A putative low-carbohydrate ketogenic diet elicits mild nutritional ketosis but does not impair the acute or chronic hypertrophic responses to resistance exercise in rodents

Abstract

We examined whether acute and/or chronic skeletal muscle anabolism is impaired with a low-carbohydrate diet formulated to elicit ketosis (LCKD) vs. a mixed macronutrient Western diet (WD). Male Sprague-Dawley rats (9-10 wk of age, 300-325 g) were provided isoenergetic amounts of a LCKD or a WD for 6 wk. In AIM 1, basal serum and gastrocnemius assessments were performed. In AIM 2, rats were resistance exercised for one bout and were euthanized 90-270 min following exercise for gastrocnemius analyses. In AIM 3, rats voluntarily exercised daily with resistance-loaded running wheels, and hind limb muscles were analyzed for hypertrophy markers at the end of the 6-wk protocol. In AIM 1, basal levels of gastrocnemius phosphorylated (p)-rps6, p-4EBP1, and p-AMPKα were similar between diets, although serum insulin (P < 0.01), serum glucose (P < 0.001), and several essential amino acid levels (P < 0.05) were lower in LCKD-fed rats. In AIM 2, LCKD- and WD-fed rats exhibited increased postexercise muscle protein synthesis levels (P < 0.0125), but no diet effect was observed (P = 0.59). In AIM 3, chronically exercise-trained LCKD- and WD-fed rats presented similar increases in relative hind limb muscle masses compared with their sedentary counterparts (12-24%, P < 0.05), but there was no between-diet effects. Importantly, the LCKD induced "mild" nutritional ketosis, as the LCKD-fed rats in AIM 2 exhibited ∼1.5-fold greater serum β-hydroxybutyrate levels relative to WD-fed rats (diet effect P = 0.003). This study demonstrates that the tested LCKD in rodents, while only eliciting mild nutritional ketosis, does not impair the acute or chronic skeletal muscle hypertrophic responses to resistance exercise.

Keywords: AMPK; low-carbohydrate diets; muscle hypertrophy; muscle protein synthesis.