Extreme weight loss diets: are they safe?

Starvation, avoiding entire food groups, lack of pleasure found in food—these behaviors aren’t the hallmarks of a healthy relationship with eating (unless specifically recommended by a healthcare provider). Nevertheless, extreme weight loss diets have become a major trend among people who want to drop pounds fast. But beware of diets that make lofty promises like, “Lose 30 pounds in 30 days!” These diets are often unsafe and unregulated. Continue reading to learn more about popular extreme diets, and how they can be dangerous.

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–at least two pounds per week on an ongoing basis, which can be more than most experts say is safe to lose each week. These measures typically fall into a few main categories:

• Diet pills and supplements 

• Starvation diets

• Very low-calorie diets (VLCDs)

• Creams, patches, and other devices

When something sounds too good to be true, it usually is. Many of these diet plans can have harmful side effects. Not only can they put your health at risk, but they can also throw your weight loss journey off track in the longer term. Here’s what you should know about some extreme weight loss diets:

Very low-calorie diets (VLCDs)

Very low-calorie diets (VLCDs) drastically restrict the number of calories consumed in a day. In some cases, daily calorie consumption is as low as 600 to 800 calories. 

To put that in perspective, experts recommend that the average biological man consume 2,500 calories daily to maintain weight, or 2,000 if they want to lose one pound a week. Similarly, experts recommend most biological women consume 2,000 calories daily to maintain weight, or 1,500 if they want to lose one pound a week.

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. 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.

Low carb/high-fat diets

Diets like the keto diet 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. These diets are highly restrictive, so it’s hard to sustain them long-term. Moreover, these diets can have adverse effects such as kidney stones and an increased risk of heart disease.

Diet pills and supplements

Non-prescription diet pills and supplements, often marketed as quick fixes for weight loss, pose significant dangers due to their lack of regulation by the Food and Drug Administration (FDA). Unlike prescription medications, these products don’t have to undergo testing before hitting the market. Many over-the-counter diet pills and supplements were found to contain harmful ingredients that can lead to serious health issues, including heavy metals, anabolic steroids that can cause liver damage and severe heart problems, and more.

Fasting

Intermittent fasting is an eating pattern that alternates between periods of eating and fasting, focusing on when you eat rather than what you eat. Common methods include the 16:8 method, where you fast for 16 hours and eat within an 8-hour window, and the 5:2 method, where you eat normally for five days and significantly reduce calorie intake for two non-consecutive days. Before starting any diet involving fasting, you should discuss with your healthcare provider. Some underlying healthcare conditions such as diabetes might make it dangerous to make drastic changes in your diet.

Intermittent fasting is 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 electrolyte abnormalities (that can have various downstream effects) and, in the longer term, heart issues,muscle loss, and malnutrition.

Juicing

Fruits and vegetables are necessary parts of a healthy diet, but people aren’t 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.

Detox

"Detox" diets claim to help your body rid itself of toxins. But not only are detox diets unnecessary—for the most part, 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.

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. 

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

Malnutrition

Many extreme diets deprive the body of the nutrients it needs to function. Over time, this can lead to malnutrition. When you don't consume enough calories to keep the body running, the body enters into survival mode, slowing metabolism and trying to hold on to every fat cell it can. Eating too few calories can also lead to cognitive difficulties, organ damage, and even cardiac arrest. 

Bone loss

Studies show that diets high in meat and low in fruits and vegetables—like the keto diet—can lead to bone loss. This can happen even after following the diet for 3.5 weeks. Research suggests the keto diet can impair normal processes of bone modeling and remodeling, which are essential for bone health. 

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, this can lead to high blood pressure and cause fluctuations in heart rate and other cardiovascular risk factors,potentially damaging the heart. 

Heart problems

Consuming too few nutrients can cause an electrolyte imbalance leading to potentially fatal arrhythmias or heart attacks. Nutritional deficiencies in compounds like thiamine over time can lead to significant heart problems. 

Muscle loss

Calorie-restrictive diets can lead to a loss of muscle mass throughout the body, weakening the remaining muscles and slowing the resting metabolic rate, which can slow future weight loss. By losing weight at a healthy pace and adding resistance training to your routine, you can help avoid muscle loss as you shed fat.  

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. 

Extreme weight loss may sound appealing, but at best, these diets don’t work. At worst, they’re dangerous. Instead, it’s better for your health to embrace safe and sustainable lifestyle changes to achieve and maintain a healthy weight. A balanced diet rich in whole foods such as fruits, vegetables, lean proteins, and whole grains provides essential nutrients and supports overall health. Regular physical activity, including both aerobic exercises and strength training, boosts metabolism and enhances physical and mental well-being.

You probably won’t lose weight as rapidly as extreme measures, 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, though of course this can vary depending on your personal circumstances. Consult a healthcare provider to create a personalized, safe weight loss plan.

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Current version

June 26, 2024

Written by

Michael Martin

Fact checked by

Raagini Yedidi, MD

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About the medical reviewer

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.