What is a crash diet?

Caroline J. Cederquist, MD
Family Medicine
A crash diet is one that focuses on limited intake of calories for quick weight loss results, often omitting whole food groups. There is no magic pill or quick fix to losing weight, including these crash diets that focus on 1,000 calories or less.  When your body does not have enough calories and energy to perform daily functions, your metabolism will instinctively go into starvation mode or “fight or flight” mode.  At this stage, your body can begin to store every calorie it can as fat in order to survive.

Eating a proper diet balanced in lean protein, healthy fats and complex carbohydrates gives your body the fuel it needs to function properly.
The MD Factor Diet: A Physician’s Proven Diet for Metabolism Correction and Healthy Weight Loss

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The MD Factor Diet: A Physician’s Proven Diet for Metabolism Correction and Healthy Weight Loss

Are you finding that weight is easy to gain and hard to lose? It’s not your fault!Over 89 percent of people struggling to lose weight have a metabolism dysfunction called the MD Factor. That’s approximately 150 million Americans suffering from this condition, and most do not even know it. The breakthrough concepts in The MD Factor Diet isolate metabolism dysfunction as the reason why millions of Americans cannot succeed in losing weight. Over the course of your lifetime, changes occur in your body’s chemistry that can reverse your ability to lose weight. There’s a way to reclaim your health: the doctor–approved plan detailed in this book.The MD Factor Action Plan outlined by Dr. Caroline J. Cederquist helps you:Correct metabolism for lifetime weight lossImprove cholesterol and blood pressureEnhance sleep quality and boost energyReduce cravings for sweets and starchesRegulate blood sugarDr. Cederquist will help you identify whether you have metabolism dysfunction and also give you the proper action plan to reverse it—with quick results. Achieve a more energized, lighter, and healthier you in just two weeks with The MD Factor Diet.
Natasha Turner, ND
Alternative & Complementary Medicine
To add to the previous answer, there are a number of reasons why you want to avoid a crash diet: potential loss of muscle, lower thyroid function and increased cortisol. Here's the scenario: You have 10 days until your beach vacation. What do you do? Slash the calories, live on a liquid diet, up the exercise and hope for the best, right? After all, how much damage can that low-calorie diet do? Well, a classic study from the Journal of Clinical Endocrinology & Metabolism discovered that fasting resulted in a 53 percent reduction in serum T3 levels (your active thyroid hormone that increases metabolism) and a 58 percent increase in reverse T3 (RT3) levels, which block thyroid hormone.

On a given day your liver converts T4 (the less active thyroid hormone, thought of as a storage hormone) to RT3 as a way of getting rid of the excess. In a low-calorie situation, where your body needs to conserve energy, the percentage may spike significantly, and (based on the study above) it’s common to find yourself converting 50 percent or more of your essential thyroid hormone into metabolic waste. On a starvation diet you also experience a significant increase in cortisol. The acute stress activates this surge because your body is under the impression that there’s less food available. Bottom line: Avoid starvation diets and be sure to throw in a weekly or bi-weekly cheat meal to keep your metabolism revving.

Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
Crash diets cut calories drastically. They often restrict entire food groups as well. Such diets can result in rapid weight loss, although that weight is mostly water. That's because to the body a crash diet feels like being starved, and its reaction to starvation is to release water. As soon as you start eating normally again, the water—and the weight—will return.

Beware of any diet that drastically cuts calories, forbids entire food groups (like fruits or grains), includes pills or potions, advises that you eat foods only in certain combinations or tells you to skip meals. In the long run, crash diets won't help you lose weight and keep it off.