 Primary analysis: All the primary outcomes impairment score, inflammatory markers and cardiometabolic factors will be examined by an analysis of covariance ANCOVA including the change from baseline to completion of diet treatment as dependent variable, study group as independent variable, and baseline measures as a covariate, to evaluate the effects of a 12 week KD versus PCD. The lasting cognitive effects of a 12 week KD versus PCD six weeks post intervention completion will be examine by an ANCOVA including the change of impairment score form 12 week to 18 week as dependent variable, study group as independent variable, and impairment score at 12 week as a covariate. 