What exactly are thermogenic fat burners?

Thermogenic fat burning supplements contain natural ingredients which are purported to boost metabolism and increase fat burning. In fact, thermogenic literally means heat-producing. When your body burns calories it generates more heat, so supplements which increase energy expenditure are considered thermogenic.

Some of the most popular options, which tend to dominate the nutritional supplement market, include caffeine, green tea extract (catechins), capsaicin, and yohimbine. All of these ingredients are considered to have a thermogenic effect to some extent and are consequently marketed as aids to weight loss generally and fat burning more specifically.

Let’s take a look at some of these active ingredients in a little bit more detail and explain why supplementing with them might help you to achieve your weight loss and fat burning goals!

Why should you take thermogenic supplements?


By far the most common and effective thermogenic ingredient has to be caffeine. Naturally found in over 60 plant varieties including coffee (40mg per 100g), cocoa, tea and yerba mate, caffeine is an alkaloid derivative, peaking in the blood around 30-90 minutes after ingestion. The vast majority of the caffeine you consume is metabolised, with only 1-3 % excreted as part of urine, which is part of the reason it has such a long half life ( between 4-6 hours).

The explanation behind caffeine’s fat burning potential lies in its stimulation of the sympathetic nervous system (SNS). This increases adrenaline levels and in turn helps to liberate fatty acids from adipose (fat) and intramuscular stores making them available for use as fuel.

Caffeine also inhibits the enzyme responsible for degrading cAMP (a derivative of ATP). Higher levels of cAMP enhances lipolysis (breakdown of fat) and thus, like above, creates a larger pool of fatty acids for use as fuel.

Studies have found that even a low dose (100mg) has the potential to induce a thermogenic effect at rest, increasing the resting metabolic rate by 3-4% over a 150 minute period.

Green Tea Extract (catechins)

Green tea extract is, as the name suggests, found in green tea (50-100 mg per 250ml cup). It contains 2 compounds with thermogenic effects: caffeine and epigallocatechin (EGCG).

Research has demonstrated that supplementing with green tea, and in particular with ECGC can increase energy expenditure and stimulate fat oxidation. In a 12 week study of overweight males, for instance, consumption of higher doses of ECGC compared with a lower dose, was associated with far greater reductions in body weight, body fat and visceral fat. The mechanism behind these results is thought to involve the inhibition of an enzyme called catechol-o-methyltransferase, which degrades noradrenaline. By prolonging the action of noradrenaline, overall energy expenditure and fat burning in particular can be increased.

In a separate study featured in the Journal of Nutrition, a 1.7% fat loss experienced by individuals supplementing with catechins in comparison to placebo represented a difference in energy balance of 60 kcals a day. This degree of change was considered clinically important, particularly over a long period of time and in subjects suffering from obesity.


Capsaicin is the compound that is responsible for the pungency of capsicums (spiciness in other words). It has been shown to increase thermogenesis by enhancing catecholamine (i.e. adrenaline) secretion and is also capable of suppressing appetite. A pretty effective double whammy when it comes to losing weight and burning fat.

A review of 20 scientific studies concluded that capsaicin supplements can boost metabolism by up to 50 kcals a day which could lead to significant weight loss over time. Taking 2.5 mg with each meal resulted in 10% more fat being burned in the subsequent 24 hours than a control group. The suspected mechanism for this effect is based on capsaicin’s likely stimulation of  beta adrenergic agonists, which play a role in the SNS.


Yohimbine is an alkaloid obtained from the bark of the yohimbe tree found in Africa and is often taken as a supplement to boost thermogenesis. It increases the activity of several important hormones including, adrenaline, noradrenaline and dopamine and is thought to boost metabolism as a result.

A 3 week study using soccer players demonstrated that a 20 mg yohimbine supplement taken every day, significantly reduced body fat and fat mass in comparison to a control group. Those exposed to the supplement experience an average increase in body mass of 1.2kg but a reduction in fat mass of 2%, equating to an increase in lean muscle mass of 2.5%.

Grains of Paradise

Grains of paradise (Aframomum melegueta), are a species of the ginger family, containing pungent, aromatic ketones such as 6-paradol, 6-gingerol and 6-shogaol. These properties are believed to activate thermogenesis within brown adipose (fat) tissue and thus contribute to energy expenditure and body composition. In fact, a study in human subjects involving daily consumption of Grains of Paradise extract for 4 weeks resulted in a slight but significant

reduction in visceral fat.

Thermogenic combos

The idea behind these is that by combining many of the active ingredients we’ve already discussed into one supplement, they work together in order to generate an even more significant thermogenic response.

There are indeed several studies to show that such blends are capable of increasing metabolic rate. This translates into a resting energy expenditure increase of 6-29% and a 15% boost in oxygen consumption.

Two compounds which have been shown to work especially well together are caffeine and green tea catechins. Studies have shown that supplementation with a thermogenic blend containing both active ingredients resulted in a 10.5% increase in energy expenditure whilst supplementing solely with caffeine induced only a 6% increase. This is because catechins enhance the effect of caffeine by slowing the breakdown of adrenaline by inhibiting the enzyme responsible for its degradation.

Key takeaways

So, if you’re interested in dipping your toe into the thermogenic supplement market, then caffeine is definitely the best place to start. It is categorically the most effective of all the ingredients we’ve discussed here and of any others out there on the world wide web. Study after study has demonstrated that it is capable of boosting your metabolism and helping you to burn more fat. What’s more, it also has some pretty nifty performance enhancing effects for good measure.

If you’re going to experiment with a thermogenic fat burner blend, then our advice would be to check all the active ingredients carefully and do some research. Particularly complementary combinations to look out for are caffeine and green tea catechins so that would be a very good place to start!

When should you use thermogenic fat burners?

If you’re overweight or obese and looking for a helping hand in shifting some of those excess pounds, then thermogenics are most definitely for you. Hard work remains the key to weight loss success, but there is undoubtedly some benefits to be had from choosing the right supplements.

Thermogenics aren’t just for people who are overweight. If you’re trying to build lean muscle or desperately trying to shift that last layer of belly fat concealing rock solid abs, then fat burners could be the missing ingredient in your workout routine!

How much? Dosage and loading


Studies have reported a thermogenic effect at doses as low as 100 mg, but caffeine can be supplemented at up to 400 mg a day, at which point there is no benefit to a higher dose, only potential side effects.

As we’ve already mentioned, it takes between 30 and 90 minutes for caffeine to reach optimum levels in your blood so you’re going to want to take your supplement 30-60 minutes before your workout for maximum benefit.

Green tea extract

There isn’t really a consensus as to an optimum dose of green tea extract so we suggest starting out low and see how you go. A cup a day will certainly be of benefit to your overall health and may help to boost your metabolism. Why not drink it in conjunction with your caffeine supplement pre workout to really get the most out of both!


Doses as low as 2.5 mg three times a day have demonstrated benefits to metabolism so that’s as good a place to start as any.


Again, there isn’t really a consensus as to an optimum dose, but studies have reported positive effects on metabolism whilst taking 20 mg per day. It reaches peak blood concentrations after 30 mins and has a half life of around 5 hours so be sure to take your supplement no longer than 30 minutes before your workout.

Grains of paradise

Studies which have demonstrated the positive effects of Grains of Paradise extract on visceral fat and energy expenditure have involved daily dosage of 30mg for a period of 4 weeks.


The most common side effects of thermogenics include nausea, constipation, abdominal pain and headaches but these tend to occur at very high doses of the respective ingredients. Most people tolerate thermogenic fat burners without any repercussions.

The best thing to do, as with any nutritional supplement, is to test your tolerance with low doses initially before increasing them gradually to achieve optimum effect.