Excipients in food supplements: what they're for and which ones matter

An excipient is a substance with no nutritional activity of its own. It is added to a supplement to make the form in which it is taken both possible and stable. A tablet and a capsule exist thanks to excipients, including ours: microcrystalline cellulose, for example, is present in nine of the eleven products we currently have for sale.

On the label, they are in the list of ingredients, each preceded by the function it performs. These entries are recognisable at a glance, and the substance chosen for each function reveals the criteria by which a manufacturer formulates its products. You just need to have a label in front of you.

What excipients are for in a supplement

A powder of pure active ingredient, when poured into the hopper of a tablet press or an encapsulating machine, behaves in a rather unpredictable way. It flows erratically. It cakes with the humidity in the air and adheres to the metal punches. The dosage per unit thus ceases to be consistent: one tablet may contain more active ingredient than the next.

Excipients solve physical problems of this type. They add volume to a dose that weighs a few milligrams and make the powder flow smoothly. They prevent it from absorbing water and reduce friction on the machines. They hold the tablet together and make it disintegrate at the right time. For each technical function, there are several possible substances: which one is used depends on the raw material to be processed and what one wants to achieve.

Bulking agents, disintegrants, lubricants: the technical functions declared on the label

Technical functions on the label

• Bulking agentadds volume
• Flow agenthelps the powder flow
• Anti-caking agentabsorbs moisture
• Lubricantreduces friction in machinery
• Coating agentforms the shell
• Carriercarries the powdered extract

Regulation (EU) 1169/2011 and Legislative Decree 169/2004 require that ingredients be declared in descending order of weight, and that additives be preceded by their functional category. There are six functions most often encountered on a supplement.

Bulking agent (diluent). It adds volume when the active ingredient weighs a few milligrams per dose, so that the unit is easy to handle and each tablet or capsule weighs the same. On our labels, this is microcrystalline cellulose, present in nine out of eleven of our products.

Flowing agent (glidant). It makes the powder flow smoothly inside the machines. Each unit thus receives the same dose. In our formulas, this is L-leucine.

Anti-caking agent. It prevents powders from caking and absorbs residual moisture. On our labels, this is the extract of young bamboo stems titrated in silica.

Processing lubricant. It reduces the adhesion of the powder to the metal walls of punches and dies. In the industry, this function is normally covered by magnesium stearate, which we will discuss later.

Coating agent and shell material. This is the substance that forms the wall of a capsule, or the thin coating of a tablet. It encloses the contents, protects them from air and moisture, and makes the unit easy to swallow. A vegetable capsule normally requires only a single cellulose component. A softgel, which is softer, requires more than one together: a gelling agent to hold the wall together and a humectant to keep it elastic, because the shell must remain sealed and stable. In the vegetable capsules of Bromelain 5000 GDU Gastro-resistant and Nattokinase, the material is hydroxypropyl methylcellulose (E 464) with gellan gum (E 418); in 5-HTP and in the Extra Strong Black Maca, it is hydroxypropyl methylcellulose alone. In the softgel of the Ubiquinol with Kaneka QH®, the shell is made of carrageenan as a gelling agent and glycerol as a humectant, with beeswax applied as an external coating agent.

Carrier and functional sweeteners. A carrier is the substance onto which a liquid plant extract is dried to turn it into a workable powder. In our formulas, this task is assigned to maltodextrin, a carbohydrate obtained from starch. It is widely used in many foods and supplements and is authorised as a food ingredient throughout the European Union. Functional sweeteners, on the other hand, are used to make an orodispersible tablet palatable, the kind designed to dissolve in the mouth. In the Sublingual Vitamin B12 and Sublingual Melatonin 1 mg tablets, three substances do this. Mannitol and xylitol, two polyols common in products with no added sugar, provide bulk to the tablet and allow it to dissolve. Steviol glycosides, the sweet extract of stevia, provide the sweet taste. The only warning concerns polyols, which is required by law to be stated on the label: "Contains polyols. Excessive consumption may have laxative effects."

The rule of thumb that applies to all six is: the function always precedes the name. This is how you can distinguish technical ingredients from active ones, even without knowing them. We have written a six-step guide on the entire list of ingredients, How to read a supplement label.

Magnesium stearate in supplements: what the studies really say

Magnesium stearate is the magnesium salt of stearic acid, a saturated fatty acid found in many foods. On the label, it appears as E 470b. Its function is that of a processing lubricant: it makes the powder slide on the punches and reduces machine wear. It is the most used excipient in solid forms, because it works at very low doses and with almost all raw materials.

For years, a rumour has been circulating about this substance that it "suppresses immune defences". The root of this is a 1990 study published in Immunology, in which stearic acid (the molecule, without magnesium) was brought into contact with cultured mouse lymphocytes, in vitro, to observe its effects on cell membranes [1]. The study did not involve any oral administration and did not concern human beings. The substance tested is different from the one in tablets. The leap to "magnesium stearate weakens the immune system" was made by those who cited it, never by the authors.

The current regulatory framework can be found in the 2018 EFSA re-evaluation of magnesium salts of fatty acids (E 470b), which concludes, verbatim, that these additives are "of no safety concern at the reported uses and use levels", and that a numerical acceptable daily intake is superfluous [2].

Magnesium stearate does not appear in our tablets and capsules. This is a choice made during the formulation stage: the flow function is assigned to L-leucine, an amino acid present in everyday proteins. We could have used the world's most common lubricant, as most of the industry does. We preferred a formula in which every technical item is a simple and 'clean' substance, written in full on the label. The same criterion guides the choice of anti-caking agent.

Silicon dioxide (E 551): what it is and what EFSA says

Additives in supplements: the regulatory framework

1. Reg. (EC) 1333/2008Permitted additives and conditions of use
2. Reg. (EU) 2022/63Titanium dioxide (E 171) — authorisation withdrawn
3. EFSA 2018 and 2024Opinions on E 470b and E 551

Silicon dioxide is an anti-caking agent: it absorbs moisture and prevents powders from clumping. It is authorised throughout the European Union and is very widely used, in supplements as well as in powdered foods.

From a physical point of view, EFSA describes it as synthetic amorphous silica consisting of nearly spherical nanoparticles, mostly between 2 and 28 nanometres, which aggregate with each other into complex structures [3].

The most recent opinion is from 17 October 2024 and has two halves, of which almost always only the first circulates online. The EFSA panel on additives concluded that "E 551 does not raise a safety concern in any population group", adopting a margin of exposure approach instead of an acceptable daily intake, precisely because of the limitations of the available data.

In the second half, the same document lists the remaining uncertainties. Information is lacking on the proportion of particles present in food as isolated nanoparticles rather than as aggregates. Toxicological studies conducted with a suitable dispersion protocol are scarce. And EFSA recommends lowering the limits for lead, mercury and arsenic in the additive's specifications and introducing a limit for aluminium [3].

On the research front, a 2024 study in Environmental Health Perspectives orally exposed mice to food-grade silicon dioxide for sixty days. The authors observed a reduced induction of oral tolerance to a model protein and a worsening of gluten immunopathology in mice expressing the HLA-DQ8 gene. In their conclusions, they call for human studies, which are currently lacking [4].

The point for someone reading a label is this: the body that authorises the substance states, in the same document, that it does not have specific information on it. Faced with such a situation, we have chosen another path, and for the same function, we use a substance derived from nature.

Titanium dioxide (E 171): banned in European Union supplements

For decades, titanium dioxide was the white pigment that opacified capsules and coatings. In 2021, EFSA stated that it could no longer consider it safe, due to the possible genotoxicity of its particles. With Regulation (EU) 2022/63, it lost its authorisation as a food additive, and the transition period ended on 7 August 2022. Since then, a supplement produced for the European market cannot contain it.

The absence of E 171 in a compliant European product is therefore a legal requirement.

L-leucine and bamboo silica: the ‘clean’ anti-caking agents we use

Same function, different substances

Help the powder flow

• Magnesium stearate (E 470b)
• L-leucine

Absorb moisture

• Silicon dioxide (E 551)
• Silica from bamboo extract

L-leucine is an essential amino acid, the same one found in food proteins. In powder form, it has a crystalline structure that flows well. Hence its role as a flow agent: in our tablets and capsules, it performs the task that in the industry is normally entrusted to magnesium stearate. It appears in nine of the eleven products for sale, from Vitamin C + Bioflavonoids to Potassium Citrate to Glucosamine + Chondroitin + MSM.

Bamboo extract (Bambusa bambos and Bambusa vulgaris) standardised in silica, on the other hand, takes the place that E 551 (silicon dioxide) has in other formulas: it absorbs moisture and keeps powders free-flowing. As for what ‘standardised’ means, we refer you to the guide What does standardised extract mean.

A chemical clarification. Silica is silicon dioxide, SiO₂, in both cases: saying that one is ‘organic’ and the other ‘inorganic’ is an error. The difference lies in the form and origin, and that is where the advantage of our choice lies.

E 551 is a synthetic amorphous silica, obtained industrially, which EFSA describes as consisting of aggregated nanometric particles. The silica from bamboo extract is natural silica, contained within the plant's matrix. It is obtained by water/ethanol extraction from the young stems and is brought to a guaranteed standard. The supplier's technical documentation qualifies it, pursuant to Regulation (EU) 1169/2011, as a non-engineered nanomaterial.

Supplements without excipients: what a clean formula means

A supplement without excipients does not exist: a tablet or capsule produced on an industrial scale needs some technical substance to hold its shape and to deliver the same dose in every unit. This is also true for ours, and we state it openly. Microcrystalline cellulose is an excipient and is present in nine of the eleven products we sell today. It gives the dose a workable volume, so that each tablet and each capsule weighs the same.

It makes sense, however, to talk about a clean formula. For us, it means few excipients, chosen according to a criterion we can declare and written in full on the label. The number of items matters, but which substance performs each function matters more.

Our choice, spelled out. For flow, we use L-leucine, an amino acid from dietary proteins, instead of magnesium stearate. For the anti-caking function, we use natural silica from standardised bamboo extract, instead of synthetic silicon dioxide. Faced with an uncertainty declared by the authority itself, we have preferred the 'cleanest' available alternative: this is the criterion with which all eleven of the products we sell are formulated.

How much of a tablet is taken up by excipients then depends on the chosen form: we have done the maths, numbers in hand, in Capsules or tablets: how to choose the form of a supplement.

Excipients to avoid: five questions to ask yourself when looking at a label

The last lines of the ingredients list are the ones that say the most about who formulated the product. Five questions are enough to read them.

1. Is the function written before the name? For additives, this is a legal requirement, and a label that respects this item by item is already a good sign: the person who compiles it knows what they have put inside, and writes it down.

2. How many technical terms are there, and can you recognise their function? Counting them is the quickest way to get an idea. The number also depends on the raw material, because a powder that is difficult to compress requires more. When the same function is covered by three different substances, it is worth asking why.

3. Are there synthetic colourings? In something that is swallowed, colour almost never has a technical function: on a white tablet, an azo dye is for appearance and nothing more. None appear on our eleven labels.

4. Is there an ingredient of animal origin among the auxiliaries? This is the question that matters for those who follow a vegan diet: gelatin and beeswax come from animals, and they are shown on the label. In our Ubiquinol, there is beeswax, declared with its function. The soy lecithin that appears in the same softgel is, however, a plant-based emulsifier: it is declared because the law requires everything derived from soy to be indicated, and it is a refined extract in which the protein, the one that causes the allergy, remains in trace amounts.

5. Are the mandatory warnings included? The most common is the one on polyols in orodispersible tablets, mannitol and xylitol, which the law requires to be written. Whoever includes it knows their formula inside out.

With these five questions, the comparison between two products moves to the bottom of the ingredients list, item by item.

The excipients on our labels, function by function

The table shows the functions and substances that appear on the eleven labels of the products for sale, without proportions or quantities: proportions are the topic of the article on capsules and tablets, linked above.

Magnesium stearate, silicon dioxide E 551, titanium dioxide E 171 and synthetic colourings do not appear on any of the eleven labels of the products for sale.

Frequently asked questions

What are the excipients in a supplement?

These are substances with no nutritional activity of their own, added to make the product form possible and stable. They provide bulk, make powders flow, and prevent them from absorbing moisture. They reduce friction on machinery and form the capsule shell. On the label, they are in the list of ingredients, each preceded by the function it performs.

Is magnesium stearate bad for you?

The 2018 EFSA re-evaluation of magnesium salts of fatty acids (E 470b) concludes that the additive does not raise safety concerns at the declared uses and use levels. The claim about an immunosuppressive effect comes from a 1990 in vitro study on mouse lymphocytes, using stearic acid and without any oral administration. However, for a completely "clean label" choice, the flow function in our tablets is performed by L-leucine.

What is silicon dioxide (E 551) and why is it found in supplements?

It is an anti-caking agent: it absorbs moisture and prevents powders from clumping. The 2024 EFSA opinion concludes that at the declared uses, the additive does not raise safety concerns in any population group. The same document describes the substance as consisting of aggregated nanometric particles, states the lack of data on the proportion of isolated nanoparticles as an uncertainty, and recommends lower limits for lead, mercury and arsenic. In our formulas, the anti-caking function is performed by a bamboo extract standardised in silica, in accordance with our "clean label" policy.

Is titanium dioxide (E 171) still permitted in supplements?

No. With Regulation (EU) 2022/63, it lost its authorisation as a food additive in the European Union; the transition period ended on 7 August 2022. A supplement produced for the European market after that date cannot contain it, and its absence is a legal requirement.

What is microcrystalline cellulose used for?

It is a bulking agent: it adds volume to the dose when the active ingredient weighs a few milligrams, so that each tablet or capsule is easy to handle and has the same weight. It is the most common excipient on our labels, in nine out of eleven products, and it is declared with its function before its name.

What is L-leucine in a supplement?

It is an essential amino acid used both as a supplement and as a flow agent: in the second case, it makes the powder flow smoothly inside the machines, ensuring that each unit receives the same dose. In our tablets and capsules, it performs the function that is normally covered by magnesium stearate in the industry.

Is silica from bamboo extract the same thing as silicon dioxide E 551?

Chemically, they are both silicon dioxide, and the difference lies in the form and origin: E 551 is a synthetic amorphous silica that EFSA describes as nanostructured; the silica from bamboo extract is natural silica, contained in the plant matrix, obtained by extraction from the young stems and brought to a guaranteed standard, qualified as a non-engineered nanomaterial. They are two different substances for the same function: ours follows the "clean label" policy and is a precautionary choice for the long term.

Are there supplements without excipients?

In solid form produced on an industrial scale, no, and our products are no exception: they contain microcrystalline cellulose as a bulking agent, L-leucine as a flow agent and bamboo extract standardised in silica as an anti-caking agent, all declared on the label. A clean formula is one in which there are few excipients, chosen according to a declarable criterion and declared in full.

Do excipients reduce the absorption of the active ingredient?

A correctly chosen and dosed excipient has the opposite task: to ensure that the tablet disintegrates and that the active ingredient is released as intended. The amount of active ingredient that is actually available depends on the chemical form, the product form and the time of intake, topics covered in Bioavailability of supplements: what it really depends on.

Further reading

• How to read a supplement label: a practical six-step guide
• Capsules or tablets: how the form of a supplement is chosen
• Bioavailability of supplements: what it really depends on

Regulatory references and sources

Studies and scientific opinions

1. Tebbey P.W., Buttke T.M., Molecular basis for the immunosuppressive action of stearic acid on T cells, Immunology 1990;70(3):379-84. PMID 2379942 (in vitro study on mouse lymphocytes, stearic acid).
2. EFSA ANS Panel, Re-evaluation of sodium, potassium and calcium salts of fatty acids (E 470a) and magnesium salts of fatty acids (E 470b) as food additives, EFSA Journal 2018;16(3):e05180. PMID 32625824 — doi:10.2903/j.efsa.2018.5180
3. EFSA FAF Panel, Re-evaluation of silicon dioxide (E 551) as a food additive in foods for infants below 16 weeks of age and follow-up of its re-evaluation as a food additive for uses in foods for all population groups, EFSA Journal 2024;22(10):e8880. PMID 39421729 — doi:10.2903/j.efsa.2024.8880
4. Lamas B. et al., Evaluating the Effects of Chronic Oral Exposure to the Food Additive Silicon Dioxide on Oral Tolerance Induction and Food Sensitivities in Mice, Environ Health Perspect 2024;132(2):27007. PMID 38380914 — doi:10.1289/EHP12758 (study in mice).

Legal references

1. Regulation (EC) No 1333/2008 — authorised food additives and conditions of use.
2. Regulation (EU) No 1169/2011 — food information to consumers: list of ingredients and functional classes of additives.
3. Regulation (EU) 2022/63 — withdrawal of the authorisation of titanium dioxide (E 171) as a food additive.
4. Legislative Decree of 21 May 2004, No 169 — implementation of Directive 2002/46/EC on food supplements.