Fat-burning supplements are readily available over-the-counter and boast claims that you can lose weight without changing your diet or physical activity level.

Fat burners, also called thermogenics, are marketed as aids to help burn fat by increasing your body's metabolism, which refers to the rate at which you burn calories. However, scientific evidence supporting the safety and efficacy of most fat burners is lacking. In addition, some fat burners may cause dangerous side effects and others may not have metabolism-boosting benefits at all.

The Food and Drug Administration does not evaluate and test all fat burners on the market. Unfortunately, to have an edge, some manufacturers add ingredients that are not declared on the label, which could pose a serious danger. Annually, the FDA warns the public about dangerous undeclared ingredients it finds in fat burners.

In , the FDA identified more than 20 fat burners that contained dangerous ingredients. For example, one product contained sibutramine, a drug previously prescribed for obesity but removed from the market in due to increased risk for heart attack and stroke.

Another contained an unapproved laxative known to increase the risk of cancer. Yet another contained a selective serotonin re-uptake inhibitor, which is used to treat depression and can cause seizures and increase bleeding risk in people taking medications such as blood thinners.

Fat burners have long been linked to case reports of liver damage due to these products. In , an outbreak occurred that the FDA linked to one particular fat burner, which it subsequently removed from the market. The supplement caused nearly cases of hepatitis -- liver inflammation -- across the United States, according to a report published in the New England Journal of Medicine in April The supplement led to 47 hospitalizations, with three patients requiring liver transplants.

Information has not been released on whether the remaining hospitalizations resulted in permanent damage. In addition, one death was linked to this particular supplement.

A substance called aegeline is suspected of causing these adverse effects, according to the Centers for Disease Control. Aegeline also appears on labels under its scientific name, N-[2-hydroxy-2 4-methoxyphenyl ethyl]phenylpropenamide. This compound is extracted from leaves of an Indian plant called Marmelos Correa and has not been tested in humans for fat loss or exercise performance.

Many fat burners contain substances such as bitter orange, which may increase blood pressure and heart rate to levels that are not safe. All participants reported engaging in resistance exercise an average of four days per week.

The research protocol was approved by the University of South Florida Institutional Review Board. Following an explanation of all risks and benefits associated with the experimental protocol, each participant gave his informed consent to participate in this study.

Participants were screened for participation based on established criteria set forth by the American College of Sports Medicine [ 26 ]. In order to participate in the study, participants needed to be free from cardiovascular, pulmonary, and metabolic disease. Participants were also excluded as a result of any intolerance or known allergy to the supplement ingredients.

The study utilized a randomized, double blind, placebo controlled crossover design. Participants reported to the Performance and Physique Enhancement Laboratory following an overnight fast a minimum of an 8-h fast and a h avoidance of exercise on two occasions separated by at least 24 h.

After arriving to the laboratory, a coin was flipped to randomly determine the order of the dietary supplement ingestion. Testing sessions for both laboratory visits occurred between the hours of am and am, with the majority of all assessments beginning at 7 am.

Upon arriving to the laboratory, participants were encouraged to visit the restroom to void their bladders of urine. After sitting quietly for 5 min, participants had their resting heart rate and blood pressure recorded using an automated, oscillometric blood pressure monitor Omron 5 series Model BP, Lake Forest, IL, USA.

This method of automated, oscillometric blood pressure measurement has been validated in the scientific literature [ 27 ]. Heart rate and blood pressure were measured in triplicate and the average of the three readings was recorded.

Next, the participant remained in a reclined position for an additional 5 min prior to the resting metabolic rate RMR measures.

The device uses standard metabolic formulas to calculate oxygen uptake, and energy expenditure is calculated using a fixed respiratory quotient RQ of 0. Intra-day RMR ICC was 0. At baseline, two consecutive RMR tests were conducted and the lower of the two measured RMR values was recorded as the baseline RMR value.

During the RMR test, the participant was instructed to relax during the test, to breathe normally, and to remain as still as possible for the duration of the min test. The first 5 min of data collection was discarded [ 29 ] and the final 10 min of data collected was used in the calculation of the resting metabolic rate.

After ingestion of the supplement treatments, three more heart rate, blood pressure, and RMR assessments were conducted at 1-h, 2-h, and 3-h post ingestion. Figure 1 presents an overview of the study test sessions. Capsules were identical in appearance and taste.

Following the completion of two baseline RMR tests, the participant ingested three capsules of the thermogenic fat loss supplement or the placebo treatment with eight ounces of water. Supplement ingestion was in the presence of research personnel for all testing sessions.

Statistical analyses of the data were analyzed via a 2-factor treatment by time [2x4] within-subjects repeated measures analysis of variance ANOVA using SPSS version If sphericity could not be assumed, a Huynd-Feldt correction was used to produce a more critical F -value.

Post-hoc tests comparisons between treatments at each time point [baseline and min, min and min post ingestion and comparisons of post-supplement ingestion with baseline measures within each treatment were analyzed via paired samples t-tests. Incremental area under the curve AUC was calculated for each treatment thermogenic supplement and placebo using the trapezoidal method as described by Brouns et al.

AUC was determined by measuring the increase in RMR above baseline over the three-hour assessment period. A paired samples t-test was used to determine AUC differences between the two treatments. Skewness scores [displayed as statistic standard error ] ranged from 0. The standardized z scores skewness and kurtosis coefficients for both treatments were within the range of ±1.

Paired samples t-test revealed no significant difference in baseline RMR between the two treatments. No significant changes in RMR were observed for the placebo treatment in comparison with baseline values.

Change in resting metabolic rate RMR from baseline to 3-h post ingestion. Data is expressed as mean SD. Raw data for RMR and hemodynamic variables is summarized in Table 2. The aim of this study was to examine the effects of a multi-ingredient thermogenic fat loss supplement on RMR and hemodynamic function in resistance-trained males.

The observed increase in RMR occurred with a slight increase in SBP and DBP, while HR was not affected by the thermogenic supplement. Previous research has supported the idea that ingestion of thermogenic supplements containing caffeine in combination with various additional ingredients can acutely increasing RMR.

In the current study, the thermogenic fat loss supplement treatment experienced a greater elevation in RMR values compared to baseline, whereas the placebo treatment did not. Caffeine, in combination with other herbal ingredients, has been shown to increase RMR for up to three hours post ingestion [ 1 , 2 , 9 , 25 ].

In agreement with these findings, the current study demonstrated a significant 7. The placebo treatment, however, experienced only a 3. Caffeine is a popular ingredient used in many thermogenic supplements due to its ability to increase energy expenditure.

Caffeine alone [ 8 , 34 ], caffeine plus green tea extract GTE [ 7 , 34 , 35 ], and caffeine used in combination with other herbal ingredients [ 2 ] have been shown to significantly elevate RMR when compared to placebo.

Taylor et al. Furthermore, Wilborn et al. In agreement with these findings, Dalbo et al. While the increase in RMR observed in the current study was lower than that of previous studies, differences could be attributed to the dosages used, the combinations of ingredients, and the concentrations of individual ingredients.

The dose of caffeine in the current product mg was lower than that of the Taylor et al. and Wilborn et al. studies — mg , providing possible explanation as to the differences observed for RMR elevations.

Green tea extract, whether used on its own or in combination with caffeine, has been shown to increase RMR. However, the combination of GTE and caffeine can significantly increase catecholamine release which stimulates glycogen and triglyceride catabolism , leading to further increases in RMR [ 1 ].

Therefore, the observed increase in RMR in the current study is likely the result of the combination of the two stimulants. It is unlikely that L-carnitine played a role in increasing energy expenditure. While it may be possible that L-carnitine has an effect on fat metabolism after several months of ingestion, it is too early to draw any conclusions based on the acute dose used in the current study.

However, there was a slight, yet significant, increase in both systolic and diastolic blood pressure. It has been demonstrated that long-term consumption of caffeine has minimal effect on hemodynamic function [ 8 , 37 , 38 ]; however, there are some studies showing acute increases in blood pressure following ingestion of a thermogenic supplement [ 1 , 22 ].

Similar to previous studies, the present study observed a significant increase in blood pressure across time, with the dietary supplement treatment causing an increase in systolic blood pressure at both the and min time points and an elevation in diastolic blood pressure values over the three-hour testing period.

While ingestion of the thermogenic fat loss supplement caused elevations in diastolic blood pressure at the one and two hour postingestion time points, it is important to note that the diastolic blood pressure values remained within normal clinical ranges throughout the three-hour intervention period.

These elevations came with no adverse effects relative to resting heart rate and only slight increases in blood pressure values.

Although the thermogenic fat loss supplement resulted in an elevation in RMR, at this time we are not able to conclude whether this can lead to actual fat loss over time in this population. Future studies should investigate the effectiveness and safety of ingesting the dietary supplement over a longer period of time several weeks to determine if reductions in fat mass are observed.

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