Update 9/17/22. Fat burners are some of the most popular supplements around. But, are they safe and do they really work? The advertisements for these supplements make it seem like they are almost miraculous in their weight loss results. But is it really true? I've looked at many of fat burners over the years. Let's look at fat burner marketing buzz words, and ingredients and see what we can discover.
Weight Loss / Fat Burner Reviews
For more insights, see these additional reviews:
See the weight loss page for many other reviews.
Also see: Weight loss supplements with proof
How Do Fat Burners Work?
Metabolism is basically the speed we burn calories. Faster metabolisms burn calories faster than slower metabolic rates. Fat burner supplements are touted to raise your metabolism, causing more calories to be used than you normally would. This in turn, is supposed to help you burn off excess subcutaneous and visceral fat, resulting in weight loss.
Fat burners containing stimulants might also work by making you feel more awake. The more awake and energized you are, the more physical activity – exercise, gardening, housework, etc. – you might perform. All this additional activity can add up to extra calories used, further helping weight loss.
How To Recognize Fat Burners
Fat Burners are pretty easy to recognize if you remember these tips. Their names often start or contain words such as:
- Thermo
- Lipo
- Phen (or Fen)
- Extreme
- Burn (or other references to heat)
- Shred
- Metabo
- Accelerate (or words sounding like this)
- The name contains the letter “X”
Here's why their names often contain these words/prefixes:
Thermo
The prefix “thermo” is short for thermogenic and thermogenesis. Thermogenic refers to anything that's supposed to raise your metabolic rate.
Lipo
Lipo refers to fat. It also refers to lipolysis which is the scientific word for fat burning. So adding this word to the name subtly tells you the supplement will burn fat.
Phen (or Fen)
Phen is short for phentermine, a weight loss drug that is an amphetamine stimulant. Phen is also a reference to Fen-Phen, a now-banned weight loss drug in the 1990s which was linked to heart damage and pulmonary high blood pressure.
Extreme
Extreme is one of those really good marketing words. When supplements contain the word extreme it's meant to convey the message the product provides hard-core, 0ver-the-top results (it may or may not. Remember, this is marketing).
Burn
This is another marketing word. When the name of a supplement contains “burn,” it's meant to tell you the product will either burn your fat off or raise your metabolic rate. Some supplements which are not technically fat burners may also contain this word.
Shred
Adding this word to the name is a reference that the supplement is supposed to shreds fat from your body.
Metabo
Metabo is short for metabolism. Assume any supplement containing metabo or words making reference to metabolism, is designed to elevate your metabolic rate.
Accelerate
To accelerate means to go faster. Supplements whose names make reference to speeding or acceleration are referring to their abilities to make your metabolism go faster.
The letter “X“
The letter X is short for extreme. Extreme means to be the highest degree or best. Supplement names using X and extreme are trying to convey they are best at what they claim to do. Also, X and extreme are cool-sounding and trendy.
Fat Burner Key Ingredient
Many fat burners provide various vitamins (like B12) and minerals (like chromium picolinate) but these are not the active ingredients. The weight loss proof for vitamins and minerals ranges from zero to sketchy at best.
The key ingredients in fat burner supplements are stimulants, most notably caffeine. On supplement labels, caffeine can also be recognized by names such as trimethylxanthine (tri-methyl-zan-theen) and guarana:
Caffeine's Other Names
| Caffeine anhydrous | Pure caffeine | Theobroma cacao |
| trimethylxanthine | Guarana | Black tea extract |
| Natural caffeine | Kola | White tea extract |
Grapefruit is another ingredient sometimes added to fat burners. Grapefruit seems to slow the breakdown of caffeine. By slowing the clearance of caffeine, grapefruit helps caffeine work longer in the body. Grapefruit can also interfere with various medications too.
In addition to grapefruit, some supplements also contain black pepper. Why? Black pepper improves the absorption of many other ingredients. On labels, it may be identified as either black pepper or:
- Piper nigrum
- BioPerine
Stimulants In Fat Burners
Most fat burners contain stimulants. While caffeine is often the key ingredient, supplement companies usually combined it with other stimulants such as:
- Higenamine
- Hordenine
- Synephrine (AKA bitter orange /citrus Aurantium)
- Methylsynepherine
- PEA (Phenylethylamine)
By adding several stimulants together, it's hoped they act together to produce a bigger, better effect. Sounds plausible, although most stimulant combinations lack clinical proof they really work as intended.
Other ingredients which may be added to fat burners nclude:
- Tyrosine
- Capsicum
- L-carnitine
- CLA (Conjugated linoleic acid)
Let's take a quick look at the science on these ingredients and make sense of them:
Higenamine
Higenamine is a stimulant. On supplement labels it may be listed as:
- Lotus seed
- Lotus seed extract
- Nelumbo nucifera
- Snakeroot
Higenamine seems to act directly on the heart by making it work harder, so it can pump more blood. This can elevate heart rate. Here's a video I created which summarizes the science on higenamine:
No human studies have looked at higenamine and weight loss. So it's unknown if it works or not. Higenamine is banned by the World Anti-Doping Agency (WADA). This is important for anyone who is drug tested.
Hordenine
Hordenine, a natural substance found in barley and beer has been investigated since the early 1900's. Hordenine is also a substance found in small amounts in bitter orange (citrus aurantium– see below). Hordenine is a stimulant and is sometimes used not only in fat burner/weight loss supplements but pre-workout supplements too.
Technically hordenine is called a sympathomemetic drug. Sympathomemetic (sym-path-O-me-met-ik) means it mimics how drugs act on the sympathetic nervous system. The sympathetic nervous system is the part of your nervous system which tends to speed things up – like metabolism.
One problem is little research has delved into the effects of hordenine on humans. Also, most research (and there's not a lot of that either) has looked at hordenine as part of multi-ingredient supplements. This means we don't know how effective of a fat burner hordenine -by itself – is or what it's side effects might be.
Synephrine
Synephrine is one of the most widely used ingredients in fat burners. It's also called:
- bitter orange
- citrus aurantium
Like hordenine, synephrine is also a sympathomimetic stimulant. When ephedra (also called Ma Huang) was banned in the US, synephrine quickly filled the gap, becoming the main ingredient in “ephedra-free” supplements.
This is because synephrine “looks” like ephedra.”
The idea was if it looked like ephedra, it might work like ephedra.
Basically, synephrine stimulates adrenaline production in the body. This can elevate heart rate and blood pressure. While some say these effects do not occur, I can tell you my heart rate and blood pressure did go up when I experimented with synephrine several years ago.
Methylsynephrine
Methyl-synephrine is a stimulant. It's a substance related to synephrine. It also goes by the names:
- oxilofrine
- p-hydroxyephedrine
Oxilofrine is the name of a drug that was developed to help people with low blood pressure. Oxilofrine, raises blood pressure.
Because in some countries (not the US) methyl-synephrine is used as a drug, the FDA does not consider this substance a dietary supplement.
The FDA has sent warning letters to companies that use methyl synephrine. In spite of this, it's possible some supplements may still contain this ingredient. For example, methyl-synephrine was listed as an ingredient in :
Despite its popularity in, no proof of weight loss effects can be located. Like higeamine, methylsynephrine is a banned substance by the World Anti-Doping Agency (WADA).
PEA
Phenethylamine (PEA) is a stimulant. Chemically, PEA, looks like amphetamines. Because it has mood altering properties, its use in supplements may be in the hope it helps elevate mood and depression. The idea is if you're not depressed, you don't eat as much.
PEA was listed as an ingredient in the following supplements:
- Thrive W (review)
- 1 DB Goddess (review)
- Nano Go (review)
- Plexus Slim Accelerator (review)
Popularity aside, no proof PEA burns fat or helps people lose weight can be located.
Tyrosine
Tyrosine is an amino acid. One of the things tyrosine does is help us make chemicals called neuro-transmitters such as L-DOPA (a mood chemical) and epinephrine (adrenaline). Companies may add tyrosine to supplements to:
- improve mood
- improve adrenaline production
Tyrosine does seem to improve some aspects of memory and mood. But, as for improving exercise performance, weight loss or burning fat due to elevated adrenaline production, evidence is lacking.
Capsicum
Capsicum may be recognized on supplement labels but its other names:
- Cayenne
- Chili pepper
Cayenne is a spice. The active ingredients are called capsaicinoids. When we eat spicy foods, our metabolism tends to go up. There is some evidence cayenne can help weight loss.
Researchers in the UK, noted capsicum appears to result in an extra 50 calories burned per day. This could cause significant weight loss after 1-2 years.
How does cayenne work? Eating chili peppers (or taking a supplement) before meals, seems to reduce food intake. Another way researchers speculate cayenne might work is by altering our hunger preferences so we more carbs and less fat.
If we remember every gram of carbs has 4 calories while every gram of fat has 9 calories, switching to carbs over fat, could – in theory -result in fewer calories eaten.
Cayenne / capsicum is an interesting compound but by itself, I don't think it will cause much weight loss.
L Carnitine
Carnitine is basically a taxi-cab molecule. It transports fats to the mitochondria where they can be burned for fuel. So, the idea is, the more carnitine you have, the more fat you burn? Sounds pleasurable but does it work?
I don't think anyone can say for sure.
Some studies show carnitine works while other researchers find it doesn't work. Complicating matters is evidence showing L-carnitine supplementation might actually increases body weight in people with cancer.
Conjugated Linoleic Acid
Conjugated linoleic acid (CLA) may be found as an ingredient in fat burners or you may use it by itself as a standalone product. Over the years, various studies have linked CLA to reduced body weight. Like many supplements, not all research supports this but there are enough studies to make me think it may help some people.
The weight loss is not a lot though. Maybe just a few pounds.
The role of CLA and diabetes risk is controversial. On one hand, CLA seems to reduce insulin resistance (Pre-diabetes). On the other hand, CLA might raise the risk by increasing insulin levels (hyper-insulinemia).
CLA is not a single molecule. There are several different types. The version of CLA which might increase diabetes risk is called “trans-10,cis-12.”
CLA supplement labels do not tell us which versions of CLA they contain. Most supplements are a mixture of different types. Not all studies show CLA increases diabetes risk so how common this might be is not known.
Since muscle uses sugar for energy, could building muscle with exercise help defend against CLA-induced diabetes? In theory, it might but this is speculation until the studies are done.
Did I miss any fat burners? Let me know in the comments below.
It’s so funny I should see this now. When I was at GNC looking for a fat burner, the salesperson said the same thing you did – caffeine was the active ingredient in all of them. Maybe the universe is trying to tell me something?
Hi Anne, its so funny you bring this up. Because when I was at a health food store doing research for this fat burner review, the person working there said the exact same thing to me too! I’m glad they are honest about it 🙂