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Home / Weight Loss / Losing weight fast: the dangers of crash diets

Losing weight fast: the dangers of crash diets

Millions of people around the world want - and need - to lose weight. The result of poor diet and inactive lifestyles, the West, in particular, is suffering from an obesity epidemic. However, it is important that we drop the pounds the right way and for the right reasons. Often when preoccupied with fast weight loss results, many dieters neglect their health.

To achieve and sustain a healthy weight, it is important to take care of your body whilst following a strict diet and exercise regime. Read on to learn about the health problems crash dieting can create.

broken plate and knife and fork

What is a crash diet?

A crash diet is a specific type of diet designed for rapid weight loss. Going by the terms “semistarvation diet” and “very low calorie diet (VLCD)”, a crash diet is controversial due to the health complications it can cause.

There are instances where a VLCD may be recommended, usually for morbidly obese individuals suffering from serious weight-related conditions. However, a doctor’s supervision should always be sought, and generally, a VLCD will be conducted in a clinical setting.

Losing weight at a rate of more than 1kg per week can pose many immediate problems and long-term health consequences. It is recommended that you lose weight gradually and with the guidance of a medical professional (especially, if you have other health concerns).

Often when people try to lose weight on a crash diet, it signals the beginning of a vicious cycle, where their weight fluctuates up and down, also known as “yo-yoing”. A yo-yo diet is when a crash diet is followed by binge eating and weight gain. In many cases, people put on more weight than they lost during a crash diet.

Examples of crash diets include:

  • cabbage diet
  • Atkins diet (low-carb diet)
  • juice cleanse/detox
  • paleo
  • beer diet
natural-food-healthy-eating-protein-diet The Atkins diet involves eating almost exclusively protein, with limited carbohydrates and fibre. sliced-boiled-eggsdecorated-parsley-leaves The cabbage soup diet does not restrict how much food you eat but seriously restricts your variety. eating-tasty-honey The maple syrup diet is where you only consume maple syrup with lemon, water and cayenne pepper.

And pretty much anything else that restricts major food groups.

Loss of muscle mass

The body is designed to stop itself from losing too much weight too rapidly. If you try to lose more than the advised amount of one to two pounds per week, you risk your body using up its muscle stores rather than fat stores for energy.

Aesthetically speaking, this reduction in lean muscle mass actually detracts from the effort of trying to lose weight, as muscle is what gives your body a toned physique.

From a performance perspective, a higher percentage of muscle mass also increases your physical performance when you exercise, which allows you to burn more calories. Having a higher muscle mass also speeds up the metabolism.

To prevent your body from using its stores of muscle mass for energy, you should always consume enough to properly function while you are trying to lose weight. You should consult a doctor or dietitian to learn how much that is you.

Metabolism changes

To maintain your weight, you should consume only as many calories as needed for the levels of physical activity carried out in a day. If the two match up, no weight will be gained.

fat burn diagram

When you don't feed your body enough calories, it may go into “starvation mode”, which is where your metabolism is slowed to avoid using up valuable energy. The body will hold onto any calories consumed because it doesn't know when more calories will be available, slowing the weight loss process.

If you make a habit of crash dieting, it can cause adverse long-term effects on the natural functioning of your metabolism, making it harder to control your weight in the future. It is far better to change your diet and lifestyle incrementally over an extended period, than to vastly reduce calories consumed to hit a target weight.

Nutritional deficiencies

One of the biggest challenges when reducing your overall caloric intake is to ensure you’re still consuming the right vitamins and minerals. Nutrients are essential to the body’s proper functioning; they influence every aspect of your health from your internal organs and immune system to your skin, hair and nails.

Many crash diets focus on eliminating certain food groups, in particular fats. Contrary to popular belief, healthy fats (monounsaturated and polyunsaturated) are a very important part of your diet. Certain nutrients are “fat-soluble”; this means you need some fat intake for your body to properly absorb vitamins.

The best way to guarantee you’re getting all the important nutrients you need is to eat a balanced diet with all the major food groups, including lots of fruit and vegetables. If you are worried about fat or carbohydrate intake, the best way to achieve a healthy body weight is to consistently reduce your portion sizes, aiming for an overall daily calorie deficit of around 300-500cal. Changes may take a little while longer to see, but the process is safer and results will last for longer.

Rabbit starvation

Rabbit starvation or “protein poisoning” is a hypothesised condition that occurs from the long term overconsumption of protein without any fats or carbohydrates. Though it is unrecorded in the present day, the condition highlights the dangers of completely eliminating food groups.

Individuals who have historically experienced this condition have become malnourished and died due to nutritional deficiencies; even when the correct amount of calories are consumed.

Heart damage

The heart is an organ that is particularly vulnerable to fad diets. In particular, those with pre-existing cardiovascular problems are at risk. If you have a history of heart disease or stroke, it is strongly recommended that you avoid low-calorie diets.

In 2018, a study using magnetic resonance imaging (MRI), found that though VLCDs significantly reduced overall liver, visceral and body fat - along with making improvements to blood pressure, cholesterol and insulin resistance - they increased heart fat content. After eight weeks of dieting, this heart fat content was reduced. However, for the preceding seven weeks they recorded heart muscle deterioration and increased difficulty pumping blood.

Researchers concluded that for individuals with pre-existing heart conditions, VLCDs pose an unnecessarily high risk. For individuals with “healthy” hearts, they should still exercise caution for the risk of exacerbating unknown cardio conditions.

How can I lose weight healthily?

Extreme dieting or exercising is not the route to take for healthy weight loss. You should instead focus on eating a healthy, calorie-controlled diet and exercising regularly (in moderation) to help you lose weight slowly, safely and sensibly. In turn, this will help you to maintain your weight loss.

Try to create routines for yourself which help you stick to a healthier lifestyle. Creating a diet plan can help you maintain a calorie deficit, whilst you may find it beneficial to set yourself exercise goals to achieve and maintain your fitness. This could involve signing up for a half-marathon and designing a training programme. Alternatively, try signing up for exercise classes with a friend or downloading an exercise app.

To calculate the number of calories you should consume on a daily basis, there are a number of online tools available. However, it is best to speak to a diet expert (preferably a dietitian over a nutritionist) or your doctor. The average basal metabolic rate (BMR) - how much you burn during rest - is around 1,400 calories for a woman and 1,800 calories for a man. Overall daily caloric expenditure is closer to 2,000 for a woman and 2,500 for a man. Although, as everyone is a different build and has a different activity level, this figure will vary.

As mentioned, the key to healthy weight loss and overall wellness is to gradually improve your eating habits and activity.

Medically reviewed by
Dr. Sarah Donald MRCGP DFSRH DPD DRCOG Written by our editorial team
Last reviewed 22-04-2023
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