Methodological Issues Related to Exercise Interventions during Fasted or Fed State Response

Abstract

We thank Dote-Montero and Amaro-Gahete [1] for their comments and thoughts regarding the nutritional standardization methodology described in our study [2]. The role of pre-exercise nutrition in modifying substrate oxidation rates during exercise is well known in literature. Yet, in the acute exercise phase, it is mainly exercise intensity that dominates substrate oxidation irrespective of training status or dietary intake [3]. Moreover, and different from healthy individuals, patients with type 2 diabetes mellitus (T2DM) are mostly characterized by a reduced metabolic flexibility, resulting in low variability in respiratory exchange ratio for marked changes in insulin levels [4]. The short-term effect of the pre-exercise evening meal composition or the fasting duration on fasting glycemia/insulinemia might be limited [5], but remains questionable in T2DM patients and thus warrants more research. In our study [2] patients selected their own breakfast (type and amount) on the exercise days, and therefore the meal was not standardized for either energy content or carbohydrate content. These breakfasts were repeated throughout the entire intervention to obtain some degree of standardization on the exercise days. Patients in the fasted exercise group began their training after an overnight fasting period (at least 10 hours of fasting; no upper limit defined). Aside from different fasting durations, standardizing pre-exercise meals (with defined composition and energy content) will definitely alter metabolic responses, as some patients will be undernourished and others will be overfed compared to their habitual diet. Therefore, in terms of external validity and real-life situations, it is hard to generalize a pre-exercise evening meal. With regard to optimal exercise-nutrition interaction, altering meal timing should be actively attempted in exercise intervention studies instead [6]. We agree with Dote-Montero and Amaro-Gahete [1] that standardization of pre-measurement conditions is imperative. In our study [2], two separate laboratory visits were included, each requiring specific preparation guidelines. Patients were asked to abstain from alcoholic and caffeinated drinks for 48 hours, to perform no exercise or any other moderate/vigorous physical activity within the last 72 hours and to have their latest meal (mostly lunch) at least 2 hours