The Metabolics Red List: The Additives and Fillers We Choose Not to Use

What goes into a supplement matters. So does what stays out. This article explains the Metabolics Red List: the additives, fillers and processing aids we choose not to use, the reasoning behind each decision, and how our approach to manufacturing makes that possible. It is written for anyone who reads the ingredient list before they buy, and for the practitioners who want to know exactly what they are recommending.

Key takeaways

•     The Metabolics Red List is a defined set of additives, fillers and processing aids that Metabolics chooses not to use in its formulations.

•     Many of these ingredients are approved and widely used across the industry. Being on the list does not mean an ingredient is unsafe. It means we do not believe it is necessary in our products.

•     The list includes magnesium stearate, titanium dioxide (E171), artificial sweeteners, colours and flavours, and a range of preservatives and processing aids.

•     Metabolics manufactures using semi-automatic equipment operated by skilled staff, which removes the need for many of the lubricants and flow agents used in high-speed production.

•     Where a carrier or processing aid arrives as part of a supplied raw material, Metabolics declares it on the label in the interests of full transparency.

What is the Metabolics Red List?

At Metabolics, we believe that what we leave out of our products is just as important as what we put in. The Metabolics Red List is the set of ingredients we choose not to use during manufacture: additives, fillers and processing aids that, in our view, do not contribute to the nutritional purpose of a product.

Our view is simple: if an ingredient does not contribute to the nutritional purpose of a product, it is reasonable to ask whether it needs to be there at all.

This does not mean that every ingredient on the list is unsafe. Many are approved for use by regulatory authorities and remain widely used within the food and supplement industry. The list reflects our formulation philosophy and our preference to avoid unnecessary additives wherever suitable alternatives exist.

Why do supplements contain fillers and additives?

Many food supplements contain ingredients that are added to improve appearance, taste, shelf life or manufacturing efficiency rather than to provide nutritional value. These can include artificial sweeteners, artificial colours, artificial flavours, preservatives, lubricants, coating agents and other processing aids, some of which serve little or no nutritional purpose.

Many of these ingredients are approved for use and widely used throughout the food supplement industry. Some, however, have been the subject of ongoing scientific investigation, emerging health concerns or consumer interest. In some cases, research has explored potential effects on areas such as gut health, glucose metabolism, endocrine function or long-term exposure. In others, concerns relate to sustainability, ingredient quality or manufacturing practices.

Why don't Metabolics supplements need these fillers?

Many supplement manufacturers use highly automated, high-speed production equipment capable of producing large volumes of capsules and tablets efficiently and cost-effectively. To keep these machines running smoothly, lubricants, flow agents, coating agents and other processing aids are often used to help powders move through machinery, prevent ingredients from sticking and improve manufacturing efficiency. There is nothing unusual about this approach, and many of these ingredients are widely used throughout the industry.

At Metabolics, we take a different approach. Our products are manufactured using semi-automatic equipment operated by skilled production staff. This allows us to produce high-quality supplements without relying on many of the lubricants, flow agents and excipients commonly used elsewhere in the industry.

This approach can be slower and more labour-intensive. In many cases, avoiding these processing aids requires additional time, care and expertise during manufacture. We believe it allows us to maintain greater control over our formulations and to minimise the use of ingredients that serve little nutritional purpose.

Which ingredients are on the Metabolics Red List?

The Red List groups into four areas: artificial sweeteners, colours and flavours; manufacturing aids and excipients; ingredient sourcing and processing methods; and preservatives and processing additives. Where a statement draws on published research or a regulatory assessment, the source is named alongside it, with full references at the end of this article.

Ingredient	What it is	Why Metabolics chooses not to use it
Artificial sweeteners, colours and flavours
Artificial sweeteners (including aspartame, acesulfame-K, saccharin and sucralose)	Synthetic sweetening agents used as sugar substitutes	Research has explored potential effects of certain artificial sweeteners on the gut microbiome, glucose regulation and taste preferences. (Suez et al., Nature, 2014)
Artificial colours	Synthetic colourings added for appearance rather than nutritional value	Some have been the subject of research and regulatory review regarding potential effects on behaviour and sensitivity reactions in certain individuals. (McCann et al., The Lancet, 2007)
Artificial flavours	Synthetic flavouring substances added primarily to modify taste	Sensitivities to flavouring ingredients can vary from person to person.
Titanium dioxide (E171)	White colouring agent formerly used in foods and supplements	In 2021, EFSA concluded that titanium dioxide could no longer be considered safe as a food additive, because concerns regarding genotoxicity could not be ruled out. (EFSA, 2021)
Manufacturing aids and excipients
Magnesium stearate	Manufacturing aid used to improve powder flow during production	Magnesium stearate is widely used throughout the supplement industry as a lubricant. The properties and use of excipients can influence the performance characteristics of a finished product, including factors such as disintegration and dissolution. (Zarmpi et al., AAPS J, 2020)
Calcium silicate, calcium stearate	Flow agent, anti-caking agent and lubricant	Used to improve manufacturing efficiency and powder flow rather than to provide nutritional value.
Talc (magnesium silicate)	Mineral-based anti-caking and flow agent	Talc is commonly used to improve powder flow and prevent clumping. Concerns have been raised historically regarding asbestos contamination in some talc deposits.
Ingredient sourcing and processing methods
Genetically modified ingredients (GMOs)	Ingredients derived from genetically modified organisms	We choose to avoid genetically modified ingredients in line with our ingredient sourcing philosophy.
Palm oil	Vegetable oil derived from oil palm fruit	We choose not to use palm oil due to environmental and sustainability considerations.
Irradiated ingredients	Ingredients treated with ionising radiation to reduce microbial contamination	Although irradiation is an approved treatment used within the food industry, Metabolics prefers to source non-irradiated ingredients.
Ethylene oxide (ETO)	Sterilising agent used on certain raw materials and botanicals	Ethylene oxide is classified as a carcinogen and its use in food ingredients is tightly regulated. (UK Health Security Agency)
Potassium bromate	Oxidising agent banned for food use in many regions	Toxicological studies have raised concerns regarding potential carcinogenicity.
Preservatives and processing additives
Sulfites (added sulfites)	Preservatives commonly used to extend shelf life	Some individuals are sensitive to sulfites, particularly those with asthma or sulfite sensitivity. For this reason, we do not intentionally add sulfites to our products. (Irwin et al., PLoS One, 2017)
Benzoates (including benzoic acid and sodium benzoate)	Preservatives used to extend shelf life	Some individuals may be sensitive to benzoates. Research has also explored potential effects on oxidative stress, inflammation and behaviour in susceptible individuals. When sodium benzoate reacts with vitamin C, it can convert to benzene, a known carcinogen. (Piper & Piper, Compr Rev Food Sci Food Saf, 2017)
Parabens	Synthetic preservatives	Some research has explored potential endocrine-disrupting properties of parabens.
Propionates	Synthetic preservatives	Emerging research has explored possible effects of propionates on metabolism and insulin regulation. (Tirosh et al., Sci Transl Med, 2019)
BHA, BHT and TBHQ	Synthetic antioxidant preservatives	Although approved for use within regulatory limits, these synthetic antioxidants have been the subject of ongoing toxicological research, including studies exploring potential effects associated with long-term exposure. (Ren et al., Foods, 2025)
Polysorbates	Synthetic emulsifiers	Research has explored potential effects of certain polysorbates on the gut barrier and gut microbiota. (Chassaing et al., Nature, 2015)
PEGs (polyethylene glycols)	Processing aids, solubilisers and coating agents	Concerns have been raised regarding potential contaminants that may arise during manufacture, including ethylene oxide and 1,4-dioxane. PEGs have also been associated with hypersensitivity reactions in susceptible individuals. (Bianchi et al., Acta Biomed, 2021)
EDTA	Synthetic preservative and chelating agent	A synthetic additive used to improve product stability by binding metal ions. While approved for use, it may also bind minerals and potentially reduce their absorption at high intakes.

The statements above are based on a combination of published scientific literature, regulatory assessments and ingredient safety reviews available at the time of writing. Scientific understanding continues to evolve, and the strength of evidence varies between ingredients. Some have been extensively studied and reviewed by regulatory authorities, while others remain the subject of ongoing scientific investigation and discussion.

What about ingredients that come from raw materials?

Transparency is an important part of the Metabolics philosophy. While we choose not to add certain ingredients directly to our formulations, some may occasionally be present as part of a supplied raw material. For example, certain botanical extracts and specialist ingredients may contain carriers or processing aids such as maltodextrin or silicon dioxide. These materials are sometimes used by ingredient manufacturers to standardise extracts, improve stability or assist with processing and handling.

In these circumstances, the ingredient is not added directly by Metabolics but is present as part of the supplied raw material. Where required, we declare these ingredients on the label in accordance with food labelling regulations and in the interests of complete transparency. Not all supplement manufacturers choose to highlight the presence of such carriers or processing aids. We believe customers and practitioners should have clear information about what is present in a product.

Banned, restricted and prohibited ingredients we also avoid

In addition to the ingredients on the Red List, Metabolics does not use botanical ingredients that are prohibited, restricted or considered unsuitable under current UK regulations and guidance. Further information can be found in the UK Government guidance: Banned and Restricted Herbal Ingredients.

Metabolics does not intentionally formulate products with substances prohibited by the World Anti-Doping Agency (WADA). However, our products are not tested for WADA-prohibited substances and are not certified for use by competitive athletes subject to anti-doping rules.

We continually monitor developments in nutritional science, food supplement legislation and ingredient safety assessments to help ensure our formulations remain aligned with current best practice. Our decisions are guided by scientific evidence, regulatory compliance, manufacturing quality and our commitment to providing products that are as clean and transparent as possible.

Frequently asked questions

Is magnesium stearate safe?

Magnesium stearate is permitted for use and is widely regarded as safe by regulatory authorities. Metabolics chooses not to use it because it functions as a manufacturing lubricant rather than as a nutrient, not because we consider it unsafe.

Why do supplements contain fillers and additives?

They are often added to improve appearance, taste, shelf life or manufacturing efficiency, or to help high-speed equipment run smoothly. Many serve little or no nutritional purpose.

Does Metabolics use artificial sweeteners, colours or flavours?

No. Artificial sweeteners, colours and flavours are on the Metabolics Red List, which means we choose not to use them in our formulations.

Are Metabolics products suitable for competitive athletes?

Metabolics does not intentionally formulate products with substances prohibited by the World Anti-Doping Agency. However, our products are not tested for WADA-prohibited substances and are not certified for use by competitive athletes subject to anti-doping rules.

Could a Red List ingredient ever appear in a product?

We do not add Red List ingredients directly. On occasion, a carrier or processing aid such as maltodextrin or silicon dioxide may be present as part of a supplied raw material. Where this is the case, we declare it on the label.

What the Red List means for you

Our aim is simple: to use ingredients because they serve a genuine nutritional or technical purpose, not because they make manufacturing easier or less expensive. For more than 35 years, Metabolics has focused on producing food supplements based on quality, scientific integrity and transparency.

References and further reading

Artificial colours

McCann D, Barrett A, Cooper A, et al. Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial. The Lancet. 2007;370(9598):1560-1567.

Artificial sweeteners

Suez J, Korem T, Zeevi D, et al. Artificial sweeteners induce glucose intolerance by altering the gut microbiota. Nature. 2014;514:181-186.

Benzoates

Piper JD, Piper PW. Benzoate and sorbate salts: a systematic review of the potential hazards of these invaluable preservatives and the expanding spectrum of clinical uses for sodium benzoate. Compr Rev Food Sci Food Saf. 2017;16(5):868-880.

BHA, BHT and TBHQ

Ren J, Li Z, Li X, et al. Exploring the mechanisms of the antioxidants BHA, BHT, and TBHQ in hepatotoxicity, nephrotoxicity, and neurotoxicity from the perspective of network toxicology. Foods. 2025;14(7):1095.

Ethylene oxide

UK Health Security Agency. Ethylene oxide: general information.

Magnesium stearate

Zarmpi P, Flanagan T, Meehan E, Mann J, Fotaki N. Impact of magnesium stearate presence and variability on drug apparent solubility based on drug physicochemical properties. AAPS J. 2020;22(4):75.

Polyethylene glycol

Bianchi A, Bottau P, Calamelli E, et al. Hypersensitivity to polyethylene glycol in adults and children: an emerging challenge. Acta Biomed. 2021;92(S7).

Propionates

Tirosh A, Calay ES, Tuncman G, et al. The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans. Sci Transl Med. 2019;11(489).

Sulfites

Irwin SV, Fisher P, Graham E, et al. Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food. PLoS One. 2017;12(10).

Synthetic emulsifiers

Chassaing B, Koren O, Goodrich JK, et al. Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome. Nature. 2015;519(7541):92-96.

Titanium dioxide (E171)

European Food Safety Authority (EFSA). Titanium dioxide (E171) no longer considered safe when used as a food additive.