By Natalia Walczak, Nutrition Student Intern St. Louis University (edited by Monika Jacobson, RDN)

Paleo, keto, and vegan diets are buzzwords very familiar to most people and especially Registered Dietitians. People are becoming increasingly health conscious as research develops about how our diet affects our health. Everyone is trying to figure out the “healthiest” way to eat and it’s certainly confusing. Weight loss diets such as Atkins and South Beach have long been debunked as unhealthy and extreme fads. With more media influence, diet culture is in our faces like never before. Are these popular (sometimes trendy) diets healthy or are they just another passing fad? Let’s take a look at 5 common examples.

  1. Low FODMAP diet

Traditionally used by dietitians to treat IBS, the low FODMAP diet has recently gained popularity in mainstream diet culture. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are all carbohydrates that are sometimes poorly absorbed by the body and may trigger gastrointestinal distress in certain individuals (especially in irritable bowel syndrome). Low FODMAP is an elimination diet that occurs in three stages (if clinically observed). In the first phase, the person eliminates all high FODMAP foods for a period of 2-6 weeks. Next, each FODMAP subgroup is reintroduced methodically and symptoms are observed to determine which groups trigger symptoms. People suffering from IBS are often sensitive to some but not all subgroups and the last phase customizes a long-term diet that eliminates the specific foods that are not tolerated. Although the diet has shown to be effective as a medical nutrition intervention for those with IBS, it is not a weight-loss or health-conscious diet. Because it eliminates so many nutrient-dense foods at first (many of the foods that are on the FODMAP list are “healthy” fruits and vegetables), it is important to remember that it is not a long-term diet change but rather a tool to identify trigger foods. In addition, it is important to implement the diet under the supervision of a Registered Dietitian to maintain a healthy nutritional status throughout.

  1. Mediterranean Diet

Inspired by the eating habits of Spain, Italy and Greece, the Mediterranean diet has shown to be increasingly promising in improving overall health, particularly heart health. Largely plant- based, the diet emphasizes daily consumption of fruits, vegetables, whole grains, and healthy fats, such as olive oil. Moderate amounts of seafood, poultry, eggs, and dairy are recommended, while red meat is only eaten occasionally. Foods such as added sugars, refined grains, trans fats, and processed meats are avoided. An overview of research on the Mediterranean Diet concluded that coupled with regular physical activity and not smoking, over 80% of coronary heart disease, 70% of stroke, and 90% of type 2 diabetes can be avoided by healthy food choices that are consistent with the traditional Mediterranean diet (Willett, 2006). The Mediterranean diet is recommended by Registered Dietitians because it promotes a healthy lifestyle without being restrictive and can be beneficial to everyone!

3. Paleo

On the flipside, the Paleo diet is a meat-heavy diet, promoted as a way to improve health. The eating pattern follows what would have been eaten by our ancestors during the Paleolithic era, theorizing that our body is more genetically matched to eat like cavemen. Paleo is a low-carb diet that emphasizes lean meats, fruits, vegetables, nuts, and seeds. It eliminates grains, legumes, dairy, refined sugars, and processed foods. Although the Paleo diet contains elements of a healthy diet such as high levels of fruits and vegetables, it eliminates many food groups that we know are beneficial to our health. Whole grains and legumes are high in fiber, vitamins, and minerals while low-fat dairy products provide us with a good source of calcium and protein. Like with any restrictive diet, Paleo may result in some initial weight loss, but there is little evidence to show that it has long-term benefits and some studies link it with an undesirable lipid profile (i.e. high cholesterol due to the high levels of saturated fat). Because it eliminates entire food groups and promotes an unbalanced consumption of macronutrients, many Registered Dietitians have expressed concern about the fad diet. Much stronger research simply promotes a slight calorie deficit for effective weight loss without eliminating any one food group. Most dietitians will tell you that moderation is all you need for a healthy lifestyle; eat lots of fruits, vegetables and whole grains but don’t worry about having some steak or a cupcake once in a while.

4. Blood Type Diet

Introduced in the 1996 by Dr. Peter D’Adamo, the Blood Type Diet asserts that the foods you eat should depend on your blood type. This diet has come and go in popularity. These recommendations include:

Type O- diet high in protein/meat, fruits vegetables and low in gluten, dairy and legumes

Type A- organic vegetarian diet

Type B- diet including both plants and vegetables with some dairy; low in wheat, corn, lentils, tomatoes

Type AB- high in seafood, dairy, tofu, beans, and grains

Sounds intriguing right? However, after reviewing over 1,400 related studies, it was concluded that there is no evidence to support the claims of the Blood Type Diet. Although some may swear by it, any potential benefits are likely caused by the increased consumption of whole foods in general, which we already know are good for us, and not an actual relationship between our blood type and our diet. Notice that all four of these diets have one thing in common: they promote unprocessed, low-fat, plant-based foods which are good for our health no matter our blood type.

5. Intermittent Fasting

Perhaps the most popular fad diet of them all, intermittent fasting has swept through the world of nutrition and fitness in recent years. Used for weight loss or health improvement, the eating pattern cycles through periods of eating and fasting. Some popular methods include:

  • 16/8 fasting: Eating within a period of 8 hours (such as 11 am to 7 pm) and then fasting for 16 hours
  • Eat Stop Eat: Fasting for 24 hours once or twice a week
  • 5:2 diet: Consuming 500-600 calories on two nonconsecutive days of the week and eating normally the other five days.

Research has shown promising results about the impact of intermittent fasting on chronic disease development, weight loss, overall health, and longevity. Evidence shows that intermittent fasting is not harmful to us both physically and mentally. However, it is important to remember that intermittent fasting is not for everyone. Effects of fasting on sleep and physical activity have not been extensively studied. Fasting for long periods of time can also lead to binging episodes during eating periods and result in disordered eating patterns. Because it is such a regimented way of eating, it is important to consult with a dietitian while deciding to implement intermittent fasting into your lifestyle.

Diet culture is a strong force in our society. As research teaches us more about how diet affects our health, new diets will continue being developed. Whether you are trying to lose weight or just be more health-conscious, be weary of new fad diets. Seemingly “evidence-based”, many of these trendy ways of eating can actually be very harmful to our health. One of the biggest red flags of any diet is cutting out any food group entirely. Remember, there is no secret to being healthy and moderation is the most important thing to keep in mind. And if you are not sure about something, always talk to a Registered Dietitian.


Willett, W. (2006). The Mediterranean diet: Science and practice. Public Health Nutrition, 9(1a), 105-110. doi:10.1079/PHN2005931