Thermogenic supplements, also known as thermogenics, are a popular category of health supplements that aim to aid in weight loss. Aptly named, thermogenics have been found to increase basal metabolic rates – thus “creating heat.” However, the safety of thermogenics has been heavily debated.
Just like most health supplements, the safety of thermogenics highly depends on their active ingredients. Substances such as ephedrine and DMAA have previously been used in thermogenic supplements but have since then been banned by the FDA. However, thermogenics utilizing other ingredients such as caffeine, green tea extract, and cayenne powder have been studied to be generally regarded as safe for moderate consumption.
A thermogenic is any substance that can elicit thermogenesis, the the body’s natural way of converting nutrient calories into heat energy. This process is integral for homeostasis – the body’s system for maintaining its internal, chemical, and physical conditions. Particularly, thermogenesis is essential for thermoregulation and body weight control (1).
Thermogenic substances function through the stimulation of the central nervous system, through metabolic mechanisms, or a combination of the two.
Examples of stimulatory thermogenic substances include ephedrine and caffeine while non-stimulatory thermogenic substances include bitter orange, capsaicin, and green tea extracts.
Thermogenics, also known as fat burners in the supplement industry, are often touted/marketed as "weight loss supplements."
Different studies have been conducted to evaluate the effectiveness of thermogenic supplements. Undeniably, thermogenics have been observed to induce certain physiological changes such as oxygen uptake, pulmonary ventilation, carbon dioxide output, respiratory exchange rate, energy expenditure, heart rate, systolic blood pressure, and diastolic blood pressure (2).
However, thermogenics are still being debated as to their effectiveness as a weight loss aid because of conflicting results from academic studies.
Many studies have observed statistically significant effects in weight loss due to thermogenic supplements. For example, reviews done on green tea extract have been associated with weight loss due to diet-induced thermogenesis (3). However, meta-analyses have also shown green tea to induce statistically insignificant weight loss (4).
Thermogenic supplements containing caffeine as their active ingredient have received relatively positive academic conclusions. Caffeine has been comprehensively studied to show it promotes fat oxidation (5). Furthermore, caffeine has also been associated with success in weight loss maintenance (6).
However, it is debated that studies conducted over short time periods can only imply the short-term effectiveness of thermogenic supplements on weight loss. Limited studies have been done on the effectiveness of thermogenics for long-term weight loss.
Different thermogenic supplements come with varying active ingredients. This is where the safety of these supplements is tied to. Sources note that there are common ingredients that have already been studied to be generally safe for consumption. These include caffeine, green tea extract, capsaicin, and garcinia cambogia.
Recent studies have also looked into the potential of other substances such as sunflower oil, coconut oil, and conjugated linoleic acid (7).
These ingredients have been generally regarded as safe and side effects associated with these ingredients are typically mild at most.
However, caution is recommended when using thermogenic supplements that use caffeine as their active ingredients due to the amount of caffeine present in their recommended dosage. The FDA cites that healthy adults can intake up to 400 milligrams of caffeine per day without any adverse health effects; This can be equated to 4-5 cups of coffee (8).
If you are a coffee drinker, it is important to take the amount of caffeine into consideration when consuming caffeinated thermogenic supplements as well. Thermogenics using caffeine as their active ingredients typically have high concentrations of caffeine. Exceeding the 400-milligram limit might risk people more to side effects such as palpitation, anxiety, headache, restlessness, and dizziness (9).
Furthermore, some thermogenics can induce slight elevations in blood pressure. Caution should be observed, especially for individuals with increased risk of hypertension.
Controversially, some ingredients found in thermogenic supplements have been found by the various governing bodies to be unsafe. Here are some ingredients to look out for when choosing a thermogenic supplement.
A major component in traditional medicine, ephedra has been found to be historically used in diverse cultures ranging from traditional Chinese medicine to native Americans.
Entering the health supplement market as a weight loss solution in the 1990s, ephedra has since then been scrutinized by numerous studies showing associations between ephedra use and a host of adverse health effects such as hypertension, cardiac dysrhythmias, myocardial infarction, seizure, stroke, and even sudden death.
After receiving more than 1,800 adverse-event reports, the FDA banned the sale of ephedra-containing products in 2004 (10).
Originally trademarked in 1948, DMAA (1,3-dimethylamylamine) has been used in numerous performance boosting and weight loss supplements. Although lacking in pharmacokinetic studies to elucidate its mode of action, many individuals have reported that DMAA results in elevated body temperature suggesting its thermogenic capacity (11).
DMAA was officially banned by the FDA in 2012 due to the absence of any reliable scientific evidence supporting its effectiveness and due to the health risks it presents. As a vasoconstrictor, DMAA can narrow blood vessels which can lead to raised blood pressure and cardiovascular problems ranging from shortness of breath and tightening in the chest, to heart attacks (12).
People looking through thermogenic supplements should be wary of DMAA because the compound can be listed as one of the following: 1,3-DMAA, 1-3,dimethylamylamine, 1,3-dimethylpentylamine, 2-amino-4-methylhexane, 2-hexanamine,4-methyl-(9CI), 4-methyl-2-hexanamine, 4-methyl-2-hexylamine, dimethylamylamine, geranamine, methylhexanamine, and methylhexanenamine.
Extracted from the bark of an African evergreen tree (Pausinystalia johimbe), yohimbe is an herbal supplement that has a long history in traditional medicine.
Unlike ephedra and DMAA, yohimbe is an FDA-approved substance that can be found in erectile dysfunction drugs. Aside from medical applications, yohime has also been promoted and used in supplements for athletic performance, high blood pressure, diabetic neuropathy, angina, and weight loss (13).
However, studies have still found evidence associating this substance with adverse health effects such as heart attacks and seizures. Furthermore, despite FDA approval, this substance has been banned in several other countries outside of the US such as Canada, Australia, and the United Kingdom.
Like yohimbe and ephedra, bitter orange is a common ingredient in health supplements with a long history in traditional medicine. Extracted from the immature fruit or peel of the bitter orange (Citrus aurantium), bitter orange extract contains p-synephrine – a protoalkaloid that has been studied to influence certain physiological conditions (14).
The principal constituent of bitter orange, p-synephrine, has stimulatory effects on the central nervous system. Additionally, the substance also increases blood pressure and heart rate. Both of these physiological effects add up to the thermogenic capabilities of bitter orange extract.
Much confusion revolves around bitter orange extract due to conflicting statements regarding its safety. While there is insufficient evidence to support any adverse health risks associated with the consumption of bitter orange, many reports cite that the effects of the extract on blood pressure and heart rate can lead to potential cardiovascular hazards.
Until the literature reaches a consensus regarding the safety of bitter orange, it might be best to remain cautious regarding this ingredient.
Overall, thermogenic supplements are safe to consume when they are developed with regulated and approved active ingredients. Furthermore, moderate consumption should be observed because of the safety limits of certain substances such as caffeine. Safely and effectively utilized, thermogenic supplements may exhibit high potential for aiding weight loss.