The Definitive Guide to Fat Burner Supplements | Legion

With the weight loss market valued at a staggering $60.5 billion and more than one-third of U.S. adults obese, it’s no surprise that there’s a glut of “fat burners” for sale these days.

And for the same reasons it’s also no surprise that fat burners are some of the most expensive supplements on the shelves and feature some of the loudest marketing claims, often making big promises of “scientifically proven” rapid fat loss.

How well do these products actually work, though? Enough to warrant the significant expense?

Let’s find out.

Why the “Fat Burner” is Fundamentally Misleading

One of the reasons fat burners sell so well is the moniker itself: When you’re trying to lose fat as efficiently as possible, then a “fat burner” just sounds like a perfect addition to your regimen. Anything that “burns fat” is worth a go, no?

It’s not that simple, though. No natural substance can just “burn fat” outright, regardless of how complex or pseudo-scientific the explanations are.

You see, in order to sell you on their fat burners, supplement companies will often talk about increasing fat oxidation rates, preserving lean mass, supporting the thyroid, inducing thermogenesis, inhibiting enzymes related to fat storage, inducing enzymes that cause fat loss, manipulating hormone and neurotransmitter levels, reducing water retention, improving nutrient partitioning, and more.

Well, the truth is, these are all aspects of fat loss, but this type of marketing is little more than an attempt to dazzle you with terminology and scientific half-truths in hopes that you just accept the claimed benefits at face value.

When you take a cold, hard look at the science of fat loss, there are really only three ways to appreciably speed it up:

You can speed up your basal metabolic rate.

Your metabolic rate is a “count” of how much energy your body burns throughout the day, and the higher it goes, the faster you can lose weight.

This is because when you boil fat loss down to its utmost simplicity, it’s determined by something known as your body’s energy balance, which is the difference between the energy your body burns and the energy you feed it with food. Expend more energy than you consume over time, and you’ll lose fat.

While there are many, many ways to increase metabolic rate, they ultimately rely on one or both of the following mechanisms:

1. Encourage a cell to produce more energy from carbohydrates and fatty acids.
2. Reduce efficiency of the process through which cellular energy is produced, thus increasing the “energy cost” of meeting the body’s needs.

There are ways to manipulate those mechanisms through supplementation, and we’ll get to them in a minute, but they’re not as numerous or powerful as some supplement companies would have you believe.

 You can prevent hunger or cravings from ruining your plans.

A major reason even good diets fail is people just aren’t able to stick to them long enough. Wishes turn into cravings and ultimately binges, which can undo days or even weeks of hard work if it really gets out of hand.

While some people have an easier time than others, almost everyone has to deal with hunger and cravings to one degree or another. It’s just human nature to want to indulge in food after accidental or intentional deprivation, and regardless of whether it’s normal, it’s still interfering with your goals.

Some natural compounds are known to reduce hunger and others are known to increase the sensation of fullness you get from a meal, and a combination of proven molecules can be used to successfully reduce hunger and cravings and derive the maximum benefits from your diet.

You can make the overall experience of dieting more enjoyable.

Make no mistake: while changing your body with diet, exercise, and supplementation can dramatically change your life for the better, it’s not easy.

No amount of pills or powders is going to get you there. It takes hard work, and it takes time. And this is another major reason why diets fail: people don’t want to go through the discomfort of it all.

Well, like reducing hunger and cravings, making the process of dieting more enjoyable, primarily by increasing the overall feeling of well-being, makes it easy to stick to the plan and see it through.

This can be achieved in various ways, but the three most effective are:

1. Utilizing a modest calorie deficit: If you eat too little every day, you’ll lose weight but your body is not going to feel good. Furthermore, you can also lose quite a bit of muscle
2. Eating foods you like: Fat loss doesn’t require abstaining from any type of food. Yes, you should get the majority of your daily calories from nutritious foods, but that gives you a lot to choose from. Unless you’re a junk food addict, pretty much anything you’d actually want to eat every day can and should be worked into your meal plan.
3. Supplementing smartly: As you’ll soon see, supplementation can help with overall satiety and well-being, which makes it even easier to stick to your diet.

What Makes a Good “Fat Burner”?

Although the physiological machinery involved in fat loss is vast and complex, the practical application remains simple.

Contrary to what many supplement companies would lead you to believe, directly stimulating any of the thousands of proteins and enzymes involved in fat loss either doesn’t work or is uninvestigated.

Fat loss is a whole-body process, and for a fat burner to be truly based on good science and noticeably affect fat loss results, it should focus on simple, key, and proven targets because then everything else activates and functions accordingly.

Thus, a good “fat burner” would increase our basal metabolic rate, would reduce hunger and cravings, and would increase satiety and feelings of overall well-being.

Let’s look at some natural molecules often found in fat burners that can and can’t get the job done.

Caffeine

Caffeine helps you lose fat by simply increasing your body’s daily energy expenditure.

As weight-loss boils down to energy consumed vs. energy expended, caffeine helps you maintain a calorie deficit.

Caffeine has other benefits for us fitness folk, though. It improves strength, muscle endurance, and anaerobic performance, and also reverses the “morning weakness” experienced by many weightlifters.

The Bottom Line

Caffeine is a well-tolerated and effective fat loss aid and should be included in or with a good fat burner supplement.

Raspberry Ketones

Raspberry ketones are the primary aroma compound of the red raspberry (it gives the raspberry its smell), and it’s also found in other fruits like the blackberry and cranberry.

How did such a seemingly random compound find its way into weight loss products?

Well, it started with a couple animal studies. One demonstrated that raspberry ketone supplementation prevented weight gain by increasing lipolysis and fat oxidation, and the other backed up this mechanism.

That might be promising if it weren’t for a few little details:

• Animal research can not be used as proof of human effectiveness. The human and rat body just isn’t similar enough, and this is especially true when talking about metabolic functions.
• One of the rat studies was in vitro research. This means parts of living rats were removed to be studied in isolation, as opposed to research done with living, intact organisms (in vivo research). In vitro research is less definitive than in vivo because living organisms are incredibly complex, and sometimes in vitro findings just don’t pan out in vivo.
• The in vivo rat study that demonstrated weight gain prevention used an absolutely massive oral dose: up to 20 g/kg of body weight, or 4761 times greater than the average human intake.

There is one human trial I know of that is commonly cited as evidence of raspberry ketone’s effectiveness for weight loss.

The problem with this study, however, is the compound was paired with caffeine, capsaicin, garlic, ginger, and citrus aurantium as a source of synephrine. It’s impossible to know if the raspberry ketone did anything or not.

The Bottom Line

There is insufficient evidence to support the use of low oral doses of raspberry ketone for fat loss purposes. It has no place in a fat burner supplement.

Synephrine

Synephrine is a chemical compound found in certain types of citrus fruits (particularly the bitter variety).

It’s chemically similar to ephedrine and catecholamines (the chemicals adrenaline and noradrenaline, which cause the breakdown of fat cells), and although less potent than those two, it induces similar effects.

Research shows that supplementation with synephrine:

• Increases both basal metabolic rate and lipolysis
• Inhibits the activity of certain types of fat cell receptors that prevent fat mobilization
• Increases the thermic effect of food, which is the “energy cost” of metabolizing food

Furthermore, research shows that synephrine works synergistically with caffeine to enhance both caffeine’s and its own fat loss properties. The synergism noted in a standard “ECA” (ephedrine, caffeine, and aspirin) stack also applies to synephrine.

Additionally, anything that has the ability to increase catecholamine activity can also suppress hunger between meals (a component of the fight or flight response), and thus synephrine is generally considered to be an appetite suppressant.

The Bottom Line

Synephrine is a safe, proven fat loss aid that should be included in a fat burner supplement.

Garcinia Cambogia

Garcinia cambogia is a small fruit often used in Indian and Asian cuisine to impart a sour flavor.

It’s a good natural source of hydroxycitric acid, and has received a lot of media attention recently as a weight loss aid.

These claims are unfounded, however.

Like many fad supplements, garcinia cambogia has some animal research on its side, but human research is contradictory and hard to interpret.

A couple rat studies have demonstrated that garcinia cambogia can reduce weight gain during a period of overfeeding. The mechanism by which it accomplished this is the suppression of fatty acid synthesis in the liver (it reduced the amount of fat the body could make from the excess calories).

Human research bursts that bubble, though.

A meta analysis of 12 randomized clinical trials of garcinia cambogia found the following:

• Three studies with small sample sizes reported statistically significant, albeit small, decreases in fat mass over the placebo groups. (In case you were wondering, the best result was 1.3 kg more weight lost than the placebo group over a 3-month period.)
• Two studies found no difference in weight loss between the garcinia cambogia and placebo groups, including the largest and most rigorous study reviewed.
• The results of the remaining studies reviewed were marred by serious design and/or execution flaws.

The Bottom Line

Current research says that, despite its current popularity, garcinia cambogia probably won’t help you lose weight and thus isn’t worth including in a fat burner supplement.

Green tea extract is a herbal product derived from green tea leaves. It contains a large amount of a substance known as a “catechin,” which is responsible for many of tea’s health benefits.

One of these benefits relates to weight loss: research has shown that supplementation with green tea extract reduces total fat mass, accelerates exercise-induced fat loss, and can help reduce abdominal fat, in particular.

The primary mechanism by which it accomplishes this is inhibiting an enzyme that degrades catecholamines, which are chemicals that mobilize fat stores to be burned for energy.

This also makes green tea extract work synergistically with caffeine—caffeine increases catecholamine levels, and green tea extract extends the amount of time they spend in the blood.

The Bottom Line

Green tea extract is an effective fat loss agent as well as an effective weight management agent and can be used in a fat burner supplement to directly help with fat loss and amplify the effectiveness of caffeine and synephrine.

Green coffee extract is a supplement derived from green coffee beans. It’s similar to regular coffee beans, but has high amounts of a substance known as chlorogenic acid.

This substance is particularly hot at the moment, thanks to people like Dr. Oz and other mainstream “health gurus.” It may not be everything they claim, though.

A recent meta-analysis of the 5 human trials available found that high dosages of chlorogenic acid via green coffee extract (400-to-800 mg chlorogenic acid per day) may induce fat loss, but researchers noted that the studies demonstrating this had high risks of bias due to funding sources (for-profit companies producing green coffee extract).

The Bottom Line

Green coffee extract may help you lose weight if taken in high enough dosages. However, until more research is done on it, and particularly unbiased research, green coffee extract’s value as a fat loss supplement is uncertain. 

Thus, I don’t believe it’s worth including in a fat burner over other proven ingredients.

Carnitine

Carnitine is a compound that your body produces from the amino acids lysine and methionine, and it plays a vital role in the generation of cellular energy.

While there is scientific evidence that carnitine supplementation can help with muscle recovery after exercise, does it have anything to offer in the way of weight loss?

Well, it does have a mechanism that is of interest: it increases fat oxidation in the muscles.

What this means is it appears to increase the rate at which muscle tissue burns fat for fuel instead of glycogen. Theoretically, this might result in additional fat loss while exercising.

Actual research is less than promising, however.

There’s evidence that carnitine can reduce fat mass and increase muscle mass in the elderly, but these effects were not seen when it was tested with overweight pre-menopausal women. Animal research has also failed to demonstrate any weight loss benefits when simply combined with a calorie-restricted diet.

Thus, scientists don’t know yet if carnitine’s metabolic effects are profound enough to actually accelerate weight loss when combined with exercise. Animal research says no, as well as a human trial (which isn’t definitive due to flaws in design, but is worth noting).

The Bottom Line

Unless your body’s ability to oxidize fat is impaired by disease or dysfunction, the research currently available says that carnitine supplementation isn’t likely to help with weight loss. There’s no reason to include carnitine in a fat burner supplement.

5-HTP

5-HTP is a compound involved in the metabolism of the amino acid tryptophan, which is found in foods like milk, meat, potatoes, pumpkin, and various greens. It’s converted into serotonin in the brain, which is one of the principal neurotransmitters involved in feelings of happiness.

5-HTP is used over L-tryptophan as it can cross the blood-brain barrier (whereas L-tryptophan can’t), and used preferentially over serotonin itself due to a greater safety profile with oral administration.

Research shows that, when taken with food, 5-HTP increases feelings of fullness and thus helps you control your food intake. Furthermore, studies have demonstrated that 5-HTP’s satiety mechanism can reduce cravings for carbohydrates in particular.

The Bottom Line

For most people, the toughest part of dieting is just sticking to it. Anything that naturally and safely helps reduce the desire to overeat is worthwhile, and that’s why I like to see 5-HTP in a fat burner supplement.

Forskolin

Forskolin is found in the Indian herb Coleus forskohlii and has long been used in Ayurvedic medicine to treat heart and respiratory disorders.

Supplementation with forskolin increases blood plasma and intracellular levels of a molecule known as cyclic adenosine monophosphate (cAMP), which functions as an intracellular “message relayer” vital to various biochemical processes including the regulation of glycogen, sugar, and lipid metabolism.

cAMP and ATP—adenosine triphosphate, the most basic form of cellular energy in the body—interact in a very simple yet powerful way in the cell. 

When ATP is high it indicates a plentiful energy state and the body will aim to store and build tissue, but when cAMP is high it signifies a lack of ATP and thus initiates a process to make more ATP by burning through energy reserves.

Forskolin activates an enzyme known as adenyl cyclase, which converts ATP to cAMP, thereby greatly increasing the ratio in favor of cAMP and initiating the energy-burning process. Furthermore, forskolin’s effects are amplified by the effects of synephrine.

This isn’t just abstract theory, either: research shows that supplementation with forskolin accelerates fat loss and increases testosterone levels.

The Bottom Line

Forskolin can accelerate fat loss through proven, well-understood mechanisms and is a worthwhile inclusion in a fat burner supplement.

Yohimbine

Yohimbine is a substance found in the Pausinystalia yohimbe plant, and helps block a mechanism in fat cells that prevents weight loss, which in turn speeds up fat loss.

There’s a catch, though: You must be in a fasted state for it to work (check out this article on fasted training for more information on this). The insulin spike that occurs after eating a meal completely negates the beneficial effects of yohimbine.

As with anything, excess doses of yohimbine can have negative side effects, so only use supplements containing it that  use a clinically effective and safe dose. Furthermore, yohimbine has been shown to raise blood pressure. If you have high blood pressure, I don’t recommend you use it.

The Bottom Line

Yohimbine is an effective fat loss accelerator, but you should only take supplements that contain a safe and effective dose. 

Black Ginger

Black ginger, also known as Kaempferia parviflora, is an herb native to Thailand that has traditionally been used to improve virility and physical performance and support weight management.

It contains several active compounds known as methoxyflavones, which appear to boost fat burning by increasing energy expenditure through uncoupling, a process where fat cells release energy as heat instead of storing it.

What’s more, studies show it also decreases fat storage by activating PPARγ, a receptor that helps regulate fat accumulation and metabolism.

The Bottom Line

Black ginger increases fat burning in several ways, making it a valuable addition to a fat burner supplement.

Grains of Paradise

Grains of Paradise is the common name for the plant Aframomum melegueta, which is a herb in the ginger family that’s commonly used as a spice.

It contains various compounds like 6-gingerol and 6-paradol that can increase metabolic rate by influencing receptors on fat cells involved in energy regulation and perception of temperature.

That’s why research shows that supplementation with Grains of Paradise increases energy expenditure (to the tune of about 100 calories) and reduces visceral fat levels.

The Bottom Line

Grains of Paradise is a research-backed ingredient that increases calorie burning and may help reduce belly fat, making it a useful addition to a fat burner supplement.

Fucoxanthin

Fucoxanthin is a vitamin A-like molecule known as a carotenoid that’s found in seaweed.

Like black ginger, it enters fat cells and increases energy expenditure through uncoupling, which helps accelerate weight loss.

Additionally, studies show that it can also hinder fat storage by inhibiting the absorption of glucose into fat cells and augmenting its uptake into muscle cells.

The Bottom Line

Fucoxanthin is a promising fat loss aid worth including in a fat burner supplement because it increases fat burning and helps prevent fat storage.

Caralluma Fimbriata

Caralluma fimbriata is an edible cactus found primarily in India that has long been used to suppress appetite when food is scarce.

Scientists are still investigating how it works, but research shows that supplementation with Caralluma fimbriata reduces appetite as well as stress and cortisol levels, which can further decrease the desire to overeat.

The Bottom Line

If you find controlling your appetite challenging, Caralluma fimbriata could make a real difference. By naturally reducing hunger and stress-related cravings, it helps you stay on track without white-knuckling every meal.

Hoodia

Hoodia gordonii is a succulent plant from southern Africa, long used by indigenous tribes to suppress hunger. This traditional use led to its rise as a popular weight-loss supplement, with claims that it reduces appetite and helps people eat fewer calories.

However, research suggests otherwise. The only human study on hoodia found it was no more effective than a placebo at controlling hunger or aiding fat loss. Worse, it caused several negative side effects, including increased heart rate, elevated blood pressure, nausea, and dizziness.

The Bottom Line

With no proven fat-loss benefits and potential health risks, it’s best to avoid hoodia and focus on well-researched supplements that actually boost fat burning.

Apple Cider Vinegar

Apple cider vinegar has been a popular health tonic for centuries, often touted for its ability to aid weight loss, regulate blood sugar, and improve cholesterol levels. This has led to the rise of apple cider vinegar supplements, particularly in gummy form, as a convenient alternative to drinking the vinegar itself.

However, while some research suggests apple cider vinegar may slow digestion and modestly curb appetite, there’s little high-quality evidence that it significantly impacts weight loss. 

Studies on blood sugar control and cholesterol levels are also mixed—some suggest mild benefits, but most are small, short-term, or biased.

The Bottom Line

Apple cider vinegar is more hype than help when it comes to weight loss and overall health. If you’re looking for an effective fat burner supplement that’s backed by a lot of high-quality research, there are far better choices.

Conjugated Linoleic Acid (CLA)

CLA is one of the most popular fat-loss supplements on the market, but its reputation isn’t backed by strong evidence.

While research on animals shows CLA can significantly boost fat burning and prevent fat gain, studies in humans paint a different picture. Most show CLA has little to no effect on fat loss, and the few that report benefits are underwhelming.

For example, some studies found that supplementing with CLA for 12 weeks led to just ~1-to-2 pounds of additional fat loss—hardly game-changing results. Other research suggests CLA’s effects are unpredictable, with some people losing fat, others gaining fat, and some seeing no change at all.

What’s more, CLA doesn’t seem to suppress appetite or prevent weight regain after dieting, making it even less useful as a fat-loss aid.

The Bottom Line

CLA isn’t an effective fat burner. While some research suggests it may offer a small fat-loss benefit, the effects are weak, inconsistent, and unreliable. There are far better supplements for fat loss.

The Best Fat Burner Supplements

While the above list of molecules doesn’t cover everything you’ll find in popular fat burners, it covers the most common ones. And if you start looking at the ingredients lists of various products on the market, you’ll quickly notice a couple things:

1. Many fat burners contain ingredients like raspberry ketones and garcinia cambogia that have been scientifically proven to be ineffective.
2. Most fat burners don’t contain many of the ingredients listed above scientifically proven to be effective, and those that do almost always use tiny dosages that simply won’t deliver the same results seen in clinical studies.
3. Almost all fat burners contain a long list of ingredients that have no research whatsoever related to fat loss.

The sad truth is the majority of fat burners on the market contain little more than a handful of cheap stimulants to make you feel like you’re burning fat and a smattering of underdosed, unproven, or ineffective (and often all three!) ingredients thrown in to pad the ingredients list and make you think you’re getting a lot for your money.

While there have been a couple decent fat burners over the years and I’ve used and recommended them, they always fell short of what I really wanted to see in terms of ingredients and dosages.

Thanks to your support of my writing and supplement line, Legion, I’m finally able to just make the fat burners I always wished someone else would make: Phoenix and Forge.

Phoenix Fat Burner

Phoenix is a fat burner designed to support fat loss and energy levels and reduce hunger and cravings, all without the jitters, upset stomach, or crash that come with taking most fat burner supplements. 

It contains clinically effective doses of 8 science-backed ingredients, each proven in peer-reviewed research to support fat loss:

• 200 mg of caffeine
• 100 mg of black ginger
• 30 mg of Grains of Paradise
• 50 mg of forskolin
• 8 mg of fucoxanthin
• 1,000 mg of Caralluma fimbriata
• 150 mg of 5-HTP
• 150 mg of L-DOPA

Phoenix also provides essential nutrients like iodine (240 μg), vitamin B6 (1.7 mg), and vitamin B12 (2.4 μg) to support overall health while dieting and make weight loss as straightforward as possible.

Unlike most fat burners, it contains no harsh stimulants, artificial additives, or unnecessary chemicals like food dyes and sweeteners. And every bottle is tested in an ISO 17025 accredited lab to ensure purity and potency, so you know exactly what you’re putting into your body.

The bottom line is if you want to lose fat faster without pumping yourself full of stimulants or other potentially harmful chemicals, then you want to try Phoenix.

Forge Pre-Workout Fat Burner 

Forge is a pre-workout fat burner designed for fasted training. It helps you lose fat—especially stubborn fat—faster while preserving muscle, maintaining training intensity, and sharpening mental focus.

It contains clinically effective doses of three research-backed ingredients that enhance fat loss and exercise performance while reducing muscle breakdown:

• 10 mg of yohimbine
• 2.5 g of HMB
• 300 mg of synephrine

Like Phoenix, Forge is free from artificial dyes, fillers, and unnecessary chemicals, and every batch is third-party tested to ensure purity and potency.

If you want to maximize fat loss while training fasted—without sacrificing muscle or performance—then you want to try Forge.