Background and Objective: As ageing of the population accelerates, cognitive impairment, in the form of conditions such as Alzheimers disease (AD) and mild cognitive impairment (MCI), is an important public health issue that has drawn a lot of attention. Nutritional intervention is a promising non-pharmacological therapy for cognitive dysfunction, but it is unclear which type of nutritional intervention is the best. This study involved a systematic review and network meta-analysis (NMA) to inform clinical practice by comparing different nutritional interventions. Methods: A pair-wise and network meta-analysis were adopted to analyse the intervention effectiveness according to direct and indirect evidence. In this study, 11 comparative nutritional interventions, which were: multi-ingredient (such as omega-3 fatty acid with antioxidant) nutrition, omega-3 fatty acid, vitamin B complex, vitamin E complex, Vitamin D, minerals, chemical compounds, dietary interventions, triglycerides, coenzyme Q, Chinese herbs, and a placebo group, were included. The mini mental state examination (MMSE) was the primary outcome and the cognitive subscale of the AD assessment scale (ADAS-cog) was the secondary outcome. Results: Fifty-one trials were included, in which 8,420 people took part in the study. For the primary outcome, 39 trials were eligible, which involved 6,698 participants. Our NMA analysis indicated that multi-ingredient nutrition (standardised mean difference (SMD) = 1.30; 95% confidence interval (CI) = 0.43, 2.30) was statistically superior to placebo, and this finding was confirmed through the application of pair-wise meta-analysis (SMD = 0.45, 95%CI = 0.14, 0.77). The subgroup analysis indicated that multi-ingredient nutrition (SMD = 1.30, 95%CI = 0.64, 2.0) was superior to placebo as measured by MMSE in the MCI group. In the AD group, no potentially promising intervention was identified. Conclusions: Our study concluded that multi-ingredient supplementation might be the most effective nutritional intervention to prevent cognitive decline among patients with cognitive impairment, especially those with MCI.