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BrinkZone Science Author
Brooke Morrisseau training


Within the realm of dietary supplements, weight loss supplements are one of the most popular categories. These supplements are used in an attempt to reduce body fat, as well as increase resting metabolic rate (RMR) [1]. In the United States, more than half of the adult population is now classified as overweight or obese [2]. White adipose tissue is the main site of excess energy storage in the form of triglycerides [3, 5, 39, 40]. Recent interventions have shown that various weight loss supplements and their ingredients have favorable effects on body composition [1], target adipose tissue, suppress appetite, and increase resting metabolic rate (RMR) [3].

Recent studies have suggested that the combination of thermogenic agents in a supplement can potentially increase caloric expenditure, RMR and energy metabolism [1,3-6]. A majority of thermogenic supplements contain some combination of herbal ingredients, usually some amount of caffeine, green tea extract, and combinations of herbal extracts  [7-9]. Caffeine is a central nervous system (CNS) stimulant [9,11] that enhances lipolysis and beta-oxidation [6, 9]. Weight loss supplements that don’t contain caffeine are known as non‐stimulant thermogenic agents. Non-stimulants enhance thermogenesis but don’t produce significant stimulation of the CNS [9,12]. The combination of ingredients within non-stimulant fat burners have been supported to increase RMR, speed up lipolysis through beta-oxidation, as well as reduce hunger and cravings [11].

Citrus Aurantium Fruit Extract is a derivative obtained from dried immature fruits of Citrus aurantium [12]. Citrus aurantium extracts that contain p‐Synephrine are used for weight loss, appetite control, as well as energy and mental focus [12].  p‐Synephrine enhances thermogenesis by binding to β‐3 adrenergic receptors, initiating lipolysis, which is the biochemical pathway responsible for the catabolism of triacylglycerol into fatty acids and glycerol [13-16, 30]. Naringin, a flavonoid derived from citrus grandis skin extract, has been shown to prevent low- grade inflammation [17], as well as regulate steps in carbohydrate and lipid metabolism [12]. Prior research has supported that naringin improves glucose and lipid homeostasis, and reduces adipose tissue inflammation in vivo [12,17-18], making it a desirable ingredient in many weight loss supplements. 

There is increasing interest in the potential role of Epigallocatechin gallate (EGCG), a polyphenol abundant in green tea extract (GTE), in fat metabolism and weight loss [19, 20].  EGCG is a form of catechin, which is found in green tea [24]. Although the precise mechanism of GTE in the human body is unclear, there is evidence to support that the ingestion of GTE can contribute to elevated fat oxidation and total energy expenditure [3, 20, 21, 27]. Specifically, the shorter term intake of GTE has been proposed to target the sympathetic nervous system [20], increasing catecholamine concentrations that stimulate lipolysis[20-21,23, 30]. 

5-Hydroxy-l-tryptophan (5-HTP) is a compound produced by the amino acid tryptophan, acts as a serotonin precursor, and is derived from Griffonia simplicifolia Seeds Extract). 5-HTP has been shown to suppress appetite in response to elevated stress [24], as well as decrease total daily food intake [24-26] by altering brain serotonin-mediated functions [24]. L-Tyrosine is another ingredient found in many weight loss products due to its role in enhancing catecholamine synthesis. Tyrosine is classified as a non- essential amino acid and a precursor of catecholamine hormones, such as the neurotransmitters dopamine, epinephrine and norepinephrine [28, 29]. These hormones play an essential role in initiating the process of lipolysis and fat oxidation [30]. 

Salicin is a substance found in foods, such as white willow bark, that is metabolized into salicylic acid [32, 34]. The idea behind Salicin’s use in weight loss supplements is that it can be combined with other ingredients to extend their activity, as well as reduce pain and inflammation [33,36]; Salicin reduces fatty acid oxidation when taken alone [35]. Hesperidin possesses inhibitory effects against obesity [37,38] via the production of adiponectin, which in turn activates the PPARa receptor initiating fat mobilization. When combined with other ingredients that are found in weight loss supplements, such as synephrine and naringenin, metabolic rate is increased [40]. Many weight loss supplements also contain forskolin, a substance that increases intracellular concentrations of cyclic adenosine monophosphate (cAMP) by activating an enzyme that converts ATP to cAMP, known as adenylyl cyclase. Foreskolin accelerates the process of ATP production, fat oxidation [41], and improves body composition [42].

While it is supported that the combinations of these ingredients have a positive influence on body composition, RMR, appetite, and fat oxidation, the magnitude of effect can vary based on the combination of ingredients. When choosing a supplement to aid in weight loss, you need to remember total caloric intake will be the driver of weight loss. Being in a total daily negative energy balance (calorie deficit), paired with a proper training and cardio plan, will be the first step. Second to this will be supplementation, which can aid in appetite suppression, initiate lipolysis, and speed up metabolism. 

Practical Application 

  • RMR = how many calories you burn at rest. The more muscle (lean body mass) you have, the higher this can be! 
  • Diet trumps supplementation. If your goal is fat loss, you need to be in a total daily negative energy balance. This can be made with total calorie intake, cardio, or a combination of both! 
  • 300-600 mg of caffeine per day taken in 200 mg doses can aid in fat loss. 


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