# Thermogenic Supplementation and Fat Loss in Resistance-Trained Males: A Randomized Controlled Trial
## 1 Introduction  
As interest in weight management and metabolic health continues to grow, many individuals rely on dietary supplements to enhance caloric expenditure and fat loss [1, 2]. Amongst the broad array of available supplements claiming to aid in this process, thermogenic supplements or \"fat burners\" have garnered significant attention in recentyears [1; 3; 4]. It has been previously reported that these multi-ingredient supplements [5; 6] may increase resting metabolic rate (RMR) [7; 8; 9; 10] which may contribute to enhanced energy expenditure and create the potential for fat loss when sustained over time. Despite these findings, direct evidence documenting reductions in fat mass specifically attributed to the use of thermogenic supplements is limited. Most studies have focused on acute effects on metabolism or surrogate markers of fat loss, leaving a gap in understanding their long-term efficacy in altering body composition [4; 8; 9; 10; 11; 12]. The effectiveness of thermogenic supplements may be related to the composition of their novel ingredients. Caffe, a primary ingredient of most thermogenic supplements, has demonstrated a thermogenic response via increased RMR [13; 14; 15; 16] and free fatty acid (FFA) utilization [13; 17; 18; 19] as well as potentially providing benefits to sports performance [19; 20; 21]. Prior studies have indicated the role of caffeine as a central nervous system (CNS) stimulant, providing physiological benefits in physique and weight management mediated by catecholaminergic upregulation and appetite suppression [16; 22]. When combined with other compounds, caffeine is believed to enhance metabolic and lipolytic effects by synergistically increasing energy expenditure and promoting fat oxidation [5; 7; 8; 9; 10; 11; 12]. This combination may amplify caffeine's stimulation of the CNS, leading to a more significant overall impact on metabolism. It is hypothesized that continued usage of caffeine-containing thermogenic supplements may subsequently support weight management and improve body composition by enhancing the body's calorie-burning capacity. In addition to caffeine, thermogenic supplements are formulated with compounds such as green tea extract. Green tea is valued for its high content of catechins, especially epigallocatechin gallate (EGCG), which works synergistically with caffeine to enhance its lipolytic properties [23; 24; 25; 26; 27]. These compounds are believed to stimulate the sympathetic nervous system, increasing energy expenditure and promoting the breakdown of stored fat [28]. L-carnitine is another ingredient in many thermogenic supplements due to its role in transporting long-chain fatty acids into the mitochondria [29; 30], where they are oxidized for energy [6; 29; 31]. This process is purported to support fat metabolism and energy production, particularly during exercise, which may potentially enhance endurance and facilitate fat loss. While some preliminary research suggests the use of maca and gymnema sylyvestre leaf extract, common ingredients in thermogenic supplements, potentially benefiting endurance and weight management, more research is needed to clarify their specific roles and effectiveness in enhancing physical performance and body composition [32; 33; 34]. While existing data may support the use of thermogenic supplements for fat loss and potential performance benefits, there is limited evidence on the efficacy and safety of these aids with chronic usage in conjunction with a resistance training program. The unique combination of ingredients commonly found in thermogenic supplements presents a promising approach to enhancing body composition and strength adaptations in trained and untrained populations.