LAW OF ENERGY BALANCE:
Weight loss = energy expended > energy consumed.
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To lose weight you must create a negative energy balance: calories taken are less than calories expended. Result: Fat, glycogen and muscle are used for energy to make up the caloric deficit and ideally weight is lost and fat stores are reduced. However, losing weight and losing fat are two different stories. Weight loss does not necessarily equal fat loss.
During crash dieting, i.e. low calorie weight loss programmes (<1200 calories for women and <1800 for men), 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.
CRASH DIETS: Starvation Protection Mechanism
The secret with any serious and long-lasting attempt at weight loss is to “trick” what is known as the starvation protection mechanism of the body. Crash diets more often than not, reduce food/ caloric intake to the point that the body believes that it is starving (<1200 calories for women and <1800 for men). This is because your body uses a brilliant primal survival system that is thought to have evolved over thousands of years as a defense against starvation and means the body becomes super efficient at making the most of the calories it does get from food and drink. When you are crash dieting your body does not know that there are a dozen restaurants and supermarkets around the corner and takes steps to protect it. Your body does not know the difference between starvation and crash dieting and little or no food for extended periods of time equals danger.
The main way your body responds to crash diets, is to protect its fat stores and instead use lean tissue or muscle to provide it with some of the calories it needs to keep functioning. Fat is the body's energy reserve and when you consume fewer calories than your body needs, your body turns to fat for energy. However, when your body feels threatened (crash diet) the body's leptin levels (a hormone that liberates stored body fat) decrease and only allows fat cells to release energy in order to sustain your most basic bodily functions. This means that although you are dieting, you are not losing fat (or losing only a small proportion of fat) because your body has shut down is its fat-burning ability in order to preserve energy. To make matters worse, when you eat your body starts to store the nutrients/ energy in your fat cells (as a calorie reservoir) for later use, rather than using it to provide energy for your normal day-to-day activities. This means that your fat cells may be increasing in size, instead of getting smaller. The bottom line is that your body fat may actually be INCREASING!
CRASH DIETS: Muscle Loss and Fat Gain
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 also lower 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 for you 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.
This 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!
The significant weaknesses of conventional crash diets are:
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