Cognitive effects of ketogenic weight-reducing diets.

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.