There are two main types of fat burners: those that contain stimulants and those that are free of stimulants.
Most (but not all) thermogenic fat burners contain stimulants that usually contain caffeine. Caffeinated fat burners are good for people who find it hard to summon up the energy for an intense workout or a long cardio session.
[Caffeine] Helps burn fat and helps athletes stay longer in the gym and more in sports, "explains Robert Wildman, RD, in the article" Boost Your Workout with Coffeine. "
Caffeine is also a strong appetite suppressant for Yes, there's a very good reason that it's such a popular ingredient in fat-burning supplements!
As effective as caffeine is, it's by far not the only ingredient in popular fat burners, and it gets even more effective when combined with some others.
But to be clear, just because a fat burner has more ingredients does not make it any better! If you are unfamiliar with fat burners, you should concentrate on a few essential ingredients like this.
Green Tea: It has been shown that extracts of green Te e and green tea activate the body thermogenic fat burning activity. A study published in the American Journal of Clinical Nutrition found that men taking the active ingredient in green tea (catechins) significantly reduced their total fat area, waist circumference, skinfold strength, and subcutaneous fat area.  As the exercise physiologist Nick Coker explains in the article, "Your Competent Guide to Green Tea," it has been shown that taking this ingredient with caffeine is even more effective.
L-Carnitine: This stimulant-free amino acid has been the secret weapon for physicists for decades. Once taken once or twice a day, it can help your body convert stored body fat into energy, making you leaner and more defined. This is done by breaking up fatty acids so the body can use them as fuel. As Jim Stoppani, Ph.D., explains in "Your Expert Guide to L-Carnitine," studies have also shown that it helps post-workout recovery, reduces muscle damage, and even reduces muscle soreness caused by exercise.
CLA: Conjugated linoleic acid (CLA) is a naturally occurring fatty acid similar to an omega-6 fatty acid. Although CLA is a fat, studies show that consuming 1.4 to 3.0 grams per day in total can lead to fat loss. [3,4] It can also help you maintain your muscles during periods of weight loss, as the kinesiologist Ciaran Fairman explains in the article "Your Expert Guide to CLA." Remember, muscle is your ally for long-term success!
Yohimbine: This ingredient, made from the bark of the yohimbe tree, is a popular stimulant in fat burners. A well-known study has shown that it leads to significantly better fat loss results for well-trained football players than placebo.  However, more research is definitely needed, and Yohimbin is not for everyone! If you are prone to anxiety or are very sensitive to stimulants, use caution with yohimbine. Some people find it very nervous or anxious.
Garcinia Cambogia: As the nutritionist Jonny Bowden, Ph.D., explains in the article "Fat Loss Hope or Hype: The Truth About Garcinia Cambogia" This caffeine-free sour fruit extract has been very popular in recent years become popular. As long as you take it properly, it can provide strong appetizing benefits.