Recent years have seen a rise in clinical and scientific interest in dietary interventions for the management of psychiatric conditions, such as major depressive disorder (MDD) and anxiety [1], [2], [3], [4], [5], [6], [7], [8]. Specifically, the ketogenic diet (KD), which has already been proven to be effective in treating epilepsy [9], has drawn interest in treating psychiatric conditions and enhancing cognitive function in healthy people [10], [11], [12]. In particular, KD-fed rats showed shorter periods of immobility in the forced swimming test, a traditional behavioral paradigm used to measure depression levels in response to acute stress when compared to rats fed the control diet [1]. Another study discovered that CD-1 mice fed with KD during the prenatal period in utero showed decreased susceptibility to anxiety and depression [13]. In addition, the KD has also been suggested as a potential metabolic therapy for neurological diseases such as mitochondriopathies [14], alternating hemiplegia of childhood [14], brain tumors [14], migraine [14], autism spectrum disorder (ASD) [14], Alzheimer's disease (AD) [15], Parkinson's disease (PD) [16], multiple sclerosis [17,18], alcohol dependence [19], traumatic brain injury [20], schizophrenia [21] and substance use disorders [22].

A typical KD has a lipid content of up to 80%, adequate protein, and low carbohydrate levels. In contrast to a standard diet high in carbohydrates, where glucose powers most tissues, including the brain, a KD regimen drives the body into a metabolic state called ketosis, where fats are transformed into ketone bodies, like BHB and acetoacetate (AcAc) [23]. Fatty acids and ketone bodies are catabolized to produce energy, with ketone bodies being particularly important for the brain. Under normal homeostatic conditions, the metabolic modifications brought by a KD regimen may have positive effects on physiological and cognitive functions [11]. A KD may therefore be a viable strategy to prevent the development of mental illnesses in otherwise healthy people, especially in light of preclinical data that suggests a KD increases resistance to stress-induced depression [7].

The prefrontal cortex (PFC) holds a vital role in the regulation of emotional states in coordination with other neural centres such as the amygdala and hippocampus [24]. The dysregulation of PFC has been implicated in the etiology of anxiety, depression, and mood disorders [25]. Numerous studies display structural and functional alterations within the PFC and hippocampus among individuals with anxiety and depression. For example, increased neuroinflammation, disrupted glutamatergic, and gamma-aminobutyric acid transmission, neuronal loss, lowered synaptic markers, reduced dendritic spine density, and PFC volumetric reductions have been consistently observed in anxiety and depressive patients [26], [27], [28]. These findings suggest the critical involvement of the PFC and hippocampus in anxiety and related disorders.

Recent studies overwhelmingly demonstrate sex differences in the metabolic effects of the KD. For example, Sprague Dawley rats fed with the KD and ketone diester for 2 weeks showed a sex-specific increase in circulating ketone bodies with a concomitant decrease in the body weight and blood glucose levels [29]. In another study, sex-specific beneficial effects of the KD were observed in rats after pre-exposure to a high-fat, high-sugar diet [30]. However, there is some evidence to suggest that the beneficial effects of KD in improving metabolic health are sex-specific but whether the effects of KD on anxiety-like behavior are also sex-specific is unclear. Moreover, underlying molecular mechanisms contributing to these effects such as neuroinflammation are also obscure needing further research on these lines. Therefore, the present study aimed to explore the sex differences in the neuroimmune and anxiety-like responses to KD in healthy male and female mice.