Gluten-Free Diet 101: A Complete Scientific Guide

by OneGoodFoodBlog
Gluten-Free Diet 101: A Complete Scientific Guide

Many diets become popular thanks to celebrity endorsements — think Kanye West on paleo, or Jennifer Aniston doing intermittent fasting — or because of commercial success, as with WW and the South Beach Diet. But others, like the gluten-free diet, have arisen from a legitimate medical need.

A diet without gluten is used to help alleviate symptoms of celiac disease, an autoimmune condition that affects nutrient absorption and prevents the digestion of gluten. Now many people are going gluten free despite not having this or other similar health conditions that necessitate eliminating gluten. People who follow a gluten-free diet for a nonmedical reasons may be seeking weight loss, better focus, increased energy, or a less-bloated belly, all benefits touted by wellness influencers.

There’s no question that the gluten-free diet has become popular for nonmedical reasons. In fact, the number of people on the gluten-free diet is almost double the number of people diagnosed with celiac disease. According to a study published November 2016 in the journal JAMA Internal Medicine, 2.7 million people in the United States follow a gluten-free diet without having celiac. The demand for gluten-free foods in the United States is also significant, with sales of gluten-free products totaling more than $15.5 billion in 2016, notes a study published February 2018 in the journal Gastroenterology & Hepatology.

If you don’t have a medical need to eliminate gluten, is this diet beneficial for you?

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First things first: Gluten is a protein. Mary Ellen Phipps, MPH, RDN, owner of Milk & Honey Nutrition in Houston, says gluten is found in wheat (including spelt, kamut, farro, durum, bulgur, and semolina), barley, rye, and triticale.

Oats are naturally gluten free, but may also be cross-contaminated with gluten if they were processed in a facility with gluten-containing foods.

Most beers, certain condiments, and other processed foods may also contain gluten by-products.

While whole grains are healthy, they can cause harmful symptoms, including bloating and fatigue, in some people. In those with celiac disease, they can lead to more severe issues, like malnutrition and intestinal damage, according to the Harvard T.H. Chan School of Public Health.

Medically speaking, not all gluten-related issues are created equal. There can be confusion around two common gluten-related conditions in particular: celiac disease and nonceliac gluten sensitivity.

Let’s take a look at the differences between the two, and how the gluten-free diet may benefit both, along with some other medical conditions.

Celiac Disease

Celiac disease is an autoimmune disorder that affects about 1 in every 141 people in the United States, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). It’s likely that even more people have the condition, because it is known to be underdiagnosed, as an article in American Family Physician points out.

In people with celiac disease, ingesting gluten causes damage to the lining of the small intestine, which can cause long-term problems with digestion and other unpleasant symptoms.

“If people with celiac consume gluten, the immune system is triggered to attack the small intestine, causing inflammation, damage, and the prevention of nutrients from being absorbed,” says Rachel Begun, RDN, of Los Angeles, a former national media spokesperson for the Academy of Nutrition and Dietetics.

Symptoms of celiac disease vary from person to person, but per the Mayo Clinic, they can include diarrhea, constipation, gas, nausea, and abdominal pain, as well as symptoms outside the digestive system, such as osteoporosis, anemia, headaches, and joint pain. Other people may not have any outward symptoms at all, but are still at risk for long-term health issues, according to the Celiac Disease Foundation.

Whether or not you have symptoms, the best way to find out if you have celiac disease is through a blood test, a biopsy, or sometimes both, according to a study published in United European Gastroenterology Journal in June 2019. The study also notes that the primary treatment for celiac disease is a gluten-free diet.

Non-Celiac Gluten Sensitivity

Non-celiac gluten sensitivity (NCGS) can be difficult to diagnose because it mimics symptoms of many other digestive disorders, and because most symptoms in scientific studies are self-reported by participants, notes an October 2018 review article published in the journal F1000Research.

“If a doctor rules out celiac and conditions with similar symptoms, such as Crohn’s disease or IBS, but your symptoms improve after banning gluten, that may indicate a gluten sensitivity,” says Begun.

Symptoms of NCGS vary from person to person, but may include brain fog, depression, bloating, abdominal pain, diarrhea, fatigue, joint pain, and other indications, according to the Celiac Disease Foundation.

Diagnosing NCGS remains tricky because of the reliance on self-reported data and the lack of ways to clinically test for it, as the aforementioned study notes, but one indicator of NCGS includes having symptoms but testing negative for celiac disease.

Gluten Ataxia

Gluten ataxia falls under the spectrum of gluten-related conditions, and affects the brain rather than the digestive system. According to a past study, in some people, gluten triggers an autoimmune attack on the cerebellum — the area of the brain responsible for functions like balance and coordination, which can cause ataxia.

Symptoms of ataxia vary, but may include difficulty using arms and legs, trouble speaking, and poor coordination and balance, notes the patient advocacy organization Beyond Celiac.

Gluten ataxia usually shows up around age 50, and many patients will have neurological symptoms but no digestive symptoms, notes a study published in February 2019 in the journal Nutrients.

Wheat Allergy

Sometimes mistaken for celiac disease, a wheat allergy is triggered by food containing wheat. The Mayo Clinic notes that it’s several proteins in wheat that cause this type of reaction, whereas people with celiac disease react only to gluten (one specific protein in wheat).

Wheat allergies are most common in children, and more than 60 percent of people affected will outgrow the allergy while they’re still relatively young, according to the American College of Allergy, Asthma, and Immunology (ACAAI). Symptoms can include a rash, hives, stomachache, runny nose, and anaphylaxis, and, per the ACAAI, the primary treatment is to avoid foods and products containing wheat, which can but doesn’t always include foods with gluten. For example, as the Whole Grains Council notes, rye and barley contain gluten but are not wheat, so those with a wheat allergy may be able to eat these grains as long as they haven’t been cross-contaminated with wheat. Be sure to read ingredient labels carefully to avoid wheat.

In addition to celiac, NCGS, gluten ataxia, and wheat allergy, according to the aforementioned Gastroenterology & Hepatology study, a gluten-free diet may play a role in treating:

Eliminating gluten may improve athletic performance in some individuals, too, per the aforementioned study. Yet the diet isn’t recommended for every athlete, so don’t follow it before getting your doctor’s approval.

There’s no shortage of claims about the gluten-free diet, but sometimes not eating gluten for a nonmedical reason can have unintended consequences. “Going on a gluten-free diet when you don’t need to can actually cause more harm than good,” says Begun.

One unwelcome side effect of a gluten-free diet is an increased risk for nutrient deficiencies, including vitamin D, vitamin B12, and folate, according to a review published in December 2016 in Clinical Nutrition. The authors also noted that fiber, iron, magnesium, zinc, and calcium are possible deficiencies that may result from unnecessarily eliminating gluten from your diet.

According to the aforementioned Gastroenterology & Hepatology paper, excess fat in the blood and coronary artery disease are additional risks of the gluten-free diet. And, while not a health risk, gluten-free products can be expensive.

Phipps adds that your body can have trouble readjusting if you swear off gluten and suddenly reintroduce it back into your diet.

If you’ve gone gluten-free and fit into one of the following categories, you may want to consider welcoming the protein back into your diet.

People Without Allergies or Intolerances

If your body doesn’t react negatively to gluten, Phipps says it’s simply not necessary to avoid it. “There’s no need to swear off any one food to gain better health or promote weight loss when it’s not medically necessary,” she says.

For optimal health and weight, Phipps says it’s about finding and maintaining the right balance of food groups, choosing quality foods, and figuring out what works best for your lifestyle.

People Looking to Lose Weight

“Don’t mistake the hype around the gluten-free diet as proof that it’s an effective or safe weight loss tool,” says Phipps. “There is no scientific evidence that avoiding gluten will lead to weight loss.”

Some people who go on a gluten-free diet will lose weight, but usually that’s because they’re cutting out foods like cookies, cake, and pasta — foods containing gluten that are also high in calories. Because there are so many processed gluten-free foods packed with fat and sugar, you may even gain weight on a gluten-free diet, according to the Gluten Intolerance Group of North America.

People on Low-Carb Diets

“The most common misconception around gluten-free diets is that they are synonymous with carb-free diets,” says Phipps. That’s simply not true.

Bananas, for example, are naturally gluten free but still contain carbs. For example, a medium-size banana contains 27 grams (g) of carbs, according to the U.S. Department of Agriculture. Per the Mayo Clinic, a standard low-carb diet limits carbs to between 20 to 60 g of carbs daily.

Most vegetables and dairy products are also naturally gluten free, and still contain carbs. Gluten-free products eliminate grains such as wheat, rye, and barley, but their gluten-free counterparts — gluten-free rice, quinoa, and corn — may have just as many carbs, notes the study. So if you’re trying to scale back your carb intake, going gluten free won’t necessarily accomplish that goal.

The bottom line: Don’t self-diagnose a gluten intolerance of any sort. Because of the potential risks, going gluten-free isn’t a good choice without a medical diagnosis, and you’re best off speaking with a doctor if you’re experiencing symptoms, notes a review article published in March 2019 in the Journal of Nutrition and Metabolism.

If you and your healthcare provider have determined that going gluten-free is right for you, the first steps include reading food labels carefully, getting rid of gluten-containing products, and restocking your pantry and fridge with gluten-free options. Working with a registered dietitian who is knowledgeable about celiac disease and a gluten-free diet can help make the transition to this eating style easier. Know that for people with celiac disease, no amount of gluten is safe to consume. You can’t go on and off a gluten-free diet or have a cheat day. Even without symptoms, gluten will damage the villi in the intestines of those with celiac, research has shown.

“There is a big learning curve to looking for gluten-free alternatives, and it takes considerable time and experience,” says Begun.

Check for the “Certified Gluten-Free” seal on food packages, and read the ingredient list on food labels. Foods regulated by the U.S. Food and Drug Administration (FDA) may be gluten-free but aren’t required to be labeled as such. Several foods, such as rice, are naturally gluten free, per Beyond Celiac, so knowing those foods is important, too.

Other tips from the Celiac Disease Foundation on how to tell if packaged food is free of gluten include checking a list of allergens, identifying any obvious sources of gluten (wheat, barley, rye), and looking into hidden ingredients or those you haven’t heard of before.

With your healthcare team’s okay, follow this list of foods with and without gluten to address your health concern.

What to Avoid

Gluten-containing grains:

  • Wheat
  • Barley
  • Bulgur
  • Cross-contaminated oats (check the label to ensure the food is gluten-free)
  • Rye
  • Seitan

Pure wheat and all its forms. This includes, but is not limited to:

  • Wheat starch
  • Wheat bran
  • Wheat germ
  • Couscous
  • Cracked wheat
  • Farro
  • Semolina
  • Spelt


  • Most beer (unless clearly marked gluten free)
  • Malt beverages

Other unexpected items:

  • Barley malt
  • Some chicken, beef, and vegetable broths
  • Malt vinegar
  • Some salad dressings
  • Veggie burgers
  • Frozen meals
  • Condiments
  • Soba noodles

Naturally gluten-free foods:

  • Fruits
  • Vegetables
  • Meat
  • Poultry
  • Seafood
  • Dairy
  • Beans
  • Legumes
  • Nuts

Naturally gluten-free grains, seeds, and starches:


  • Water
  • Sparkling water
  • Soda
  • Juice
  • Sports drinks
  • Wine
  • Hard liquor
  • Gluten-free beer

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