From Paleo to Blood Type, A Doctor Vets Popular Diets

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Remarkably, everyone you know has become an expert on nutrition in the past year. There’s the friend who heard about something her brother’s girlfriend’s mom tried (she lost 80 pounds in five minutes!); the friend who once read that carbs give you vocal nodes so she faithfully abstains; the pal who swears by an all-beef-and-water regimen and the one who switches from vodka to tequila to moonshine each time a new study’s released. Erm, k. To put it politely, there is a new expert in town!

Meet Dr. Robin Berzin, Columbia-trained MD, founder of Parsley Health and friend of MR. Today, she’ll be breaking down the diets your friends keep telling you about (the ones that all the celebrities do and Instagram touts) — Paleo, GAPS, FODMAPs, Blood Type, Ketogenic and AIP. She’ll explain the point of each one, and whether or not it actually works. Already like, “What?” Great! Same! Let’s read on then, shall we?


What is it? The Paleo diet is a based on only consuming the types of foods eaten by early humans before mass agriculture, such as meats, vegetables, fruits and fish. Paleo is free of grains, legumes, dairy and sugar. Think of it as the classic hunter/gatherer diet.

The claim: This is the way our ancestors ate, and therefore the diet we are genetically and biologically programmed to thrive on.

The truth: The ancestral argument is tough to prove. People’s ancestors came from different places — some were probably more vegetarian, others lived off of the sea while still others foraged vegetables and hunted meats.

That said, the paleo diet is highly effective for weight loss and blood-sugar control because you effectively eliminate all refined carbs and sugar, which nearly everyone eats too much of today.

There are a lot of diseases and syndromes, from polycystic ovarian syndrome to diabetes, metabolic syndrome and even chronic yeast infections, that paleo has been shown to improve.

The downsides of this diet are that a lot of people end up eating large quantities of low-quality, industrially produced, hormone and antibiotic-laden animal products that can be inflammatory. They often don’t drink enough water to compensate for the increased protein intake and get constipated. They also tend to eat too few veggies so they are low on antioxidants and fiber, which are essential for colon health, heart health and cancer prevention.

I see patients all the time who are excited about going paleo. Our doctors and health coaches recommend making sure your diet includes grass-fed, organic meats and eggs; healthy sources of fat like cold-pressed, organic olive oil and coconut oil; and plenty of veggies, especially dark leafy greens and cruciferous vegetables, so that your fiber and antioxidant levels stay high.


What is it? The Gut and Psychology Syndrome diet, or GAPS diet, was created by Dr. Natasha Campbell-McBride, a neurologist and nutritionist.

Similar to paleo, on GAPS you eliminate grains, sugar and refined/processed carbs and focus on meats, fish, vegetables, fruits other than avocado and fermented dairy like kefir. Bone broth is also recommended with every meal.

The claim: GAPS is believed to have a positive impact on digestive diseases like Crohn’s, ulcerative colitis and IBS, allergies and arthritis, and neurologic issues like ADD/ADHD, dyslexia, depression and schizophrenia.

The truth: GAPS can be effective because, like paleo, you eliminate the grains that are triggers for inflammation, digestive issues, gut bacterial imbalances and immune dysfunction — issues that too many people suffer from today.


What is it? The Low-FODMAP diet was developed by researchers at Monash University to address gastrointestinal issues by targeting a specific category of carbohydrate called FODMAPs.

On this diet, you typically eliminate foods that contain FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) like garlic, leeks, onions, high-lactose dairy, asparagus, sugar snap peas, carrots, celery and cabbage and fruits like apples, pears, mango, nashi pears, watermelon, nectarines, peaches and plums.

The claim: This diet will reduce digestive symptoms like gas and bloating by starving the bacteria in your gut that are used to thriving on these specific carbs.

The truth: I recommend a Low-FODMAP approach as part of a protocol to address SIBO (Small Intestinal Bacterial Overgrowth), which you can test for using a specialty breath test. Both supplements and medications can help resolve this problem. Occasionally following the diet is enough, but usually resolving SIBO takes more than just cutting back with the FODMAPs diet.

Blood Type

What is it? The Blood Type Diet was popularized by the book Eat Right 4 Your Type by Dr. Peter D’Adamo, a naturopathic doctor who researched the way our blood type might make us predisposed to reacting to certain foods.

We each have a red blood cell type — A, B, O or AB. This is defined by proteins that live on the outside of our red blood cells and mark that cell as a certain type. You don’t have multiple types; all your red blood cells are one type and this is inherited.

The Blood Type Diet gets very specific, but at a high level recommends a vegetarian diet for type As, a meat-heavy diet for type Os, avoiding grains that contain proteins called lectins if you’re type B and a low-lectin, pescatarian diet for ABs.

The claim: That eating for your blood type makes it easy to lose weight, have more energy and avoid chronic diseases from autoimmune disease to heart disease to cancer, because the ABO markers are a sign of your ancestral lineage and what you might be best adapted to eat.

The truth: The rationale behind the Blood Type Diet is incredibly interesting. However, being able to explain something as a theory, and that thing actually being reliably, medically true, are two different things. There is no good, large-scale data to back up that eating for your blood type is effective.

While the Blood Type Diet may have some merit, and there is no harm generally in trying it, it is a broad simplification and most people’s genetics and current lifestyle factors are more nuanced and complicated than just their ABO blood type.

Ketogenic/High Fat

What is it? A ketogenic diet is when you strictly cut out carbs, and to a lesser extent, protein. The macronutrient that is most heavily consumed is dietary fat.

On the ketogenic diet, a typical breakfast might be an egg over a bed of leafy greens with three tablespoons olive oil, ½ avocado and ¼ cup blueberries. Lunch might be an arugula salad with almond slivers, roasted salmon, olive oil and avocado.

Many people like to consume a lot of high-fat, low-quality dairy on a ketogenic diet, but the healthiest way to approach ketosis is through a mix of avocado, coconut oil and grass-fed dairy products from sheep’s or goat’s milk.

The claim: On this diet, your body can “switch” from a carbohydrate-adapted metabolism to a fat-adapted metabolism, which can result in weight loss and better energy. This is something certain athletes strive for (think marathoners and cyclists) because it can give them lasting stamina (carbs run out quickly).

It’s also an approach to fighting cancer per certain theories of cancer development where cancer cells are believed to thrive on sugar.

In addition, the ketogenic diet is felt to be helpful in in treating some people with epilepsy and neurodegenerative diseases.

The truth: The ketogenic diet is promising for cancer, weight loss and athletic performance, but is very hard to stick to. You can get ketone urine strips from the drugstore to see if you are in a ketogenic state at the end of each day, but most people have a hard time cutting back on carbs to get there. It is also questionable whether this diet is safe long-term (there are concerns that it can lead to kidney issues). Only try a ketogenic diet under the supervision and guidance of a knowledgeable medical provider.

The AIP Diet (AutoImmune Protocol)

What is it? The AIP diet is an elimination diet that is designed to eliminate a food trigger that could be perpetuating an autoimmune disease like rheumatoid arthritis, multiple sclerosis, lupus or even Hashimoto’s thyroiditis.

There are a few versions; I typically recommend eliminating gluten/wheat, dairy, eggs, soy, corn, grains, legumes, nuts, seeds and nightshade vegetables (which are tomatoes, peppers, white potatoes and eggplant.) Instead, you focus on leafy greens, vegetables, meat/fish, herbs and certain fruits.

The claim: This diet can be very effective you have an autoimmune disease. If you see progress after three to six months, you can then reintroduce some food groups, one at a time, and see how you react. Eventually you end up, ideally, on a modified version of the diet that eliminates only what you are reacting to.

The truth: This diet can be life-saving for some people, but it isn’t for everyone! You should only embark on this diet with the supervision and the support of a knowledgeable medical provider. Most of the time, not all of the foods on the list are problematic, but getting clear on which ones are for you involves testing, and a very careful reintroduction of foods.

So what’s good for you? The number one thing you can do to be healthy — and the thing most of these diets have in common — is to remove most grains, sugar and refined carbohydrates from your diet, to eat lots of high-fiber vegetables and fruit in moderate quantities (one to two servings a day) and to get plenty of healthy fat from good sources like wild salmon, olive oil and flax seeds.

Making a major dietary change is best done in conjunction with a professional who can help you figure out what actually works for your body and help you set goals and stick to them. The hardest part isn’t usually what to eat, it’s getting the “carbage” from bars, juices, baked goods, sweets and flour out of our lives. We know eating these foods regularly isn’t good for anyone, which is hard given that we are biologically programed to like them, and they surround us at every turn.

But, if you can eliminate the carbage and stick to a diet that works for you, you’ll definitely have more energy and a lower level of inflammation in the body, which can show up as everything from depression to pain to digestive issues to breakouts.

Robin Berzin, MD is the founder and CEO of Parsley Health, a modern primary care practice in NY, LA and San Francisco that combines nutrition, prevention and wellness with cutting-edge medicine from top doctors. Dr. Berzin went to medical school at Columbia University and later trained in Internal Medicine at Mount Sinai Hospital. Illustrations by Maria Jia Ling Pitt.