

There’s no official definition of a crash diet. Beware of any diet plan that restricts your calories to anywhere near your BMR, bans entire food groups, or promises huge weekly weight loss. Crash diets can make you feel unwell and put your long term health at risk. There are two main reasons for this. First, crash diets suddenly restrict your calories. Some even suggest you eat below your BMR - the amount of calories your body needs to survive on a cellular level. This extreme calorie restriction has obvious health risks, from exhaustion to muscle loss and potential disordered eating behaviour. Secondly, crash diets usually ask you to avoid entire food groups, macronutrients, or ingredients. This can leave you malnourished and lacking in nutrition including key minerals, vitamins, and essential fats. Your relationship with food might suffer on a crash diet, too. Because extreme diets don’t teach you how to lose weight sustainably, you won’t learn how to nourish your body on a daily basis. You might come to rely on pills, fat burners, cleanses or detoxes. When you finish the diet, you won’t know how to eat on a day-to-day basis. Some people who have crash dieted have lingering fears about carbohydrates, fats, gluten, dairy, fruit, or any treat foods.

How do crash diets impact your body?

You will lose weight on a crash diet. But the weight won’t all come from unwanted body fat. You will lose a lot of water weight (especially in the first week) and some muscle mass, too. We all lose lean muscle as we age. So rather than losing even more from crash dieting, we should be doing everything we can to keep muscle mass in adulthood. In extreme cases, this muscle loss can affect your heart muscle. Crash dieting can damage your heart and blood vessels, putting you at greater risk of heart disease and heart attack. Other long-term health risks linked to crash dieting include osteoporosis from calcium deficiencies, liver problems, and kidney failure. Crash diets can also slow your normal metabolic rate, making it harder for you to keep the weight off. If your metabolism is affected, you will find it difficult to diet in the future. You are actually slowing down your body’s inbuilt ability to lose weight. You might miss out on important vitamins, minerals, essential fats and fibre if you crash diet. This is especially true if the diet tells you not to eat certain foods, or asks you to replace food with shakes or smoothies. Because most crash diets limit your calories and reduce your carbohydrate intake, you will probably feel lethargic, exhausted, and could even find it hard to concentrate on work or studies. 

Will you regain weight after a crash diet?

Most people regain all the weight they lost on a crash diet, and some actually put on more. This means they end up in a worse place than when they started. They might have damaged their health, emotional wellbeing, or relationship with food in the process. After feeling so restricted on your diet, you find it difficult to transition back to normal eating. Your metabolism may have been down-regulated by the extreme low calories, so your body isn’t as efficient at managing your weight any more.   
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