Gluten-free means a food contains less than 20 parts per million (ppm) of gluten, the threshold set by the FDA for any product carrying a “gluten-free” label in the United States. That’s less than 20 milligrams of gluten per kilogram of food. Below that level, even most people with celiac disease can eat the product without triggering a reaction.
But the term means different things in different contexts. For someone browsing the grocery aisle out of curiosity, it’s a label on a package. For someone with celiac disease, it’s a medical necessity that extends far beyond reading the front of a box.
What Gluten Actually Is
Gluten is a group of storage proteins found in certain grains. In wheat, it’s made up of two protein families in roughly equal amounts: gliadins, which dissolve in alcohol, and glutenins, which form large, stretchy polymer chains. Together, they give bread dough its elasticity and chewiness. These proteins exist only in the starchy interior of the grain kernel, where they serve as a nutrient reserve for the seed during germination.
The grains that naturally contain gluten are wheat (including all its varieties and derivatives like spelt, farro, durum, semolina, emmer, einkorn, and kamut), barley, rye, and triticale (a wheat-rye hybrid). Oats don’t inherently contain gluten, but they’re frequently processed on shared equipment with wheat, which is why many oat products carry a gluten warning unless they’re specifically certified gluten-free.
Why Some People Must Avoid It
For people with celiac disease, gluten triggers an immune attack on the lining of the small intestine. When someone with celiac eats gluten, specific peptides from the gliadin protein bind to immune molecules on the surface of certain cells, activating an inflammatory response. The immune system sends waves of immune cells, including specialized T cells, into the intestinal wall, gradually destroying the tiny finger-like projections (villi) that absorb nutrients from food.
Over time, this damage leads to a cascade of problems: diarrhea, abdominal pain, bloating, weight loss, anemia, iron deficiency, fatigue, weakened bones, and sometimes neurological symptoms like headaches or balance problems. Celiac disease is diagnosed through a combination of blood tests that detect specific antibodies and an intestinal biopsy performed during an endoscopy.
Non-celiac gluten sensitivity is a separate condition. People with this sensitivity experience many of the same digestive symptoms (diarrhea, bloating, abdominal pain, fatigue) but don’t show the antibodies or intestinal damage seen in celiac disease. They’re also less likely to develop nutrient deficiencies, weak bones, or neurological symptoms. There’s no blood test or biopsy for it. Doctors diagnose it by ruling out celiac disease first and then observing whether symptoms improve on a gluten-free diet.
What the Label Requires
Under FDA regulations, any food labeled “gluten-free,” “no gluten,” “free of gluten,” or “without gluten” must contain less than 20 ppm of gluten. The FDA chose this threshold because it’s the lowest level that can be reliably detected and measured across different types of food, from raw ingredients to baked goods. Compliance is verified using scientifically validated testing methods.
It’s worth noting that “gluten-free” doesn’t mean zero gluten. It means trace amounts so small they fall below the regulatory cutoff. For the vast majority of people with celiac disease, this level is safe. Some third-party certification programs, like those run by the Gluten-Free Certification Organization, test to even stricter standards (10 ppm), which is why you’ll sometimes see an additional certification seal alongside the FDA-compliant label.
Where Gluten Hides
The obvious sources are bread, pasta, cereal, and baked goods. The less obvious ones are scattered throughout the processed food supply. Malt, which is almost always derived from barley, appears in many products as malt flavoring, malt extract, or malt syrup. Any product containing malt is not gluten-free. Seasoning blends commonly use wheat starch, wheat flour, or malted barley flour as carrier agents. Brewer’s yeast, a byproduct of beer production, typically contains residual gluten from malt or other grains.
Caramel coloring can sometimes be made from malt syrup or wheat starch. Dextrin, a common food additive, is usually derived from corn in the United States but can come from wheat. Glucose syrup is occasionally made from wheat or barley starch. Even blue cheese is a potential concern: the mold cultures used in production may be grown on wheat, barley, or rye, and testing has found that barley-based enzymes sometimes carry enough protein to cause problems.
Cross-contact during manufacturing is another risk. Products processed on shared equipment with wheat-containing foods can pick up trace gluten even if the ingredient list looks clean. Nuts and seeds are particularly vulnerable to this, especially during sorting and packaging. Bulk bins at grocery stores present a significant cross-contact risk and are best avoided if you’re strictly gluten-free.
Gluten in Medications and Supplements
Food isn’t the only place gluten can lurk. Medications, vitamins, and supplements contain inactive ingredients called excipients, things like binders, bulking agents, and coatings. One of the most common excipients is starch, and while the vast majority comes from corn or potato, wheat-derived starch does appear in some products. A search of a National Institutes of Health medication database found over 8,300 products listing starch as an ingredient, with 11 of those specifically identifying wheat as the source.
The challenge is that no law currently requires drug manufacturers to disclose the source of their starch or other excipients on the label. If you need to verify whether a medication contains gluten, you’ll likely need to call the manufacturer directly. Outside of starch, it’s highly unlikely that any other excipient contains measurable gluten.
Nutritional Gaps to Watch For
A gluten-free diet solves one problem but can quietly create others. Many conventional wheat-based foods in the U.S. are fortified with vitamins and minerals, including iron, folic acid, and B vitamins. Their gluten-free replacements often are not. Research from the American Gastroenterological Association has found that while some nutrient levels recover after switching to a gluten-free diet (like vitamins B12 and K), others actually get worse. Folate and vitamin B6 levels tend to drop further on a gluten-free diet, and iron, zinc, copper, and vitamins A and D only partially recover.
Studies in children on gluten-free diets have found low levels of iron, calcium, folate, zinc, magnesium, and several B vitamins. This doesn’t mean a gluten-free diet is inherently unhealthy, but it does mean that people eating this way long-term benefit from periodic nutritional monitoring and may need to be deliberate about choosing nutrient-dense whole foods or fortified gluten-free products rather than relying on processed substitutes.
Gluten-Free Without a Medical Reason
Many people who eat gluten-free don’t have celiac disease or a diagnosed sensitivity. Some feel better after cutting gluten, though the reason isn’t always clear. Wheat contains other components besides gluten, including certain fermentable carbohydrates (FODMAPs), that can cause bloating and digestive discomfort in sensitive individuals. In those cases, the improvement people feel may have less to do with gluten itself and more to do with reducing overall wheat intake.
If you’re considering going gluten-free to address digestive symptoms, getting tested for celiac disease first is important. The blood tests only work while you’re still eating gluten regularly. Once you’ve removed it from your diet, the antibodies the test looks for can drop below detectable levels, making diagnosis much harder.