Effect of low-carbohydrate diets on quality of life, mental health, and speed of memory in adults: a systematic review and meta-analysis of randomised controlled trials

Low-carbohydrate diets (LCD) have inconclusive impacts on psychological outcomes, quality of life (QoL), and cognition. This study summarised current evidence by searching PubMed/Medline, Scopus, and Web of Sciences until October 2024. Thirty randomised controlled trials (RCTs) were included with a total sample size of 1781 (923 in the LCD group and 853 in the control group). No significant effect of LCD on mood disturbance, depression, anxiety, QoL, or memory speed was found. Subgroup analysis, however, showed significant QoL improvement in subjects consuming ≥15% of energy from carbohydrate, and trials with follow-up over 120 days. Of note, LCD significantly increased QoL in patients with neurological disorders. However, an unfavourable decrease in memory speed was observed in adults older than 55 years, and those consuming ≥15% of energy from carbohydrate. Findings demonstrated contradictory effects of LCD on QoL, mood, mental health, and memory speed.