The quick answer is that it can be either, but it all depends on the individual.
Gluten is most often associated with wheat and wheat-containing foods that are abundant in our food supply. Negative media attention on wheat and gluten has caused some people to doubt its place in a healthful diet. There is little published research to support these claims; in fact published research suggests the opposite.
In a 2017 study of over 100,000 participants without celiac disease, researchers found no association between long-term dietary gluten consumption and heart disease risk.  In fact, the findings also suggested that non-celiac individuals who avoid gluten may increase their risk of heart disease, due to the potential for reduced consumption of whole grains.
- Many studies have linked whole grain consumption with improved health outcomes. For example, groups with the highest intakes of whole grains including wheat (2-3 servings daily) compared with groups eating the lowest amounts (less than 2 servings daily) were found to have significantly lower rates of heart disease and stroke, development of type 2 diabetes, and deaths from all causes. [2-5]
Gluten may also act as a prebiotic, feeding the “good” bacteria in our bodies. Arabinoxylan oligosaccharide is a prebiotic carbohydrate derived from wheat bran that has been shown to stimulate the activity of bifidobacteria in the colon. These bacteria are normally found in a healthy human gut. Changes in their amount or activity have been associated with gastrointestinal diseases including inflammatory bowel disease, colorectal cancer, and irritable bowel syndrome. [6,7]
When Gluten Is a Problem
What’s not great about gluten is that it can cause serious side effects in certain individuals. Some people react differently to gluten, where the body senses it as a toxin, causing one’s immune cells to overreact and attack it. If an unknowingly sensitive person continues to eat gluten, this creates a kind of battle ground resulting in inflammation. The side effects can range from mild (fatigue, bloating, alternating constipation and diarrhea) to severe (unintentional weight loss, malnutrition, intestinal damage) as seen in the autoimmune disorder celiac disease. Estimates suggest that 1 in 133 Americans has celiac disease, or about 1% of the population, but about 83% of them are undiagnosed or misdiagnosed with other conditions. [8,9] Research shows that people with celiac disease also have a slightly higher risk of osteoporosis and anemia (due to malabsorption of calcium and iron, respectively); infertility; nerve disorders; and in rare cases cancer.  The good news is that removing gluten from the diet may reverse the damage. A gluten-free diet is the primary medical treatment for celiac disease. However, understanding and following a strict gluten-free diet can be challenging, possibly requiring the guidance of a registered dietitian to learn which foods contain gluten and to ensure that adequate nutrients are obtained from gluten-free alternatives. Other conditions that may require the reduction or elimination of gluten in the diet include:
- Non-celiac gluten sensitivity, also referred to as gluten sensitive enteropathy (GSE) or gluten intolerance—An intolerance to gluten with similar symptoms as seen with celiac disease, but without the accompanying elevated levels of antibodies and intestinal damage. There is not a diagnostic test for GSE but is determined by persistent symptoms and a negative diagnostic celiac test.
- Wheat allergy—An allergy to one or more of the proteins (albumin, gluten, gliadin, globulin) found in wheat, diagnosed with positive immunoglobulin E blood tests and a food challenge. Compare this with celiac disease, which is a single intolerance to gluten. Symptoms range from mild to severe and may include swelling or itching of the mouth or throat, hives, itchy eyes, shortness of breath, nausea, diarrhea, cramps, and anaphylaxis. People who test negative for this condition may still have gluten sensitivity. This condition is most often seen in children, which most outgrow by adulthood.
- Dermatitis herpetiformis (DH)—A skin rash that results from eating gluten. It is an autoimmune response that exhibits itself as a persistent red itchy skin rash that may produce blisters and bumps. Although people with celiac disease may have DH, the reverse is not always true. Those with DH often do not have any digestive symptoms.
It is important to note that gluten is a problem only for those who react negatively to it. Most people can and have eaten gluten most of their lives, without any adverse side effects.
What is Gluten?
Gluten is a protein naturally found in some grains including wheat, barley, rye, and spelt. It acts like a binder, holding food together and adding a “stretchy” quality—think of a pizza maker tossing and stretching out a ball of dough. Without gluten, the dough would rip easily.
Other grains that contain gluten are wheat berries, durum, emmer, semolina, farina, farro, graham, khorasan wheat, einkorn, and triticale (a blend of wheat and rye). Oats—though naturally gluten free—often contain gluten from cross-contamination, as they are processed in the same facilities as the grains listed above. Gluten is also sold as wheat gluten, or seitan, a popular vegan high-protein food. Less obvious sources of gluten include monosodium glutamate (MSG), soy sauce, lecithin, modified food starch, and occasionally medications and vitamins (from cross-contamination or the use of wheat starch as fillers or in the coatings).
What Is a “Gluten-Free Diet”?
This is essentially a diet that removes all foods containing or contaminated with gluten. However, since gluten-containing whole grains contain fiber and nutrients including B vitamins, magnesium, and iron, it’s important to make up for these missing nutrients. Along with consuming naturally gluten-free foods in their whole form like fruits, vegetables, legumes, nuts, seeds, fish, eggs, and poultry, the following whole grains are also inherently gluten-free:
- Brown, black, or red rice
- Oats (when not contaminated during growing/processing)
It’s also key not to rely on processed gluten-free foods that may be high in calories, sugar, saturated fat, and sodium and low in nutrients, such as gluten-free cookies, chips, and other snack foods. Often, these foods are made with processed unfortified rice, tapioca, corn, or potato flours.
The gluten-free food industry has grown 136% from 2013 to 2015 with almost $12 billion in sales in 2015. Interestingly, studies show that people who do not have celiac disease are the biggest purchasers of gluten-free products.  Consumer surveys show that the top three reasons people select gluten-free foods are for “no reason,” because they are a “healthier option,” and for “digestive health.”  For those who are not gluten-intolerant, there is no data to show a specific benefit in following a gluten-free diet, particularly if processed gluten-free products become the mainstay of the diet. In fact, research following patients with celiac disease who change to a gluten-free diet shows an increased risk of obesity and metabolic syndrome. This could be partly due to improved intestinal absorption, but speculation has also focused on the low nutritional quality of processed gluten-free foods that may contain refined sugars and saturated fats and have a higher glycemic index. [13,14]