The Influence of Liquid Consistency and Food Texture on Swallowing: A Systematic Review Update.
Catriona M Steele, Isuru Dharmarathna, Jacqueline K Benfield and 22 others
Thicker liquids and foods reduced penetration-aspiration in every one of 25 studies, but generally left more residue in the pharynx.
At 5 ml volumes, thick liquids showed less residue than thin sips — the trade-off is volume-dependent.
Key findings
1All 25 studies that reported swallowing-safety data for patients with dysphagia found improved safety (reduced penetration-aspiration severity or frequency) with thicker liquids or foods compared to thinner ones.
2Thicker consistencies generally produced more pharyngeal residue than thinner ones across 23 studies, but 5 ml teaspoon-sized boluses of moderately and extremely thick liquids showed less residue than sips of thinner consistencies, indicating the residue trade-off depends on bolus volume as well as thickness.
3Swallow reaction time was longer for mildly thick and thicker liquids compared to thin liquids across healthy and patient populations, and bolus volume was a prominent factor influencing upper esophageal sphincter opening duration.
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What it does not show
Meta-analysis was not possible because studies varied too much in populations, outcome definitions, bolus volumes, and scoring thresholds, so no pooled effect sizes exist — the '100% improved safety' figure is a count of studies, not a quantified effect. Many studies used different bolus volumes across consistencies (e.g., sips for thin, 5 ml teaspoons for thick), making it hard to separate a consistency effect from a volume effect. Only two of the 70 synthesized studies included children, so the evidence base for paediatric texture modification remains very thin. Several included studies labelled their stimuli with IDDSI terminology but did not report the IDDSI testing results that would confirm the label was accurate. The search cut-off was May 2024; no further update was performed. Exclusion criteria (English only, sample size ≥ 10, IDDSI terminology required, no contingent consistency assignment) may have introduced selection bias and excluded relevant work in EMG, acoustic, and accelerometry research. The review is structured entirely around the IDDSI Framework, and several authors served on the IDDSI board, which shaped the taxonomy the review uses.
Declared interests
No funding source is named. Catriona Steele was on the IDDSI board of directors from 2012 to 2023 and is a member of the Dysphagia journal editorial board. Julie Cichero was on the IDDSI board from 2012 to 2023. Carlo Pedrolli is a current IDDSI board member. The entire review is organised around the IDDSI Framework, which these authors helped create and govern.
The easy way to misread this
Do not read the '100% of studies showed improved safety' result as a blanket endorsement of thickening for every patient. The same body of evidence shows that thicker liquids generally leave more pharyngeal residue at sip volumes, and residue is a recognised risk factor for secondary aspiration. The studies also varied so much in populations, methods, and definitions that no pooled effect size exists, and the residue trade-off is volume-dependent — a 5 ml teaspoon of thick liquid may be safer and cleaner than a cup sip of thin liquid, but a large sip of thick liquid may be the worst of both worlds. The right consistency and volume are patient-specific, not a one-size-fits-all prescription.
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