Juice cleanses, Atkins, Paleo, Keto, Intermittent Fasting, South Beach, Whole 30… Fad diets are practically their own language.

They promise quick weight loss and other results, which can be tempting to many young people. After all, our culture emphasizes the need to look a certain way, and when we don’t meet those impossible standards our self-esteem can take a nose dive.

The promises of fad diets can be seductive, but they’re not always true. Sometimes, they can actually be harmful (especially to teens who are still growing). Here, I “decode” three fad diets so you can see whether they’re actually as healthy as they claim.

1. Juice Cleanse

What is it?

Juice cleansing is marketed as a “detox” diet that lasts from a few days to several weeks. On a juice “cleanse,” you’ll consume fruit and vegetable juices… and nothing else.

How effective is it?

You may lose weight quickly at first since you’re consuming way fewer calories than you normally would. But unfortunately, those results won’t last, and it’s not healthy in the long run.

The Catch:

  • Your body won’t get the calories and nutrients it needs. This diet gives you nearly no proteins or fats, and lots of sugar without the healthy fiber.
  • You may feel hangry, sluggish or distracted by constant thoughts of food.
  • Your metabolism will slow down. This is your body trying to conserve energy, and it’s a natural response to starvation.
  • It doesn’t last. Once you stop the diet and start eating normally again, your weight will come right back.
  • There’s no actual “detox” or “cleansing” going on. Your liver already does a great job filtering out toxins!
  • Extremely restrictive diets like this one are NOT recommended for children or teens. It can hurt your mental and physical development.

If you want to reboot your diet without the downsides of detoxes and cleanses, eat more whole fruits and vegetables! You’ll find it surprisingly satisfying to chew your food instead of sipping it.

2. Ketogenic Diet (Keto)

What is it?

Keto was originally designed for children with epilepsy or certain metabolic disorders—not for weight loss. This diet mimics the effects of starvation (yes, you read that right) and is extremely low-carb and high-fat. Here’s how it works: your body breaks down carbohydrates into glucose. This is what your body usually uses for energy. When you eat very few carbs, your body will go through the glucose it has left pretty quickly. When your body doesn’t have any glucose, it burns fat instead. This is a state called “ketosis.”

How effective is it?

It can be very effective for weight loss—if you can stick with it.

The Catch:

  • Extremely restrictive diets like this one are NOT recommended for children or teens.
  • This diet takes a LOT of self-control and work. Most people have a hard time sticking with it, and go back to their pre-diet eating habits before long.
  • In the long term, it can be harmful to your liver and kidneys.
  • You may find you have less energy, or experience flu-like symptoms like nausea, vomiting, headache, fatigue, dizziness and constipation.
  • The Keto diet isn’t safe for everyone. If you really want to try this one, check with your doctor!

3. Intermittent Fasting

What is it?

This diet isn’t about what you eat, but HOW you eat. You fast for 16 hours, then eat “normally” during an 8-hour window. You can choose to do intermittent fasting just one day a week, three days a week, on the weekends, or every day.

It’s important to eat a balanced diet of whole foods from all food groups (starch, protein, fruits, vegetables and healthy fat) instead of filling up with junk food during the hours you’re not fasting.

This diet is not meant to encourage bingeing. As always, be mindful when you’re eating. Listen to your body and honor the hunger/fullness signals it sends you.

How effective is it?

Intermittent fasting has gained popularity over the past decade because of its weight loss claims. Some studies suggest that intermittent fasting is a promising weight loss strategy. However, those studies have been small, and there isn’t enough evidence to verify the claims.

The Catch:

  • You may have less energy or find it hard to concentrate when you’re fasting.
  • Some people binge or over eat during the “feeding” period. If you are prone to binge eating, or find yourself binge eating after starting intermittent fasting, this diet is not for you.
  • You could gain weight if you eat more calories than you normally would during the period where you eat.

The Bottom Lines

Healthy eating is a life-long practice, not a “quick fix.” It’s also about so much more than weight loss!

There is no such thing as “bad” foods. Eating should be joyful and nourishing, not anxiety-producing or all about denial! Starting healthy habits (whether your goal is to lose weight or not) doesn’t have to be super complicated or stressful. Check out the Mediterranean diet, a well-balanced diet with lots of whole grains, vegetables, beans, nuts, olive oil, fish and smaller amounts of dairy and poultry. You can also check out these six healthy eating tips for teens  and these 10 practices for healthy living.

If you’re 10-21 years old and live in NYC, you can make an appointment at the Mount Sinai Adolescent Health Center for free, comprehensive, non-judgmental health services including nutrition counseling and our free fitness program, Teen Fit!


May Chen, MS is a Dietetic Intern with Teachers College, Columbia University. She is a Registered Dietitian in Taiwan and holds a Master’s degree in Human Nutrition from Columbia University. May believes that in addition to learning how to make better food choices, keeping a healthy relationship with foods is fundamental to our overall well-being. She has a particular interest in child nutrition as she believes that an individual’s eating preferences and habits are established early in life.

The Mount Sinai Adolescent Health Center is located in New York City. It provides comprehensive, confidential, judgment free health care at no charge to over 10,000 young people every year. This column is not intended to provide medical advice, professional diagnosis, opinion, treatment or services to you or to any other individual, only general information for education purposes only.