Obesity is a metabolic and inflammatory disorder that represents a major risk factor for development of comorbidities such as cardiovascular diseases or diabetes. Obese patients also often experience mood and cognitive dysfunctions, which drastically worsen obesity. Reducing their development may therefore allow improving health and quality of life of obese patients. Converging studies suggested that inflammation, which is a key component of severe obesity, might contribute to development of neuropsychiatric alterations, especially when it occurs in brain areas controlling mood and cognition such as the hippocampus. Nutrients such as n-3 polyunsaturated fatty acids (n-3 PUFAs) or antioxidants (AO) are known to improve emotional and cognitive alterations in other medical conditions, particularly by modulating neuroinflammation. However, their effect in obesity still remains poorly understood. Thus, we aimed here to evaluate if a n-3 PUFAs/AO supplemented diet improved mood and cognition in a genetic mouse model of obesity, and to identify the underlying mechanisms. Chronic supplemented diet consumption did not improve anxiety-like behavior, but reversed spatial memory deficits associated with obesity. This improvement, which occurs independently of any normalization of increased inflammation, may rather involve modulation of hippocampal neuronal plasticity. These findings suggest dissociation between the neurobiological mechanisms respectively underlying mood and cognitive alterations associated with obesity. They may help indentifying new targets for nutritional interventions aiming to improve health and quality of life of obese patients.