BACKGROUND AND PURPOSE: 

• Nuts appear to reduce risk of cardiovascular disease (CVD)  
• Walnuts in particular are recommended for obesity and type 2 diabetes 
  • Mechanism through which walnuts impact appetite and glycemic control is unknown 
• Farr et al. (Diabetes, Obesity and Metabolism. 2018) sought to determine whether walnut consumption impacts the neural control of appetite  

METHODS: 

• Randomized, placebo-controlled, double-blind, cross-over trial  
• 10 adult individuals with obesity (BMI ≥30 kg/m2) were included  
• Participants were randomized to 48 g of walnuts per day or an isocaloric diet without walnuts 
• Patients lived for 5 days in a controlled environment of a clinical research center, during which they were fed either walnuts or placebo using a smoothie delivery system 
• Functional Magnetic Resonance Imaging (fMRI) was used to detect parts of the brain involved 
• Visual analog scales (VAS) were used to measure subjective feelings of hunger, appetite, and fullness 
• After 5 days, participants were discharged home and placed back on a normal diet for a period of 5 weeks and then returned for a further 5 days 
• Control and exposure groups crossed over for a second series of 5 days   
• Small number of participants, but authors did power the study to answer the question  
• Primary outcome 
  • To determine how walnuts impact eating behaviors by altering neural responses to visual cues 

RESULTS: 

• 9 participants completed both 5 day series, including fMRI  
• Walnut consumption decreased feelings of hunger and appetite 
• Patients that ate walnuts had an increased activation of the right insula in response to highly desirable food cues 
• When participants received walnuts, they reported that  
  • They were less hungry compared to when they received placebo on VAS (placebo, 7.65 ± 0.99; walnut, 6.12 ± 1.16; P < .05)  
  • They could eat a smaller quantity of food while consuming walnuts (placebo, 7.55 ± 0.99; walnuts, 6.44 ± 1.01; P < .04) 

CONCLUSION: 

• Eating walnuts may increase satiety and cognitive control when faced with highly desirable foods 
• Walnuts may work by activating the right insula in the brain 
• The authors suggest that increased activation of the insula may indicate increased inhibitory control in the face of highly desirable (high-fat) food cues  
• Further studies required to determine if this response was specific to walnuts or may be generalizable to other nuts 

Learn More – Primary Sources: 

Walnut consumption increases activation of the insula to highly desirable food cues: A randomized, double-blind, placebo-controlled, cross-over fMRI study 

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