<p>Exercise Training and Fasting: Current Insights</p>

Abstract

Fasting is defined as the abstinence from consuming food and/or beverages for different periods of time. Both traditional and modern healthcare systems recommend fasting as a therapeutic intervention for the management of several chronic, non-infectious diseases. Exercising during a fasting state increases lipolysis in adipose tissue while also stimulating peripheral fat oxidation, resulting in increased fat utilization and weight loss. A key focus of this review is to assess whether endurance training performed while fasting induces specific training adaptations, where increased fat oxidation improves long-term endurance levels. Fasting decreases body weight, lean body and fat content in both trained and untrained individuals. Several studies indicate a broader impact of fasting on metabolism, with effects on protein and glucose metabolism in sedentary and untrained subjects. However, there are conflicting data regarding the effects of fasting on glucose metabolism in highly trained athletes. The effects of fasting on physical performance indicators also remain unclear, with some reporting a decreased performance, while others found no significant effects. Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant findings. Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high intensity training while fasting.

Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis

“…Moreover, fasting triggers numerous hormonal adaptations culminating in enhanced metabolic rate and preserved lean mass (e.g., increased serum levels of noradrenaline and growth hormone) [46]. In addition, exercising while fasting increases the expression of sirtuin 1 (SIRT1) and phosphorylated AMP-activated protein kinase (AMPK), which have numerous effects on gene expression (i.e., regulation of mitochondrial biogenesis) [54]. This is important because there is undisputed evidence that, to improve athletic performance, it is fundamental to achieve an optimal balance between lean and body fat mass [54].…”

“…In addition, exercising while fasting increases the expression of sirtuin 1 (SIRT1) and phosphorylated AMP-activated protein kinase (AMPK), which have numerous effects on gene expression (i.e., regulation of mitochondrial biogenesis) [54]. This is important because there is undisputed evidence that, to improve athletic performance, it is fundamental to achieve an optimal balance between lean and body fat mass [54]. Nevertheless, some authors argue that it is necessary to pay attention to the general protein content that is ingested during feeding hours, as well as the final energy balance achieved on a daily basis [3,22].…”

Ramadan 2020 and Beyond in the Midst of the COVID-19 Pandemic: Challenges and Scientific Evidence For Action

“…The available data suggest that exercise in a fasting state decreases body weight and fat mass, although more controlled studies are needed for definitive recommendations to be made [85]. A moderate intensity exercise during fasting is recommended for the prevention of hypoglycemia.…”

“…Training in the evening compared to training in the morning while fasting may be more effective in enhancing aerobic performance. Athletes may wish to train in the fasting state in the preseason as fasting increases the activity of fat-burning enzymes [85]. However, fasting can elicit negative effects on performance in some events, and hence modifications to the training schedules, for example, fasting during the preseason, may minimize such effects [85].…”

Effects of fasting on the expression pattern of FGFs in different skeletal muscle fibre types and sexes in mice

“…Studies show that fasting has several healthy benefits [8], such as increasing longevity, alleviating obesity and other non-infectious diseases [9], and anti-tumour [10]. However, fasting can also lead to muscle wasting and cause life-threatening problems [11].…”