What are common fillers in supplement capsules?

Why fillers exist, in one piece of arithmetic, and which ones are common

Fillers exist because a capsule is a fixed volume and a dose is a weight, and the two rarely match, which is the whole explanation and the reason a filler is not a fault. A size-00 capsule, the common large size, holds roughly 500 to 700mg of a typical powder depending on its density; a size-0 holds roughly 350 to 500mg. A product whose dose is 300mg of extract, or 750mg of magnesium bisglycinate, or 100mg of a vitamin premix, leaves space in the shell that must be filled, because a half-empty capsule rattles, doses inconsistently on the filling line, and looks as if something is missing, so a bulking agent is added to bring every capsule to the same fill weight, which is also what makes the dose per capsule consistent from the first to the last. The common fillers, in rough order of how often they appear: rice flour, usually brown rice flour, a food-grade starch that is gluten-free and hypoallergenic, the worked example's choice; microcrystalline cellulose, a purified plant fibre that is inert, non-caloric and vegan; maltodextrin, a starch-derived carbohydrate that fills well and dissolves easily; dicalcium phosphate and calcium carbonate, mineral salts used as bulking agents in tablets and some capsules; and, less often now, lactose, the milk sugar that was a traditional pharmaceutical filler. Each is a food ingredient, each is inert at the tens or hundreds of milligrams a capsule needs, and each appears in the ingredients list in the order of its weight, the filler often second after the active and before the shell.

The ones worth watching, what a no-fillers claim usually means, and the filler read as a sign of an honest label

The ones worth watching are watched for the reader's reasons rather than for any general harm. Lactose, for anyone lactose-intolerant, since a few hundred milligrams per capsule adds up over a daily dose and is declared as milk in the allergens. Maltodextrin, for the strictly carbohydrate-conscious, since it is a starch-derived sugar, though the amount in a capsule is trivial against a meal, the concern being more relevant to powders where maltodextrin can be a major ingredient. Wheat-derived starches and soya-derived ingredients, for those allergies, emphasised in the list as the law requires. And, for a vegan, the source of any stearate alongside the filler, the shell being the larger question. What a no-fillers claim usually means is one of two things: a product whose active fills the capsule on its own, a 500mg dose of a dense powder in a size-0 shell, which is fine and common for single-ingredient products with larger doses; or a marketing line on a product that uses a bulking agent under a name the reader will not recognise, or that has simply moved the filler to a smaller capsule and a higher count, three capsules where two would do, the check being the dose per capsule against the capsule size and the ingredients list read in full. The filler read as a sign: a label that names its filler, brown rice flour, and states the active's weight beside it has told the reader exactly what the capsule contains, the worked example's 750mg of bisglycinate per capsule with rice flour in the space that leaves in a size-00 shell being the honest version, and a label that hides its filler in a blend or avoids naming it having made a small thing into a question, the fillers guide's last word being that the harmless thing named is better than the harmless thing hidden.

The verdict, a filler named is a capsule explained

What are common fillers in supplement capsules: brown rice flour, microcrystalline cellulose, maltodextrin, dicalcium phosphate, calcium carbonate and, less often now, lactose, added because a capsule holds a fixed volume that a dose rarely fills and a consistent fill weight is what makes every capsule dose the same, fillers being harmless food ingredients worth watching only for lactose intolerance, strict carbohydrate counting and allergen sources, and a no-fillers claim meaning a full capsule of active or a marketing line the dose-per-capsule check settles. The filler named: Futuro Labs Magnesium Glycinate, 750mg of bisglycinate per capsule with brown rice flour in the space that leaves, an HPMC shell and nothing else, £19.99 for 90 days at 22p a day.

What to check on the label

Questions people also ask

Why do supplement capsules contain fillers?

Because a capsule is a fixed volume and a dose is a weight: a 300mg extract or 750mg of bisglycinate leaves space in a size-00 shell, and a bulking agent brings every capsule to the same fill weight so the dose is consistent and the capsule does not rattle.

Are fillers in supplements bad for you?

No: the common fillers, rice flour, microcrystalline cellulose, maltodextrin and mineral salts, are inert food ingredients at the tens or hundreds of milligrams a capsule needs, worth watching only for lactose intolerance, strict carbohydrate counting or allergens.

What is the best filler in a supplement?

Any that is named and suits the reader: brown rice flour and microcrystalline cellulose are hypoallergenic, vegan and inert, and the worked example uses brown rice flour beside its bisglycinate.

What does no fillers mean on a supplement?

Either a dose that fills its capsule on its own, common for single-ingredient products with larger doses, or a marketing line on a product using a bulking agent under an unfamiliar name or a smaller capsule and a higher count, checked by dose per capsule against capsule size.

Which fillers should lactose-intolerant people avoid?

Lactose itself, the traditional pharmaceutical filler, declared as milk in the allergens; a few hundred milligrams per capsule adds up over a daily dose, and rice flour or cellulose fillers avoid it entirely.

Sources

1. The pharmaceutical excipient literature: capsule shells, bulking agents, glidants and anti-caking agents, binders, disintegrants and coatings are functional non-active ingredients whose purpose is manufacturability, stability and dosing accuracy rather than effect. PubMed record
2. The capsule shell literature: hydroxypropyl methylcellulose capsules are plant-derived cellulose shells suitable for vegan products, gelatine shells are animal-derived, and pullulan is a fermentation-derived vegan alternative. PubMed record
3. The Food Supplements (England) Regulations 2003. https://www.legislation.gov.uk/uksi/2003/1387/contents/made
4. The retained Food Information to Consumers regulation: the mandatory nutrition declaration for foods, its fixed order of energy, fat, saturates, carbohydrate, sugars, protein and salt per 100g, and its rules on portion information, with supplements declaring nutrients per daily dose against nutrient reference values. https://www.legislation.gov.uk/eur/2011/1169/contents

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