Natural Fat burner: Citrus aurantium
Most people who have ever tried a fat burner would have, unknowingly, consumed Citrus Aurantium (CA). It is not the main ingredient of most fat loss supplements but let us delve into why it is thought to be a fat burner.
As stated in the name, CA is a small citrus tree responsible for producing Seville oranges. The fat loss compounds of CA are derived from the inedible portion of the immature fruit. Synephrine and Octopamine are found in these inedible portions. Both of the two aforementioned compounds work similarly to ephedrine (Find this article). Synephrine is the more active compound and is known to stimulate Beta Receptors, more specifically the beta 3 receptor. The Beta 3 receptor stimulate burning of fat and increases in metabolic rate.
In practice, however, data is limited. There have not been many studies in regard to the side effects or efficacy in weight loss. In the only study that I could find, it was used at 975mg with 528mg of caffeine in individuals and resulted in 0.5kg more weight loss than the placebo. However, this is when it was combined with caffeine and does not show whether it is effective.
In conclusion, there is limited data on CA, however, mechanistic evidence would suggest that it could be effective for weight loss.