Obesity has reached epidemic proportions in the United States (US) and worldwide [1]. For example, ~71% of the US population ≥20 yr of age are classified as overweight and/or obese, with ~42% of these individuals being in the obese category [1]. Notably, overweight and obesity are responsible for the total direct medical cost of approximately $260 billion in the US alone. More importantly, these conditions are well-known major risk factors for a wide spectrum of pathophysiological conditions and diseases, including various metabolic, cardiovascular, cerebrovascular, and neurocognitive conditions/disease states [1]. Furthermore, being overweight and obese are closely linked to various forms of cancer [2-8]. Accordingly, investigating strategies, including modifiable lifestyle behaviors, are critical for minimizing or preventing the aforementioned financial and pathophysiological conditions associated with overweight/obesity.

Historically, there has been no shortage of approaches utilized in an effort to combat the prevalence and/or detrimental health outcomes of being overweight/obese. These strategies include various pharmacological, surgical, and lifestyle behavioral approaches, which have demonstrated varying degrees of success [9-15]. The reasons for these mixed results are multifactorial, with an intricate web of factors, including time availability, ease of implementation, and numerous psychological, cultural, psychosocial, and physiological underpinnings. Of the many factors involved, the consumption of a healthier and/or low-calorie diet and augmented caloric expenditure in the form of increased physical activity (or a combination of these two approaches) are commonly recommended as the first course of action in terms of lifestyle behavioral modifications [12]. In recent years, the consumption of thermogenic caffeinated beverages (i.e., beverages that reportedly boost metabolism and increase fat burning) is growing in popularity [16-19]. There are many possible reasons for this increase, with the most commonly reported factors being the desire to increase energy levels, resting caloric expenditure, and resting metabolic rate while simultaneously reducing body fat [16,17,19-22]. Importantly, a unique potential benefit to the consumption of these beverages is that they are relatively inexpensive, and there are fewer “barriers” to implementation compared to other approaches such as diet and exercise; that is, they do not require a meaningful time commitment, specialized equipment, memberships, etc.

Despite this increase in popularity, there are limited well-designed, placebo-controlled studies aimed at assessing the impact of these beverages on well-validated indices of resting energy expenditure and resting metabolic rate. Accordingly, the primary purpose of this investigation was to assess the impact of acute consumption of a commercially available thermogenic caffeinated beverage on the indices of energy expenditure and substrate utilization in a cohort of healthy individuals. The secondary purpose was to examine the impact of a commercially available thermogenic caffeinated beverage on heart rate and arterial blood pressure. Comparisons were made relative to the placebo condition, in which all measures were repeated before and after consuming a similar volume of water. We hypothesized that consuming caffeinated thermogenic beverages would acutely increase indices of energy expenditure and fat utilization relative to water-alone conditions.

Ethical Approval: All procedures were approved by the Institutional Review Board of the University of Texas at Arlington (UTA IRB: 2024-0095). The participants were provided a verbal description of all procedures, purposes, and risks before providing written informed consent. This study conformed to the Declaration of Helsinki and is a registered clinical trial under the identifier NCT06330649 at www.clinicaltrials.gov.

Participant Characteristics: Thirty-two participants (17 females and 15 males) completed both conditions of the study. None of the participants reported being regular consumers of caffeinated beverages (i.e., coffee, energy drinks, or thermogenic beverages), as defined by consuming no more than two such beverages per week. Data collection was completed during two different visits to the laboratory, with each visit separated by a minimum of 24 hours (see below for detailed information about each study visit). All participants were normotensive, free of overt cardiometabolic or other diseases, nonsmokers, and did not currently consume vitamin- or mineral-based supplements. Participants were excluded if they were taking vasoactive medications or had overt cardiovascular, metabolic, or neurological diseases.

Study Visit Conditions: All outcome variables (see below) were assessed immediately before and at 30-minute intervals for 2 hours after consuming either a thermogenic caffeinated beverage or an equal volume of water. For the thermogenic beverage condition, participants drank a 12-oz can of a commercially available thermogenic beverage, Reign Storm Valencia Orange, which contains 10 calories and various ingredients, including 0 g of Total Fat, 280 mg of sodium, 5 g of total carbohydrate, 0 g of total sugar, 200 mg of plant-based caffeine, and 0 g of protein, as well as green tea extract (45% epigallocatechin EGCG), guarana, guayusa, and vitamins B3, B5, B6, B7, B12, zinc, and chromium. In the control condition, the participants consumed 12 oz of commercially available bottled water. All individuals participated in both conditions, and the order of drinking was randomized within each individual. Each day, the beverages were consumed within a 15-minute period. Visits were conducted at the same time of the day for each individual to minimize potential circadian influences on the outcome variables.

Instrumentation and Measurements: All data were collected following a minimum of 4 hours of fasting. Prior to each data collection visit, participants refrained from strenuous exercise and caffeinated or alcoholic beverages for a minimum of 24 hours, and all data were collected in a temperature-controlled laboratory (~24 °C and 40% relative humidity). The phase of the menstrual cycle was recorded but was not controlled. Upon arrival at the laboratory, participants voided their bladders, and their height and body mass were measured using a digital scale and standard stadiometer (Seca 769, Seca North America; Chino, CA, USA).

After sitting quietly in a recliner, each participant was instrumented for continuous measurement of heart rate (electrocardiography; CardioCard, Nasiff Associates; Central Square, NY, USA) and intermittent blood pressure of the brachial artery via an electrosphygmomanometer (Tango+, SunTech; Raleigh, NC, USA). At predetermined time points (see below), the participants were also fitted with a two-way valve mouthpiece and a nose clip (Hans Rudolph, Inc., Shawnee, KS, USA) connected to a metabolic cart (Parvo Medics True One 2400 oxygen uptake units; Sandy, UT, USA) to assess the indices of resting energy expenditure, pulmonary gas exchange, and substrate utilization via indirect calorimetry. The primary variables of interest were defined a priori as resting oxygen consumption normalized to body weight (ml/kg/min), and resting energy expenditure (REE) was calculated using the Weir formula, REE (kcal per day) = 1.44 (3.9 × VO₂) + (1.11 × VCO₂), which is commonly utilized to assess REE via indirect calorimetry [23]. Finally, substrate utilization was assessed as the respiratory exchange ratio (RER) [24]. The metabolic cart was calibrated according to well-validated guidelines recommended by the company prior to all data-collection visits. Briefly, the calibration included room-air and two-point gas calibrations. This process was followed by a 5-stroke calibration using a Hans Rudolf syringe and varying flow rates.

Data Analysis: The heart rate was continuously assessed throughout the duration of data collection during the study visit. Resting brachial blood pressure was measured in triplicate (⅓ systolic + ⅔ diastolic) at baseline (i.e., pre-beverage consumption), as well as at each post-beverage date collection time point (i.e., 30, 60, 90, and 120 minutes post consumption). Likewise, all the aforementioned assessments derived from the metabolic cart were performed at the same time points. Importantly, for each data collection time point, the participant was fitted with the mouthpiece and nose clip and breathed quietly for a minimum of 10 minutes (i.e., baseline, and 20-30, 50-60, 80-90, and 110-120 post-beverage consumption). Values are reported as the average measured during the last 5 minutes of each 10-minute period.

Statistical Analysis: The effect of Reign Storm Valencia Orange vs. water consumption on the measured variables was conducted using a two-way repeated measures analysis of variance (ANOVA) or a mixed-model analysis, with the main effects of beverage (i.e., Reign Storm Valencia Orange vs. water) and time (i.e., baseline, 30, 60, 90, and 120-minute post consumption). Tukey’s post hoc test was performed in the event of a significant interaction. All data were processed using the GraphPad Prism 10 software (GraphPad Software LLC, San Diego, CA, USA). The alpha value was set at p = 0.05.

This study was designed to test the hypothesis that acute consumption of a commercially available thermogenic beverage, Reign Storm Valencia Orange, would acutely increase indices of energy expenditure and fat utilization relative to the consumption of a volume-matched portion of water. The primary findings were that consumption of the thermogenic beverage resulted in: 1) an augmented increase in metabolism, as indicated by elevated oxygen consumption normalized to body weight, 2) an augmented increase in resting energy expenditure, and 3) a shift in substrate utilization during resting conditions, such that the body is more reliant on fat as its fuel source. Collectively, these results indicated that consumption of Reign Storm beverages appears to have a thermogenic effect that beneficially impact indices of resting energy expenditure and metabolism.

Owing to the prevalence and detrimental physiological outcomes associated with being overweight and obese [1], a great deal of attention and scientific research has been geared towards identifying approaches to combat this public health concern. One approach that has demonstrated positive results in recent years is the consumption of thermogenic beverages [20-22]. The current study was not designed to assess the role of specific ingredients associated with the observed increases in resting energy metabolism or fat utilization. Reign Storm beverages are commonly consumed thermogenic beverages that contain a variety of ingredients, including 200 mg of plant-based caffeine and a proprietary blend of green tea extract (45% EGCG), guarana, guayusa, vitamins B3, B5, B6, B7, B12, zinc, and chromium. It is well-documented that caffeine elevates resting energy expenditure, caloric consumption, and fat oxidation in both normal-weight and obese populations. The most likely mechanistic pathways through which caffeine exerts these effects is through stimulation of β₂ and β₃ adrenergic receptors [17,19,25] as well as elevations in circulating epinephrine concentrations secondary to activation of the CAMP signaling pathway [17,19]. Similarly, green tea extracts commonly contain EGCG and guarana, and guayusa also contain caffeine. Notably, these ingredients, either individually or in combination, have been demonstrated to increase resting energy expenditure and fat utilization thus likely partially explaining the beneficial effects of green tea extract [17,26]. Accordingly, the combination of ingredients in the Reign Storm beverage appear to result in the observed increase in resting energy expenditure, caloric consumption, lipolysis, and fat utilization in the current study. To this end, in the current study, resting energy expenditure was elevated by approximately 8-14% for up to 2 hours following Reign Storm beverage consumption, which is consistent with previous reports [17].

It has been fairly well established that caffeine induces acute elevations in arterial blood pressure in the order of ~5 mm Hg, likely secondary to peripheral vasoconstriction and, thus, elevations in total peripheral vascular resistance [27-30]. In contrast, the impact of acute consumption of thermogenic beverages on arterial blood pressure is equivocal, with reports indicating increases [31-33] or no effect [34-36]. In the current study, we observed increases in systolic, diastolic, and mean arterial blood pressure for up to 2 hours following the acute consumption of Reign Storm Orange Valencia. Importantly, a similar magnitude of elevation was observed following the consumption of a similar volume of water. The acute elevations in arterial blood pressure could be related to the natural circadian pattern of blood pressure, which gradually increases throughout the course of the day [37]. Another possible explanation could be related to the acute hypertensive effect of the liquid. In this regard, an acute increase in both systolic and diastolic blood pressure has been observed in both hypertensive and normotensive individuals following the consumption of approximately 16 oz of water [38]. This response is likely related to increased sympathetic nervous system activation, which results in elevated arterial blood pressure through various pathways [38,39]. While these studies [38,39] only assessed the impact of water consumption on arterial blood pressure and sympathetic nervous system activation, it is reasonable to speculate that the impact is related to plasma volume as opposed to pure water, a finding that may explain the findings of the current study. Similarly, the impact of caffeine and/or thermogenic beverage consumption on the heart rate has been the focus of numerous research studies [27-29]. Notably, these findings are inconclusive, with numerous studies reporting directionally different responses [27,30,40]. In the current study, we observed a significant reduction in heart rate for up to 2 hours following the consumption of both the Reign Storm Orange Valencia beverage and water. Importantly, the magnitude of the reduction was similar between the beverage conditions. The most likely explanation is related to the reflex increase in cardiac parasympathetic nervous system [41] activity secondary to the aforementioned elevations in systolic, diastolic, and mean arterial blood pressures that occurred under both beverage conditions.

The primary purpose of this study was to assess the effect of consuming a commercially available thermogenic beverage on energy expenditure and substrate utilization. Accordingly, by design, we could not isolate the reported effects of any of the specific ingredients in Reign Storm beverage. However, this represents a more practical approach, given that we utilized a beverage that can be easily purchased in the United States and worldwide. While the results demonstrate a beneficial effect of Reign Storm beverage consumption on the indices of resting energy expenditure and substrate utilization, additional studies may be conducted in a larger and more heterogeneous cohort of individuals.

In summary, these results indicate that consumption of Reign Storm beverages appears to have a thermogenic effect that results in a beneficial impact on indices of resting energy expenditure and metabolism. Additionally, these results demonstrate that consumption of the Reign Storm beverage results in a shift in fuel source utilization during resting conditions, such that the body is more reliant on fats, and Reign Storm also accelerates metabolism. Accordingly, these findings demonstrate that the consumption of Reign Storm beverages in combination with other modifiable lifestyle behaviors, such as exercise and a healthy diet, appears to help to lose body weight and burn fat.