Extreme weight loss diets and why you should stay away from them

Steve Silvestro, MD - Contributor Avatar

Written by Michael Martin 

Steve Silvestro, MD - Contributor Avatar

Written by Michael Martin 

last updated: Mar 19, 2021

4 min read

Starvation, avoiding food groups—these behaviors aren’t exactly the hallmarks of a healthy lifestyle. Nevertheless, extreme weight loss diets have become a major industry among people who want to drop pounds fast. Here, we'll break down the most popular extreme diets, and how they can be dangerous.

Weight loss

Fad diets stop here

If appropriate, get effective weight loss treatment prescribed for your body.

Fad diets stop here
Fad diets stop here

What is an extreme weight loss diet?

An extreme diet is one that's intended to make the dieter lose a large amount of body weight in a short amount of time, usually by severely restricting calories. Some of these diets promise being able to lose 10 pounds in a matter of days or 30 pounds in a month. 

When something sounds too good to be true, it usually is, and many of these diet plans can have harmful side effects. They can not only put your health at risk, but can also throw your weight loss journey seriously off the track. 

Here are some popular extreme weight loss diets:  

Very low-calorie diets

These diets drastically restrict the number of calories consumed in a day. In some cases, that can be as low as 600 to 800 calories. It’s recommended that the average man consume 2,500 calories daily to maintain weight, or 2,000 if they want to lose one pound a week. The average woman should consume 2,000 calories daily to maintain weight, or 1,500 if they want to lose one pound a week. These recommendations may differ depending on the specific lifestyle and characteristics of the person. (Osilla, 2020).

Very low calorie (VLC) diets are hard to maintain, and you’re likely to regain any weight you lost as soon as you stop the diet. Ironically, at least one study found that restricting calories elevates the body's levels of cortisol, the stress hormone that tells the body to hang on to fat, particularly around the belly (Tomiyama, 2010).

Low carb/high fat

Diets like keto and the Atkins diet encourage eating as few carbohydrates as possible and consuming high amounts of dietary fat. The goal is to force the body to burn fat for energy instead of carbs. 

These diets can cause high initial weight loss, but the loss is mostly water (Joshi, 2018). And it’s hard to stick with these diets because they're highly restrictive. In U.S. News & World Report's annual Best Diets roundup, keto was ranked 37th out of 39 diets for overall quality and last in the "best diets for healthy eating" category (U.S. News, n.d.).


Intermittent fasting has become a buzzword, and some research has shown that it can have some health benefits, including a positive impact on weight loss and overall wellness. That's different from a starvation diet, during which participants try to eat as little as possible for as long as possible. Starvation diets have a number of potentially dangerous side effects, from heart issues to muscle loss and malnutrition (Osilla, 2020).


Fruits and vegetables are necessary parts of a healthy diet, but man is not meant to live on their juice alone. During a juice cleanse, dieters consume only fruit or vegetable juices for several days. This regimen lacks important nutrients, such as fiber and protein. 

"Juicing or detoxification diets tend to work because they lead to extremely low caloric intake for short periods of time, however tend to lead to weight gain once a normal diet is resumed," wrote authors of a study of popular diets in the journal Nutrition and Obesity (Obert, 2017).


"Detox" diets claim to help your body rid itself of toxins. But not only are detox diets unnecessary—our liver and kidneys do a great job of detoxing the body all on their own—there's also little to no evidence they're effective for weight loss (Klein, 2015).

Liquid protein

This diet fad blew up in the mid '70s. Dieters consumed nothing but a liquid protein drink for several weeks, totaling 400 to 800 calories a day. Some people lost a lot of weight (calorie restriction tends to do that). But by 1979, the diet faded from popularity when it was revealed that at least 17 people had died of heart attacks while on the diet (Isner, 1979). 

Dangers of extreme weight loss diets

As you can see, many extreme weight loss diets don’t even work as intended. To make matters worse, they come with some serious potential complications. 


Some extreme diets lack the full complement of nutrients the body needs to function. Over time, that can lead to malnutrition. When you don't consume enough calories to keep the body running, it enters into survival mode, slowing metabolism and trying to hold on to every fat cell it can. Eating too few calories can lead to cognitive difficulties, organ damage, and even cardiac arrest (Osilla, 2020). 

Bone loss

Studies show that a high-meat diet that is low in fruits and vegetables—like one might undertake on the keto diet—can lead to bone loss (Joshi, 2018).  

Yo-yo dieting

Extreme diets tend to lead to weight loss and regain; when this is done repeatedly, it becomes "yo-yo dieting" (or "weight cycling"), which comes with risks. According to a 2017 study, it can lead to high blood pressure and cause fluctuations in heart rate and cardiac workload, potentially damaging the heart (Rhee, 2017). 

Heart problems

When weight loss happens too fast, the muscles of the heart can atrophy, leading to potentially fatal arrhythmias or heart attacks (Osilla, 2020).

Muscle loss

Calorie-restrictive diets lead to a loss of muscle mass throughout the body, making the remaining muscles weaker and slowing the resting metabolic rate, which can slow your future weight loss (Weiss, 2017). 

Insulin resistance

Yo-yo dieting increases the risk of developing insulin resistance and type 2 diabetes (Li, 2018).

Slowing metabolism

Research shows that rapid weight loss can slow your metabolism. One study tracked the most extreme dieters of all: Contestants on The Biggest Loser, who had quickly lost massive amounts of weight. Researchers found that their metabolisms slowed to adapt to their new weight. But when the contestants regained weight, their metabolisms didn't speed back up to compensate (Fothergill, 2016). 

Make healthy lifestyle changes instead

Extreme weight loss diets can sound very appealing, especially if you’re looking to drop more than just a few pounds. The problem is these diets can be dangerous, and they often don’t even work as promised—certainly not long-term. 

If you’re looking to lose weight, it’s a much better idea to do so by making healthy and sustainable changes to your lifestyle. You probably won’t lose weight as rapidly, but as they say, slow and steady wins the race. Experts recommend 1–2 pounds per week as a safe and healthy goal for weight loss (NIH, n.d.). 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

  • Fothergill, E., Guo, J., Howard, L., Kerns, J. C., Knuth, N. D., Brychta, R., Chen, K. Y., Skarulis, M. C., Walter, M., Walter, P. J., & Hall, K. D. (2016). Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity, 24 (8), 1612–1619. doi: 10.1002/oby.21538. Retrieved from https://pubmed.ncbi.nlm.nih.gov/27136388/

  • Isner, J. M., Sours, H. E., Paris, A. L., Ferrans, V. J., & Roberts, W. C. (1979). Sudden, unexpected death in avid dieters using the liquid-protein-modified-fast diet. observations in 17 patients and the role of the prolonged Qt interval. Circulation, 60 (6), 1401-1412. doi:10.1161/01.cir.60.6.1401. Retrieved from https://pubmed.ncbi.nlm.nih.gov/498466/

  • Joshi, S., & Mohan, V. (2018). Pros & cons of some popular extreme weight-loss diets. The Indian Journal of Medical Research, 148 (5), 642–647. doi: 10.4103/ijmr.IJMR_1793_18. Retrieved from https://pubmed.ncbi.nlm.nih.gov/30666989/

  • Klein, A. V., & Kiat, H. (2015). Detox diets for toxin elimination and weight management: a critical review of the evidence. Journal of Human Nutrition and Dietetics: The Official Journal of the British Dietetic Association, 28 (6), 675–686. doi: 10.1111/jhn.12286. Retrieved from https://pubmed.ncbi.nlm.nih.gov/25522674/

  • Li, X., Jiang, L., Yang, M., Wu, Y. W., & Sun, J. Z. (2018). Impact of weight cycling on CTRP3 expression, adipose tissue inflammation and insulin sensitivity in C57BL/6J mice. Experimental and Therapeutic Medicine, 16 (3), 2052–2059. https://doi.org/10.3892/etm.2018.6399. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6122336/

  • National Institutes of Health. Key recommendations. (n.d.). Retrieved March 18, 2021 from https://www.nhlbi.nih.gov/health/educational/lose_wt/recommen.htm

  • Obert, J., Pearlman, M., Obert, L. et al. (2017). Popular Weight Loss Strategies: a Review of Four Weight Loss Techniques. Current Gastroenterology Reports, 19 (12), 61. doi: 10.1007/s11894-017-0603-8. Retrieved from https://pubmed.ncbi.nlm.nih.gov/29124370/

  • Osilla, E.V., Safadi, A.O., Sharma S. Calories. [Updated 2020 Aug 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK499909/

  • Rhee, E. J. (2017). Weight Cycling and Its Cardiometabolic Impact. Journal of Obesity & Metabolic Syndrome, 26 (4), 237–242. doi: 10.7570/jomes.2017.26.4.237. Retrieved from https://pubmed.ncbi.nlm.nih.gov/31089525/

  • Tomiyama, A. J., Mann, T., Vinas, D., Hunger, J. M., Dejager, J., & Taylor, S. E. (2010). Low calorie dieting increases cortisol. Psychosomatic Medicine, 72 (4), 357–364. doi: 10.1097/PSY.0b013e3181d9523c. Retrieved from https://pubmed.ncbi.nlm.nih.gov/20368473/

  • U.S. News & World Report. Best Diets: Keto diet (n.d.). Retrieved February 26, 2021, from https://health.usnews.com/best-diet/keto-diet

  • Weiss, E. P., Jordan, R. C., Frese, E. M., Albert, S. G., & Villareal, D. T. (2017). Effects of Weight Loss on Lean Mass, Strength, Bone, and Aerobic Capacity. Medicine and Science in Sports and Exercise, 49 (1), 206–217. doi: 10.1249/MSS.0000000000001074. Retrieved from https://pubmed.ncbi.nlm.nih.gov/27580151/

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

March 19, 2021

Written by

Michael Martin

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.

Get access to weight loss medications, if prescribed.

Start now