Do Crash Diets Affect Weight Loss ?


During crash dieting (about <1000-1200 calories for women and <1600-1800 for men depending on body size) scales show that weight is being lost. However, in truth, body fat hasn’t decreased much and instead healthy muscle is lost. Furthermore, since about 1/3 of body weight is water, often much of the weight lost during crash diets is water, this is especially true for low carbohydrate diets. Once the body gets re-hydrated with water, the weight will come right back.


During crash dieting the starvation protection mechanism is often triggered. Since the body is driving all it can into fat cells, while simultaneously releasing little of what is held in the cells, the body needs to find energy from elsewhere to power your everyday physical activity (e.g. walking, working etc.) and acquires it by literally cannibalizing muscle and organ tissue to provide energy. This loss of muscle, in turn lowers metabolic rate so that the body needs fewer calories to keep ticking over and weight loss slows down. In response, some people on crash diets reduce their calories even further for the weight loss to continue. The more calories you cut, the more the body tries to hold on to its fat stores. The more often you crash diet and severely restrict your calorie intake without exercising, the more likely you’ll have a lot less muscle compared to the very first time you dieted.

As a consequence, it is likely that your metabolism is slower meaning that you need fewer calories to maintain your current weight. Even worse, when the weight goes back on, you usually only regain fat! This means, your metabolic rate is likely to have dropped a little every time you’ve crash dieted, making it slightly harder each time you go on a new diet to lose weight. It becomes a vicious circle. The only way to get out of starvation mode is to eat more.

Your body has further tricks up it’s sleeve to get energy and your brain triggers intense cravings and increases your appetite. So much so, that even the most strong-willed person would find it difficult not to succumb to binge eating or cheating on a crash diet. Your thyroid hormones (regulates metabolic rate) also decrease, leading to a further drop in metabolic rate, in order to conserve energy.

The starvation response explains why people experience such poor results with crash dieting, are unable to maintain any weight loss and worse still end up having a greater percentage of fat when they regain the weight they lost than when they first started their crash diet! Starvation mode will conserve energy by slowing down your metabolism, therefore destroying everything you are working to achieve. Once regular eating continues, your body will store calories as fat in order to survive the next time it goes without food. You gain more weight (all fat) than when you started. Of course, this response is a great solution if you’re in a famine situation. But if you’re trying to lose weight, it’s going to do little to help you shift those unwanted pounds and in fact will make things worse!


Your metabolic rate slows down, which means that you require less calories/ day. This means that weight loss slows down or stops. For weight loss to continue, you need to create a bigger calorie deficit, which means you’ve got to reduce your calories further, creating a vicious circle. Your body catches on, has started conserving energy and you hit a weight loss plateau.


95% of conventional dieters and crash dieters are unable to maintain weight loss. Some even experience additional weight gain. Possibly one of the worst effects of metabolic slowdown is that once you stop the diet and start to eat what used to be your normal daily maintenance level of calories, you may gain the weight you lost right back and some people put on even more. Since your metabolism has slowed down you require fewer calories than before you started the diet. This means that when you eat a normally you gain weight.


The weight gained back after crash dieting is fat. However, the weight lost during the crash diet was unlikely to have been 100% fat. This means that even if you have only put back on the same amount of weight you lost, you may still be worse off, because you have a greater amount of fat than what you started off with.


Research suggests that the body loses a disproportionately high amount of muscle during very low calorie intake and that this may suppress metabolism by up to 45 percent.

Crash Diet

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  1. Dieting 101: Starvation Protection Mechanism

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