E553aii - Magnesium trisilicate
What it is and how it is used
Magnesium trisilicate is a white, odourless powder — a magnesium silicate with a high ratio of silica to magnesium, prepared by precipitating sodium silicate with a magnesium salt. Most people meet it not as a food additive but as an over-the-counter antacid, where it has been used for decades.
In food its job is anti-caking. Its structure is highly porous, so it absorbs many times its own weight in moisture and keeps a powder free-flowing: salt that pours in a damp kitchen, spice blends that do not set solid, powdered mixes that stay loose in the packet.
Foods commonly containing it
Table salt and salt substitutes, seasoning and spice blends, powdered drink and soup mixes, and grated hard cheese.
Safety summary
Magnesium silicates are authorised in Great Britain as E 553a, with magnesium trisilicate specified as E 553a(ii).
EFSA's 2018 re-evaluation reached an unusual conclusion that is worth reporting exactly rather than smoothing over. The Panel considered the old group ADI ‘not specified’ that the Scientific Committee for Food had set in 1991 for silicon dioxide and silicates to be obsolete, finding no mechanistic rationale for a group ADI. It then concluded that on the available data the safety of these additives “cannot be assessed”.
That is a data gap rather than a finding of harm, and the Panel set out reassuring observations alongside it: absorption of silicates and talc is very low; there was no indication of genotoxicity or developmental toxicity; and no confirmed kidney effects appear in the European pharmacovigilance database despite decades of magnesium trisilicate being taken as an antacid at doses up to 4 g per person per day — far above any food additive exposure. But the honest summary is that EFSA has not been able to complete an assessment.
Known concerns
The standing concern is the assessment gap itself: EFSA declared the old group ADI obsolete in 2018 and could not complete a safety assessment on the data available. No adverse effect has been demonstrated, and antacid use at far higher doses has not produced confirmed kidney signals in pharmacovigilance data.