Keto improved memory in older adults with cognitive impairment, but raised LDL

Cognitive impairment in later life brings substantial functional decline and a heavy care burden, and options for slowing it remain limited. Ketogenic diets, which raise ketone body levels in the blood, have been proposed as a way to support cognition in the ageing brain. Evidence in older adults who already have cognitive impairment has been inconsistent, with individual trials pointing in different directions. This review set out to pool the randomised trial evidence and answer two questions at once: whether these diets actually help cognition, and what they do to metabolic markers such as blood lipids along the way.

The authors searched seven databases, including PubMed, Embase, the Cochrane Library and several Chinese-language sources, from their inception to July 2025. They included only randomised controlled trials of ketogenic diets or related ketogenic strategies in older adults with cognitive impairment. Two reviewers independently screened studies, extracted the data and assessed each trial's risk of bias. Twelve trials met the bar, covering 707 participants in total, and the outcomes pooled included overall cognitive function, individual cognitive domains, ketone concentrations and blood lipid markers.

Compared with control interventions, ketogenic strategies improved overall cognitive function, with a standardised benefit of 0.34. Looking at specific domains, memory improved most, at 0.53, followed by language at 0.43, while attention and executive function showed no significant change. The diets clearly did what they were designed to do metabolically: acetoacetate and beta-hydroxybutyrate, the two main ketone bodies measured, both rose. The trade-off appeared in the lipid panel, where total cholesterol and LDL cholesterol increased, although triglycerides and HDL cholesterol stayed put.

Previous work on ketogenic diets and cognition in older adults was described by the authors themselves as inconsistent, so a pooled analysis showing a positive overall effect moves the field forward. The pattern is notable: benefits concentrated in memory and language rather than spreading evenly across every mental faculty. The lipid findings complicate the picture, because a diet that lifts LDL cholesterol raises its own long-term questions in an older population. Open issues include how long the cognitive gains last, whether they appear in cognitively healthy adults, and which of the various ketogenic strategies works best.

For a reader thinking about brain ageing, this is a reason to take ketogenic approaches seriously as more than a weight-loss fad: in older adults with mild cognitive impairment or Alzheimer's disease, they shifted real cognitive scores. It is equally a reason for caution, because the same diets raised total and LDL cholesterol, a cost the authors say should be considered alongside any cognitive benefit. Nothing here speaks to healthy younger brains, and the effects, while genuine, were modest rather than transformative. Anyone curious about such a diet now has both sides of that ledger in view.