Diet-Induced Weight Loss Alters Functional Brain Responses during an Episodic Memory Task

Abstract

Objective: It has been suggested that overweight is negatively associated with cognitive functions. The aim of this study was to investigate whether a reduction in body weight by dietary interventions could improve episodic memory performance and alter associated functional brain responses in overweight and obese women.

Methods: 20 overweight postmenopausal women were randomized to either a modified paleolithic diet or a standard diet adhering to the Nordic Nutrition Recommendations for 6 months. We used functional magnetic resonance imaging to examine brain function during an episodic memory task as well as anthropometric and biochemical data before and after the interventions.

Results: Episodic memory performance improved significantly (p = 0.010) after the dietary interventions. Concomitantly, brain activity increased in the anterior part of the right hippocampus during memory encoding, without differences between diets. This was associated with decreased levels of plasma free fatty acids (FFA). Brain activity increased in pre-frontal cortex and superior/middle temporal gyri. The magnitude of increase correlated with waist circumference reduction. During episodic retrieval, brain activity decreased in inferior and middle frontal gyri, and increased in middle/superior temporal gyri.

Conclusions: Diet-induced weight loss, associated with decreased levels of plasma FFA, improves episodic memory linked to increased hippocampal activity.

Trial registration: ClinicalTrials.gov NCT00692536.

Fig. 1

Brain regions showing significant changes (p < 0.05; FWE-corrected for multiple comparisons) in functional brain response during memory encoding (A) and retrieval (B) after diet-induced weight loss in postmenopausal overweight and obese women (n = 20). Functional brain data is overlaid onto a rendered standardized brain in MNI space. For each cluster, the strongest peak (x y z coordinates) is plotted as bars (with standard errors) indicating % BOLD signal change in relation to mean of session pre (black bars) and post (white bars) the dietary interventions.

Fig. 2

Changes in hippocampal activity and plasma FFAs after diet-induced weight loss, R² = 0.27, p = 0.024. Note, n = 19 in this analysis due to a missing blood sample for one of the participants in the NNR diet group.