From Paleo to Blood Type, A Doctor Vets Popular Diets

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. 

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  • nevvvvave

    i’m so glad that Americans are starting to wake up to the knowledge that the main day-to-day health issues plaguing us stem from sugar and simple carb overload rather than believing fast food-funded studies that blame fat, etc for obesity and other preventable illnesses. Societies (including the US) have understood this information for generations but have been brainwashed into believing anything as long as long as money can be made as a result of sugar and salt addictions….

  • tmm16

    I recently changed my diet to try to be more paleo, but not full on.I did it mainly to cut out processed foods and help with my new exercise kick (Trying to build muscle and become more toned before bikini season!) As mentioned, I focus mainly on eating healthy, and a cheat meal here or there (like the pizza I’m treating myself to tomorrow), isn’t a big deal. Everything is about moderation 🙂

  • Sheila T.

    I did a ketogenic diet a few years ago (under the care of a dietitian) and it definitely worked (though I often felt light headed and weak), but it was really hard to adjust to life post-diet and I ended up gaining most of my weight back. Since New Year’s I’ve been focusing more on moderation, portion control, exercise, etc. and feel much better/optimistic about sustainable results. Maybe I should have adopted this lifestyle post-ketosis? But now that I am Older and Wiser, I’m realizing more and more that it’s more important to me to feel strong and healthy than anything else, even if it takes a little longer to reach my goals.

    • Cristina

      Amen sister. Shoot, once I turned 30 (well, that was just last year) but I was like EFF THIS. I gave myself a whole year to lose weight. No trendy diets, no fad diets. I was just done with diets. I’ve spent so many years dieting that I now have huge food fears and food guilt to mentally overcome. But I lost 30 lbs, I still ate pizza and queso (my life support) I just ate in moderation. And I tried to eat out less and do the portion control thing. Here I am today, still trying to overcome food fear and over eating mentally, but wayyyyy happier!

      • Sheila T.

        woohoo!! I cooked all my meals in January (part of Epicurious magazine’s Cook 90 challenge), like normal meals, and I swear I lost 7 pounds just by paying attention to what I was eating. plus I love cooking so it was a win/win!

  • Cristina

    One day, I hope “diets” aren’t even a thing anymore. I’m so over it. There’s always someone telling us something is bad. Eat all the greens but too much of one green is toxic. Too much butter and you’ll die. Don’t you dare eat that Cadbury cream egg or your brain will dissolve. Like wtf. If I want to eat Jif because it tastes way better than real peanut butter and I ENJOY, like I get physical satisfaction, when eating my toast then so be it. To me, none of these professionals address the real problem, which is over eating. This is something I struggle with even though I do eat 80/20, mostly healthy, homecooked meals. We over eat because we diet. But let’s just keep finding a new diet, not getting to the root. Ew. Our food system is f**ked.

    • Agreed. I make sure to eat plenty of fruits, veggies & other things generally accepted as healthy (although who knows these days? Maybe my quinoa is really poison), but I still love to indulge my sweet tooth. I feel healthy. I don’t get sick often and I have the energy to run around all day. I must be doing something right.

  • Jill

    I did the AIP last fall for six weeks. Not to lose weight (and it’s not meant (or even called) to be a diet, though I did lose a little weight), but to see if I really had an inlammatory trigger foods, because I have SO MUCH inflammation. It is a very rigid “protocol” but it was enlightening. As I slowly added foods back in, I realized that I don’t really have any triggers (or the ones I have, like dairy, I’ve already mostly eliminated). So I don’t really have to cut out a lot of foods…but then, I already really don’t eat much cheese / dairy, pizza, fried foods, italian, bread, or processed stuff. I’ve continued a modified version of the AIP ever since – mostly eating with a focus on more protein than I used to eat, even fewer carbs, and a lot of healthy fats (hel-lo, guacamole!!). It’s been beneficial to moderate my blood sugar which has been a key part of my feeling better and having more energy overall. To Christina’s point…I am not sure the whole / real problem is “overeating”. There’s also the quality of what we’re eating. One of the interesting side effects of the AIP was that it made me read labels more closely, and you’d be AMAZED or maybe that should be APPALLED at what’s actually “in” so much of what’s labeled “natural” or “organic” on the market. Salad dressings, ketchup, even packaged bacon…it’s not always “just” bacon…etc. Of course you can eat whatever you want. But there are consequences of what you end up putting into your body. I still like a good slice of birthday cake (the frosting!) when there’s an occasion. But commercial candy bars (which I used to love) and stuff like that? They taste horrible to me now, after having not had them for six weeks on the protocol. Regular healthy food actually tastes better (I would never have believed it if I hadn’t experienced it). And I’m really glad.

  • Bo

    I’ve said it before and I’ll say it again: I’m just going to eat the same normal, home-cooked meals that I’ve always made each night, with a glass of wine, sometimes have pizza, and patiently wait for the food marketing industry to run out of ideas.

    • gwendomouse

      My thoughts exactly.

  • SpiritAndCourage

    Everything in moderation… including moderation.

    • Amelia

      my grandmother has been saying this to me since I was a lil one!!

  • so the thesis here is to “remove most grains, sugar and refined carbohydrates”? white sugar and white flour (and alcohol) — ok that makes sense those things are nutritionally devoid — but if anyone has any insight into why whole grains are now taboo, i would appreciate! is some millet or farro or brown rice in the same league as sugar? or are some grains better than others?

    • Ana Vla

      what I’ve read is that grains don’t like to be eaten haha so they have some “protections” like molecules and enzymes in them, that cause us bloating and indigestion. BUT supposedly you can leave them all night soaking in water and that will make most of the protections go away, you then throw out the water and cook normally. I’ve been trying it but I haven’t seen any noticeable results because most of the time I forget to soak them, but I think that it can’t really hurt and it’s something relatively easy to do so why not do it?

      • jenn

        Sorry but this makes no sense. “Molecules and enzymes”? Can you be more specific? Maybe soaking overnight will soften the fibrous coatings of some grains (like steel-cut oats), but I can’t imagine what other effect it would have.

  • It’s so nice to see an actual doctor compare/contrast these different diets (I’m a medical student, and we learn about ‘nutrition’ but not much about overall diets that people are trying and how it affects their health). The Tufts nutrition newsletter (from their school of public health) is also a good resource.

    I also love that people are turning away from fear of fat. Butter, olive oil, coconut oil…make everything delicious and are much more satisfying than sugar.

    • I agree, Emily. I have Hashmoto’s and Sjogren’s and my body is doing a bang up job of attacking itself most of the time. Drugs, aside from my dessicated thyroid replacement, do not seem to work. I saw many doctors who offered me nothing but medication. I started researching diet and went on AIP, then I saw a new rheumatologist. I was afraid to tell him I was on it because I have actually been ridiculed by docs for suggesting diet. HE suggested paleo, and when I told him I was on it he congratulated me. He follows paleo himself. Board certified guy and all. On the AIP I dropped my aTPO antibodies from 1500 to 600 in about 16 weeks. I was ALWAYS at or above 1500….for the past 15 years. AIP should not be used long term. There are people who develop MAST cell/histamine issues who follow this diet. You can find recovery groups out there. I have theories of why this is. I developed severe histamine sensitivity and was down to 10 or so foods I could eat, but am recovered now. If I had more time, I would go into this as a career, but I already have another career, lol. I hope that you pursue deep understanding of nutrition and apply it to your medical practice. We need more docs like you.

      • That’s awesome. I think the difficult thing about tailoring diets to your particular state is difficult since everyone is different (and everyone has different antibodies…).

        Rheumatologists are the wizards of medicine.

  • Dyrne

    A thoughtful review of each diet. Nice change of pace from what shows up commonly on sites and blogs. Thank you.

  • Amelia

    I think I’m going to have to have someone physically reprogram my brain in order for me to ever have the self control to not eat carbs.

  • Catherine Bohner

    My biggest issue with all of these high protein, anti-grain and legume diet is how unsustainable they are from an environmental perspective. And they come off as elitist and goop-y, like only the wealthy can be healthy. I mean wild and/or sustainable seafood where I am costs $20-30/lb. So, I’ll take my grains and beans.

  • Inaat

    I should probably try to eat healthier but after years of ED, I now try to just enjoy myself and think everything in moderation. Even though I still get ideas in my head I try not acting on it and think enjoy, moderation.

  • LK

    I was religiously Paleo for 6 years and ended up with an eating disorder. I stopped listening to my body and obsessively restricted foods that I should’ve been eating in moderation (or just whenever I felt like it). I’ve learned that, for me, restriction is the true culprit.

  • gwendomouse

    That people with autoimmune- or digestive diseases need special diets sounds perfectly sensible to me. But for anyone else all of these diets seem like orthorexia. Everyone knows sugar should be enjoyed in moderation, but the degree of obsessiveness at play in some diets seems more unhealthy than the supposedly ‘bad’ foods. Are there only the two options left, either morbidly obese, sugar-addicted slob or decadent neurotic? I refuse to believe that traditional European cooking is bad for me.

  • This is so informative and a great overview. Thanks.

  • Tom Geraghty

    Low-Carb, High-Fat – did help lose weight. Then leveled off. It’s a good way to control weight so you don’t gain. There are natural sugars in most foods, and the instincts, without you knowing, are that your tastes gravitate to natural sugars to compensate for all the bread, pasta and sweets you no longer eat. However, blood sugar has come under control, pre-diabetes gone away. That part is Great. This has been a permanent change – not a temporary “diet”. About 16 months now. – lowering blood sugar (glucose) is the key to weight loss. Here’s the secret – the less sweets you eat, the less you want to eat! High sugar food are addictive!