We conducted a systematic review and meta-analysis investigating the influence of acetylcholinesterase inhibitors (AChEIs) therapy on nutritional status and weight across observational and interventional studies. Two authors searched major electronic databases from inception until 10/14/2015 for longitudinal, open-label and randomised double-blind placebo controlled (randomised controlled trials (RCTs)) studies of AChEIs in patients with dementia reporting nutritional status outcome data. Out of 3551 initial hits, 25 studies (12 open-label trials, 9 RCTs and 4 longitudinal studies) including 10 792 patients with dementia were meta-analysed. In longitudinal studies (median follow-up 6 months), a significant cumulative incidence of weight loss between baseline and follow-up evaluation was observed (studies=2; 5%; 95% CI 1% to 34%, p<0.0001; I2 =95%). These findings were confirmed in open-label trials (6%; 95% CI 4% to 7%, p<0.0001; I2 =78%). In 9 RCTs (median follow-up 5 months), those taking AChEIs more frequently experienced weight loss than participants taking placebo (OR=2.18; 95% CI 1.50 to 3.17, p<0.0001; I2 =29%). AChEIs therapy contributes to weight loss in patients with dementia, with a 2-fold increased risk observed in the meta-analysis of RCTs. Clinicians should carefully consider the benefit and risk of prescribing AChEIs. Nutritional status should be routinely evaluated in patients with dementia treated with AChEIs. © 2016 Published by the BMJ Publishing Group Limited.