Macronutrient manipulation has become a key nutrition component that, implemented in synergy with training, seeks to improve physical appearance, performance and human health. Among many dietary strategies that have been adopted, ketogenic diet (KD) is a subtype of low-carbohydrate and high-fat diet that needs to be planned considering special dietary features (such as the proportion of macronutrients) and physiological changes (ketosis generation). In view of the foregoing, KD should be planned from an objective perspective, checking for any increase in circulating ketone bodies (KB), a distinctive marker of physiological/nutritional ketosis. Main KB (acetate, acetone, and β-hydroxybutyrate) are produced in the liver under low-carbohydrate availability conditions, acting as an alternative energy source for peripheral tissue, such as skeletal muscle, brain and heart . To achieve a state of ketosis through a KD, carbohydrate intake should be reduced to a maximum of around 50 g per day, or 10% of total caloric intake during the day, while protein intake is moderate or high (e.g. ≈1.2 to 1.5 g∙kg− 1⋅d− 1). Remaining energy intake is predominantly from fats (≈60 to 80%), depending on the degree of displacement of carbohydrates and proteins .
Under normal conditions (with no KD diet or long fasting periods), the circulating KB values (β-hydroxybutyrate being the primary KB) are very low (<3 mmol∙L− 1); however, during physiological ketosis, as a result of the KD, ketonemia can reach maximum levels of ≈7–8 mmol∙L− 1 with no significant changes in blood pH . At this point, it is important to clarify the difference between physiological ketosis and diabetic ketoacidosis, where the concentration of KB in the blood can exceed ≈20 mmol∙L− 1, with a significant reduction in blood pH. In healthy population, the circulating KB values do not exceed ≈8 mmol∙L− 1, because the central nervous system uses these molecules efficiently as a source of energy, instead of glucose .
Several studies have focused on the effects of KDs on reducing body mass [5, 6], on improving health conditions, or as part of managing certain pathologies such as type 2 diabetes mellitus [7, 8], nervous system disorders such as epilepsy [9–11], and in different types/stages of cancer [12–16]. Currently, there is some controversy surrounding the advantages or disadvantages of KD for sports performance. It has been argued, on the one hand, that there are beneficial effects associated with the reduction of total body mass and body fat, a higher rate of fat oxidation, lower glucose oxidation and a reduction in the rate of muscle glycogen utilization during physical exertion, which represents an advantage in resistance exercise . On the other hand, physiological mechanisms have been cited that may limit performance in resistance training due to central fatigue, possibly because of increased circulation of non-esterified fatty acids which increases competition between these and tryptophan for albumin, resulting in an increase in free tryptophan, which in turn causes a greater absorption by the brain and subsequent augmentation of 5-hydroxytryptamine (serotonin) synthesis, a neurotransmitter linked to the feeling of lethargy and tiredness that may contribute to nerve signal losses at central level and a decrease in motivation. In addition, greater oxidation of amino acids can occur, which increases the concentration of ammonia, contributing to central fatigue . In general, several authors have also established that low-carbohydrate diets or KD do not seem to be superior or offer advantages for resistance exercise, compared with carbohydrate-rich diets [18, 19].
With regards to the effects of KD combined with resistance training (RT), such as muscle hypertrophy, there is even less information available, when compared with studies conducted on endurance-type performance. Even though KD can provide adequate quantities of proteins and calories necessary for muscle-protein synthesis induced by RT, they induce a state similar to fasting, prompting alterations in the metabolic pathways and molecular processes relating to autophagy and stress resistance , which consequently might hinder the building of muscle mass.
Considering the need to study on the effects of KD in resistance-trained subjects, the purpose of this study was to determine if following a KD hypercaloric diet would promote greater gains in fat free mass and fat loss during a hypertrophic training period in resistance-trained men. We hypothesized that a KD with caloric surplus in combination with RT in trained men would have a positive impact in fat reduction, and it would benefit the gains in lean body mass (LBM).