The purpose of the present study was to determine the effects of Meltdown, a commercially available thermogenic nutritional supplement, on HR, BP, REE, and RER before, during, and after exercise. The results of this study show that Meltdown supplementation significantly elevated REE up to 120 min post-ingestion, while also decreasing RER up to 60 min post-ingestion. However, no significant differences were observed between Meltdown and placebo after a bout of maximal treadmill exercise, which was conducted 75 minutes after supplementation. In addition, no significant differences between Meltdown and placebo were observed for HR or BP before, during, or after exercise. Therefore, the symathomimetic compounds within Meltdown were not associated with any differential effects on hemodynamic function during exercise.
Thermogenic supplements may increase REE and fat metabolism through activation of the β2 and β3-AR. β2-AR stimulation has also been shown to up-regulate uncoupling proteins in skeletal muscle, which may have a significant impact on whole body thermogenesis [17, 18]. Furthermore, the β3-AR, located primarily on adipocytes, enhances lipolysis and thermogenesis. It has been determined that beta-AR agonists with high thermogenic, antiobesity, and antidiabetic activities are potent stimulators of the β3-AR . Given that the stimulation of the β3-AR primarily promotes lipolysis, it appears to be a good target for weight management and obesity treatment.
Previous studies examining the efficacy and safety of several alleged thermogenic compounds such as caffeine, citrus aurantium, garcinia cambogia, green tea extract, and ephedra have been conducted [5, 6, 12, 20–24]. Moreover, studies involving ephedra or ephedra/caffeine revealed that that these compounds, especially in combination, may have significant potential to increase daily energy expenditure. In fact, the ephedrine/caffeine combination is reported to increase energy use 37.4–114 kcal/day more than placebo [21–24]. For example, one study investigated the changes in REE for three hours following the administration of 150 mg of caffeine and herbal ephedra containing 20 mg of ephedrine alkaloids . During the final 30 min of measurement, REE was 8.5 ± 2.0% higher (P < 0.05) in the caffeine/ephedra trial compared to the placebo trial. A significant increase in REE was observed for caffeine/ephedra 180 min post-ingestion (1.47 ± 0.10 vs. 1.34 ± 0.08 kcal/min). In the present study, Meltdown supplementation, as compared to placebo, induced an increase in REE at 60 min post-supplementation (1.49 ± 0.28 vs. 1.30 ± 0.22 kcal/min) comparable to the previously-mentioned ephedra/caffeine study . Since Meltdown contains compounds with β-agonist activity, in comparison to previous studies [21–24] Meltdown may generate REE increases comparable to ephedrine, even though in the present study the increases were observed to occur approximately 120 minutes earlier.
Furthermore, another study revealed that Java Fit, a combination herb and coffee supplement product, containing green tea extract, garcinia cambogia and niacin, produced a 14.4% increase (1,858.23 ± 412.89 vs. 2179.75 ± 424.34 kcal/day or 1.29 ± 0.29 vs. 1.51 ± 0.29 kcal/min) over the baseline resting energy expenditure value three hours after administration in physically active adults . This difference was significantly more than a 5.7% increase observed with a commercially available caffeine-containing coffee. On the other hand, no significant changes were observed in RER during this study, and no significant changes in HR or BP were observed for either coffee product. In addition, another study conducted with Java Fit coffee concluded that this product has no negative effect on hemodynamic function and may increase REE in individuals who are sensitive to caffeine and herbs contained within the coffee supplement . Therefore, the results of these two studies indicate that a mixed herbal product containing caffeine, green tea extract, garcinia cambogia and niacin induced a significant increase in energy expenditure without a simultaneous increase in hemodynamic safety variables in a young, fit population.
In addition to overall energy use, the use of fat as a source of energy, as indicated by an RER close to 0.7, is also of interest in metabolic studies. Furthermore, greater use of fat as an energy source is also presumed to be favorable. In fact, a study of 775 healthy, non-obese young men revealed that a high fasting RER (> 0.86) is a predictor of weight gain in men with an initial BMI < 25 . Therefore, a product that lowers RER may be beneficial for lean men. Respiratory exchange ratio was significantly decreased with Meltdown, as determined by AUC analysis. Since REE increased and RER decreased, the data suggest that the Meltdown supplement increased energy expenditure with a reliance on fat as the preferential source of substrate oxidation.
Though ephedra and caffeine combination products increase metabolic activity [21–24], products of this kind are also associated with increases in blood pressure and heart rate. For example, one study of 15 healthy, young (aged 26.7 ± 2.52 years) male and female participants revealed that a single dose of a Metabolife 356, which included 12 mg of ephedra and 40 mg of caffeine, resulted in increases in the mean maximal QTc interval and systolic BP. As such, there is concern that combination products designed to mimic the effects of the ephedra and caffeine will also cause significant increases in HR and BP . Such an increase in HR and BP was observed in a study comparing placebo to Xenadrine EFX, a 19-component combination product containing both caffeine and synephrine . Therefore, the concern that so-called ephedra-free thermogenic products may increase BP appears to be legitimate; however, the results of the present study do not suggest that Meltdown increases hemodynamic safety markers. On the other hand, the present study was conducted in apparently healthy, lean young men; therefore, the results may not translate to obese or morbid populations.
On the other hand, the individual components used in thermogenic supplement formulation often do not have significant effects on BP or HR. For instance, a previous study also showed that a 46.9 mg dose of synephrine alone does not raise BP or HR more than placebo in healthy adults . Though caffeine is thought to have a pressor effect, as evidenced by some reviews and meta-analysis [30, 31], previous research indicates that caffeine alone may not increase the HR or BP of healthy, young, non-obese participants aged 21–26 . Specifically, during one investigation 11 male and female participants ingested a caffeine dose of 5 mg/kg body weight or placebo . The caffeine dose caused notable side effects and a significant inotropic effect (as assessed by echocardiogram); however, no increases in HR or BP were observed. On the other hand, another study of 10 healthy men aged 21–39 showed that a bolus dose of 0.125 mg/kg dose of yohimbine increased BP significantly ; however, HR was not affected. In the present study, the Meltdown supplement did not significantly elevate HR and BP before, during, or after exercise, which suggests that ingestion of this thermogenic supplement does not appear to adversely affect hemodynamic responses.
In conclusion, these data presented herein suggest that Meltdown enhances fat oxidation and REE more than placebo for up to 60 min and 120 min, respectively, after ingestion in fully rested and post-exercise states without any adverse hemodynamic responses when administered to apparently healthy young men.