Abstract: No trials on modification of food met the inclusion criteria. We included two studies that examined modification to fluids. Both were part of the same large multicentre trial and included people with dementia and people with or without dementia and Parkinson's disease. Participation in the second trial was determined by results from the first trial. With unpublished data supplied by study authors, we examined data from participants with dementia only. The first study, a cross-over trial, investigated the immediate effects on aspiration of two viscosities of liquids (nectar thick and honey thick) compared to regular liquids in 351 participants with dementia using videofluoroscopy. Regular liquids with a chin down head posture, as well as regular liquids without any intervention were also compared. The sequence of interventions during videofluoroscopy may have influenced response to intervention. The second study, a parallel designed RCT, compared the effect of nectar and honey thick liquids with a chin down head posture over a three-month period in a subgroup of 260 participants with dementia. Outcomes were pneumonia and adverse intervention effects. Honey thick liquids, which are more consistent with descriptors for 'spoon thick' or 'extremely thick' liquids, showed a more positive impact on immediate elimination of aspiration during videofluoroscopy, but this consistency showed more adverse effects in the second follow-up study. During the second three-month follow-up trial, there were a greater number of incidents of pneumonia in participants receiving honey thick liquids than those receiving nectar thick liquids or taking regular liquids with a chin down posture. There were no deaths classified as 'definitely related' to the type of fluids prescribed. Neither trial addressed quality of life. Risk of bias for both studies is high. The overall quality of evidence for outcomes in this review is low. We are uncertain about the immediate and long-term effects of modifying the consistency of fluid for swallowing difficulties in dementia as too few studies have been completed. There may be differences in outcomes depending on the grade of thickness of fluids and the sequence of interventions trialled in videofluoroscopy for people with dementia. Clinicians should be aware that while thickening fluids may have an immediate positive effect on swallowing, the long-term impact of thickened fluids on the health of the person with dementia should be considered. Further high-quality clinical trials are required.

Plain-language summary: We found two studies, which were both part of the same multicentre trial and included people with dementia and people with or without dementia and Parkinson's disease. We included data on people with dementia only. The first of the two studies looked at the immediate effects of two viscosities of liquids compared to regular thin liquids on aspiration (entry of food or fluid into the lungs) in 351 people with dementia. This study also compared drinking regular thin liquids using a chin down head posture as well as drinking regular thin liquids without any changes to head position; the main outcome was fluid entering the lungs. Using a subgroup of 260 people with dementia from the first study, the second study compared the effect of the same liquid viscosities with a chin down head posture. The effectiveness of these interventions on the incidence of pneumonia and adverse effects of these interventions was examined over a three-month period. Honey thick viscosity liquids, which clinically are similar to descriptions of 'very thick liquids', had a more positive immediate impact on preventing fluid entering the lungs when examined during videofluoroscopy (specialised swallow x-ray) examination. However, during the three-month follow-up period there were a greater number of incidents of pneumonia in the group of people with dementia receiving these honey thick liquids, than those receiving nectar thick liquids and those receiving regular thin liquids with a chin down posture. There were no deaths classified as 'definitely related' to the type of liquids that the person with dementia was receiving. There were a number of methodological flaws in both studies in this review and these were acknowledged by the authors. While thickening fluids may have an immediate positive effect on swallow function, clinicians should consider the effects of this intervention on the person with dementia in the longer-term. People with dementia on thickened fluids require long-term follow-up. The overall risk of bias of included studies is high. The quality of evidence is low. Further well-designed research is needed.