Most people read a supplement label until the box ends. The small print underneath, usually titled "Other ingredients," gets a quick glance at best. On some products, though, it's the longest list on the bottle.
If your gut is sensitive, that list deserves a closer look. These are the questions that come up most often.
What counts as an "other ingredient"?
Everything that isn't the active ingredient. That includes:
Capsule shells, such as gelatin or hypromellose, a plant-based cellulose.
Fillers, such as microcrystalline cellulose or rice flour, which bring a small dose up to a capsule-sized amount.
Flow agents, such as magnesium stearate or silicon dioxide, which keep powders from clumping and sticking to machines.
Coatings, sweeteners, flavors and colors, especially in tablets, gummies and chewables.
Like a food ingredient list, these are listed in order of weight, from most to least. Capsule type mostly matters for dietary and religious preferences: gelatin comes from animal collagen, while vegetarian capsules are usually hypromellose or pullulan.
Are "inactive" ingredients really inactive?
They're there for manufacturing, not for your health. But "inactive" doesn't mean nothing can happen. When researchers analyzed the inactive ingredients in approved oral medications, they found that a majority of medications contained ingredients that could cause adverse reactions in some people (Reker et al., 2019). That analysis looked at medicines, not supplements, but supplements rely on many of the same helper ingredients.
A long chemical-sounding name tells you nothing about safety on its own. What matters is whether an ingredient is one your body is known to react to.
I'm lactose intolerant. Should lactose in a capsule worry me?
Probably not much. Lactose is sometimes used as a filler, but a capsule weighs well under a gram in total. For perspective, in a double-blind trial of 30 people who described themselves as severely lactose intolerant, drinking 240 ml (8 oz) of milk daily with breakfast for a week caused minimal symptoms, no different from lactose-free milk. The researchers concluded that symptoms are likely to be negligible when lactose is limited to about a cup of milk a day (Suarez et al., 1995).
If you react strongly anyway, or you take several products that list lactose, choosing lactose-free versions is an easy fix.
Why do gummies and gut products contain sugar alcohols or inulin?
Names like sorbitol, maltitol, xylitol, isomalt and erythritol sweeten without adding much sugar. The catch is that polyols, the scientific name for sugar alcohols, are poorly absorbed. A systematic review found they can cause dose-dependent gas, abdominal discomfort and laxative effects in healthy people and in people with IBS, and that malabsorption increases when different polyols are eaten together (Lenhart and Chey, 2017).
A single gummy is unlikely to matter much. Three gummy supplements a day, sugar-free gum and a low-sugar protein bar is a different story.
Inulin, chicory root, FOS and oligofructose sometimes appear in the other ingredients line of probiotics and gummies. They ferment quickly and are a common reason a "gut health" product leaves you more bloated. Here's the full explanation.
Is titanium dioxide something to avoid?
Titanium dioxide is a color that makes tablets and coatings bright white. In 2021, the European Food Safety Authority concluded that it can no longer be considered safe as a food additive, mainly because a concern about damage to genetic material couldn't be ruled out (EFSA FAF Panel, 2021). The European Union has since stopped allowing it in food, while it's still permitted in the US. Many brands now skip it, so it's easy to avoid if you'd rather.
A quick scan for sensitive guts
Look for sugar alcohols, especially in gummies, chewables and powders.
Look for inulin, chicory root, FOS or an unspecified "prebiotic blend."
Note lactose if you're very sensitive or take several products that contain it.
Check for colors or sweeteners you'd rather avoid.
Count how many products you take. Small amounts add up across a day.
If your digestion changed after switching brands, put the old and new labels side by side. Sometimes the active ingredient is identical, and the difference is a sweetener, a filler or an added fiber in the small print.
When to get help
Hives, swelling of the lips or face, or trouble breathing after a new supplement need urgent care. Persistent diarrhea, blood in your stool or unexplained weight loss need a doctor's visit, whatever you suspect the cause to be.
Sources
Reker D, Blum SM, Steiger C, et al. "Inactive" ingredients in oral medications. Sci Transl Med. 2019;11(483):eaau6753. PMID 30867323
Suarez FL, Savaiano DA, Levitt MD. A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance. N Engl J Med. 1995;333(1):1-4. PMID 7776987
Lenhart A, Chey WD. A systematic review of the effects of polyols on gastrointestinal health and irritable bowel syndrome. Adv Nutr. 2017;8(4):587-596. PMID 28710145
EFSA Panel on Food Additives and Flavourings (FAF), Younes M, Aquilina G, Castle L, et al. Safety assessment of titanium dioxide (E171) as a food additive. EFSA J. 2021;19(5):e06585. PMID 33976718
This article is for general information and isn't medical advice. If you have a food allergy, celiac disease or a digestive condition, check with your healthcare provider or pharmacist about specific products.
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