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Quick Weight Loss: What Happens When You Crash Diet?

Emmie Satrazemis, RD, CSSD


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We’ve all seen the ads for weight loss programs promising 10 pounds of weight loss in a week or extreme weight loss in a month. And unless you’ve been living under a rock, you’ve probably also seen or heard of television shows, like the biggest loser, where contestants are losing insane amounts of weight quickly and shrinking before your eyes week after week. The thing is, these examples are not realistic for everyone and usually not sustainable in the real world. In fact, most biggest loser contestants gain the weight back after the show (1).

smashing cake gif diets dont work

Fast weight loss requires drastic measures. Contestants on these shows are typically working out for multiple hours each day and eating a very low calorie diet plan. Your weight loss efforts would basically become a full-time job. Do you have that kind of time and dedication? And how do you plan to keep it up long-term?

Can You Diet to Lose Weight Fast?

Well fast weight loss is possible. Crash dieting and starving yourself only works for a little while. And even if you are successful, you may end up gaining it all back once you go off the diet and have likely done some damage to your metabolism and lean muscle in the process.

i want a taco gif diet frustration

We all want fast results, and we also want it to be as easy and painless as possible. But what you should really ask yourself is: are you just looking to see the numbers on the scale drop as quickly as possible? Or are you looking to lose body fat, get in shape and get results that won’t disappear more quickly than they came?

What Happens When You Crash Diet?

Counting calories is the single most effective weight method (2). If you eat more calories than your body needs, you will gain weight, and vice versa. This is why pretty much every single diet that works uses some form of calorie control. Crash diets take this concept to extreme by cutting a large number of calories to shed pounds faster. 

The way this works is, calories provide the daily energy you need for survival. And when you cut calories below your energy needs, your body starts to compromise certain processes to keep on surviving. One of these compromises is weight loss.

cutting calories gif dieting

Ideally, your body will continue to losing weight until it reaches a new energy homeostasis and a new weight. But when you cut your calories too low through extreme dieting, your body has to continue to find new ways to compensate, and eventually you must either increase your calories to support life, or you start to face serious health complications.

Besides the fact that starving yourself is not a permanent, viable solution to survival or weight loss, there are other side effects to consider when you try to reduce weight too quickly. 

You're Constantly Hangry

Losing weight can affect your hunger, fullness hormones causing you to feel more hungry. And exercising can increase this even further. While going a little hungry can be helpful for weight reduction, being extremely hungry can be downright painful. If you can get past the constant hunger pains, you may also find that crash dieting is making you obsessed with food. Your body is so hungry that food becomes all you think about (3). 

hangry starving gif dieting

Being hungry all the time is bad enough, but very low calorie diets can cause you to be in a terrible mood as well. Calories, especially carbs, play a major role in regulating your emotions, and being so hungry that you are angry is a real thing. Carbohydrates are linked to your self-control - which is why we cannot control our temper when we have low blood sugar, and we get hangry. 

Your Metabolism Slows

slow metabolism gif diet

One of the ways your body compromises for starvation mode is by slowing your metabolism down - burning less calories per day ensures you will survive a little longer. While all low calorie diets can cause your metabolism to slow down a bit, existing in starvation mode for extended periods of time does some serious damage. After any weight loss, you will likely have a lower resting metabolism - meaning you will need to eat less calories per day to maintain your weight compared to a similar individual at the exact same weight who has never been on a diet (4). For most, this difference could be as little as a 5% decrease. But after crash dieting, this could drop to 15% or more, making it seem like you will have to be on a diet forever to maintain the weight loss. Slow and steady weight loss of 0.5 to 1% body weight per week is much easier to keep off.  

You Get Skinny Fat

If you aren't getting enough protein, and not strength training regularly, extremely restrictive diets can cause you to start burning more lean muscle for energy instead of fat (5). Why does this matter? You are losing precious muscle mass - which is key for keeping your metabolism intact and improves your overall quality of life.  In addition, reduced lean muscle mass increases your overall body fat percentage, even though the number on the scale is decreasing.

Muscle is more dense than fat, which can make you look leaner overall. Once you reach your desired weight, you may not feel as fit and toned as you would if you lost more fat and maintained your lean mass throughout the process. In order to decrease your body fat and get toned, you would have to gain muscle mass, essentially gain weight back, and try to lean out by burning fat. It is pretty counter-intuitive to lose weight from losing muscle weight just to try and gain back more muscle weight in the end. 

skinny fat muscle loss while dieting gif

Eating a high protein diet and strength training can help reduce some muscle loss, but opting for a more sustainable approach is your best bet for protecting your lean muscle and promoting more fat loss. 

Your Nutrition Suffers

The thing is your body isn't a calculator. And while it needs a daily dose of energy to keep surviving, it also needs proper nutrition to function properly. It is nearly impossible to get all the nutrients your body needs on a very low calorie diet, even if you're eating only healthy food. Minor deficiencies can create serious complications. Very low calorie diets have been linked to heart problems, dehydration, mental confusion, and decreased immune function (6). And starving yourself over longer periods of time can lead to heart attacks, impaired liver and kidney function, seizures and death (7,8,9,10)

poor nutrition gif

How to Lose Weight Fast the Healthy Way

If you are very overweight, there are some very low calorie diets out there that require medical supervision. But the success of these diets are still being studied and they may not be the answer.

healthy diet motivation gif

Your best bet for healthy rapid weight loss is to cut your calories by 15 to 20% and aim to lose 0.5 to 2 pounds per week, depending on your starting weight.  If you're not keeping track of how many calories you are eating each day, it is going to make losing weight much harder. Figure out how many calories you need to eat a day to reduce your weight and track your daily intake to match. Studies show tracking your food intake can help you lose up to twice as much weight (11)! And make sure you are also choosing the best foods for weight loss

Hang in there. Progress takes time and hard work. While you may not be able to get your dream body overnight, or in one week, you can still get your dream body by working hard and making your health a priority. 


Download the FREE Trifecta app to log your daily food intake and help keep yourself on track.  





1. Fothergill E, Guo J, Howard L, et al. Persistent metabolic adaptation 6 years after The Biggest Loser competition. Obesity (Silver Spring, Md). 2016;24(8):1612-1619. doi:10.1002/oby.21538.

2. Calories do count. Kinsell, Laurance W. et al. Metabolism - Clinical and Experimental , Volume 13 , Issue 3 , 195 - 204

3. Keys, A.; Brožek, J.; Henschel, A.; Mickelsen, O.; Taylor, H. L. Oxford, England: Univ. of Minnesota Press The biology of human starvation. (2 vols).(1950). xxxii 1385 pp.

4. Michael Rosenbaum, Jules Hirsch, Dympna A Gallagher, Rudolph L Leibel; Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight, The American Journal of Clinical Nutrition, Volume 88, Issue 4, 1 October 2008, Pages 906–912, https://doi.org/10.1093/ajcn/88.4.906

5. Vink, Roel & Roumans, Nadia & A. J. Arkenbosch, Laura & Mariman, Edwin & van Baak, Marleen. (2016). The effect of rate of weight loss on long-term weight regain in adults with overweight and obesity. Obesity. 24. 321-327. 10.1002/oby.21346.

6. European Society of Cardiology (ESC). (2018, February 2). Crash diets can cause transient deterioration in heart function. ScienceDaily. Retrieved March 15, 2018 from www.sciencedaily.com/releases/2018/02/180202123836.htm.

7.  https://www.sciencedaily.com/releases/2008/07/080708080738.htm.

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