Perhaps the question that dietitians get asked the most frequently is: “What do you think about the *insert fad diet here* diet?” As an RD, I typically do my best to change the subject because I’ve learned my lesson. (Like the time I gave my hairstylist my very honest opinion regarding an *unnamed* diet only for her to tell me that she planned to start that diet the following week … I’m getting my haircut elsewhere now) Instead of changing the subject, this time I’ll take an evidence-based, unbiased look at some of the most popular diets. I’m calling it: A Dietitian’s Guide to Fad Diets. 

First up… Paleo

What it is: “A nutritional approach that focuses on eating only foods that are high in nutrients, unprocessed, and based on the foods that were available and eaten by humans in Paleolithic times” (


  • Includes a variety of fruits and vegetables 
  • Focuses on whole foods rather than processed goods
  • Limits overly salty/sugary foods


  • Can lead to a restrictive mindset surrounding “clean” eating 
  • Low in fiber, as grains and legumes are not included 
  • Low in calcium, as dairy is not included
  • Easy to over-consume protein and fat 

Ketogenic Diet 

What it is: Originally designed to help manage epilepsy, this diet is characterized by high fat, moderate protein, and low carbohydrate (< 50 grams/day) intake. The goal is for the dieter to achieve ketosis, a state in which the body is burning fat in place of carbohydrate as an energy source. 


  • Focuses on whole foods rather than processed goods 
  • Includes healthy fats like avocado and olive oil 


  • Limits higher-carbohydrate fruits and vegetables 
  • Not enough evidence to show the long-term impacts of following this diet
  • Low in fiber, as whole grains, legumes, and starches are off-limits
  • Is fairly restrictive and difficult to maintain 
  • Initial rapid weight loss of water weight is often followed by a regain when dieter returns to eating carbohydrates 

Vegetarian/Vegan Diet

What it is: The vegetarian diet focuses on plants for food. Lacto-ovo vegetarians still consume dairy products and eggs, lacto vegetarians consume plant foods and dairy products, and vegans consume plant foods only. 


  • Includes a variety of fruits and vegetables 
  • Includes a variety of whole grains 
  • Less environmental impact 
  • Studies show this diet reduces risk of heart disease, diabetes, and some cancers


  • Potential to be deficient in protein, calcium, zinc, and B12 
  • Vegan diet in particular is restrictive
  • More thoughtful planning is required to ensure you are getting all the nutrients your body needs (e.g. Oreos are vegan but provide no nutritional benefit) 

Mediterranean Diet 

What it is: This diet is “a way of eating based on the traditional cuisine of countries bordering the Mediterranean Sea. While there is no single definition of the Mediterranean diet, it is typically high in vegetables, fruits, whole grains, beans, nut and seeds, and olive oil.” (


  • Includes a variety of fruits and vegetables 
  • Promotes whole grains and fiber 
  • Is flexible and easy to follow, as there are no truly “off-limits” foods
  • Studies show this diet reduces risk of heart disease
  • Allows red wine in moderation (okay this a subjective one, but I’m for it!) 


  • Fresh fish (which is recommended twice per week) may be difficult for some to access 
  • Some people may want or need more structure than this diet provides

So… if all of these diets were ranked, where would they land? 

I’m so glad you asked! The U.S News & World Report did the heavy-lifting for us with tons of studies and research to back their “2020 Best Diets Overall” report. Read it for yourself, or let me just give you the quick review:

#1 – Mediterranean Diet
#9 – Vegetarian Diet 
#17 – Vegan Diet 
#29 – Paleo Diet 
#34 – Ketogenic Diet 

The bottom line: we don’t need to follow a particular “diet” in order to eat healthy and live well. There are lots of different paths to health, so the best thing you can do is team up with a professional to find what works for you. 

CLICK HERE to get started with your FREE Assessment!