RR. Wing, JA. Vazquez and CM. Ryan (1995). Cognitive effects of ketogenic weight-reducing diets. International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity, 19(11), 811-6.

PubMed 8589783

[Abstract]
OBJECTIVE: To determine whether ketogenic weight reducing diets have adverse effects on cognitive performance.

SUBJECTS: 21 overweight women (mean BMI = 41 kg/m2).

DESIGN: Randomized double-blinded study.

METHOD: Subjects were randomized to ketogenic or nonketogenic liquid formula very low energy diets, that were comparable in energy and in protein content. Subjects remained on the diet for 28 days and were reevaluated periodically with brief measures of cognitive performance assessing attention and mental flexibility.

RESULTS: Weight losses were comparable on the two diets (Mean = 8.1 kg). Performance on attention tasks did not differ as a function of the diet. However, performance on the trail making task, a neuropsychological test that requires higher order mental processing and flexibility, was adversely affected by the ketogenic diet. The worsening in performance was observed primarily between baseline and week one of the ketogenic diet.

CONCLUSIONS: Further research is needed to confirm this finding and to determine whether ketogenic diets negatively affect other complex mental tasks, such as problem solving.