According to the World Health Organization (WHO), by 2050 two billion people will be 60 and older (WHO, 2021a) and by 2030, 1 in 6 people in the world will be aged 60 years or over (WHO, 2021a). With the increase in life expectancy, senescence-associated diseases like dementia (Lopez and Kuller, 2019) and loss of motor function (Wu, Ditroilo, Delahunt, and De Vito, 2021) are expected to increase. Some age-related metabolic and behavioral alterations, such as changes in physical activity and its patterns and spatial learning, may start to manifest earlier, in middle age (Benfato et al., 2017, Benfato et al., 2021, Quintanilha et al., 2021, Shoji et al., 2016, Stowie and Glass, 2015). With the adoption of the United Nation's (UN) Decade of Healthy Aging (2021–2030), countries have committed to 10 years of concerted and collaborative actions to improve the lives of older people (WHO, 2021b). In this way, research focused on aging should be stimulated and welcomed, including studies investigating when age-associated declines in physiological functions begin since they can set the adequate timing for interventions.

Animal models constitute an important tool to investigate age-associated decline deeply and mechanistically in several physiologic functions and the effects of interventions aiming to slow down this process. In mice, it has been shown that at middle age (10-15 months old), a period that precedes senescence (Flurkey and Currer, 2009, Flurkey et al., 2007), the first appearance of aging-related metabolic and behavioral alterations can be seen (Bayliak et al., 2021, Benfato et al., 2017, Boyer et al., 2019, Quintanilha et al., 2021, Shoji et al., 2016). Bayliak et al. (2021), demonstrated that middle age is a critical turn point in brain metabolism. They showed that in this phase of life, the oxidative stress markers start to increase, and the antioxidant defense decreases (Bayliak et al., 2021). Moreover, these alterations are not only exclusive to metabolism, since it is already known that there are behavioral changes that begin to happen in midlife. In a study performed by Shoji et al. (2016), it was observed that middle-aged mice had decreased social contact and impaired spatial learning and memory compared to younger animals (Shoji et al., 2016). Concerning anxiety, the results were controversial, since middle-aged mice exhibited increased anxiety-like behavior in the light/dark transition test, however, showed decreased anxiety-like behavior measured by the elevated plus maze test (Shoji et al., 2016).

As a way to delay aging, dietary manipulations have been tested (Erbaba, Arslan-Ergul, and Adams, 2020). They include a balanced diet of macro and micronutrients, supplementation of nutrients such as resveratrol, and caloric restriction (CR) (Ghosh, Sinha, and Raghunath, 2016). CR, with the absence of malnutrition, is the most effective known way of maximizing longevity in all species (Al-Regaiey, 2016, Kim et al., 2016, Martens and Seals, 2016). CR results in a consistent decrease in circulating levels of growth factors, anabolic hormones, inflammatory cytokines, and oxidative stress markers associated with several diseases (Longo and Fontana, 2010). In addition, CR is related to other biological changes including increased immunoreactivity of the neuronal activity marker ΔFosB in mice (Vialou, Cui, Perello, Mahgoub, Yu, Rush, Pranav, Jung, Yangisawa, Zigman, Elmquist, Nestler, and Lutter, 2011), protection against cognitive decline via up-regulation of brain-derived neurotrophic factor (BDNF) in diet-induced obese rats (Kishi, Hirooka, Nagayama, Isegawa, Katsuki, Takesue, and Sunagawa, 2015), and reduced age-dependent increase in oxidative DNA damage in Sprague–Dawley rats (Wolf, Fasanella, Tedesco, Cavallini, Donati, Bergamini, and Cittadini, 2005). Moreover, CR of 30% delayed premature aging and genomic stress in mice with DNA repair deficiency (Vermeij, Dollé, Reiling, Jaarsma, Payan-Gomez, Bombardieri, Wu, Roks, Botter, van der Eerden, Youssef, Kuiper, Nagarajah, van Oostrom, Brandt, Barnhoorn, Imholz, Pennings, de Bruin, Gyenis, Pothof, Vijg, van Steeg, and Hoeijmakers, 2016) and improved several metabolic and hormonal parameters that are implicated in the pathogenesis of type 2 diabetes mellitus, cardiovascular disease, and cancer; which are the main causes of mortality, morbidity, and disability in humans (Most, Tosti, Redman, and Fontana, 2016).

However, while several studies have already demonstrated the effects of CR in improving aging markers and extending longevity (Gensous et al., 2019, Pifferi and Aujard, 2019, Vermeij et al., 2016), it is not clear whether its benefit can be noted earlier, as in the beginning of middle-age, by initiating CR at young adulthood. This information can make interventions more accurate, as they will be aligned with the corresponding biological changes expected for a determined stage of life. Thus, taken together that central and behavioral age-related changes can be observed as soon as in early middle age, and the already consolidated benefits of CR, we aimed to determine whether long-term CR starting in adulthood could positively affect cognitive, neurochemical, and behavioral parameters at the beginning of middle age.