Fat Burners: What They Are, How They Work and Their Risks

There are numerous categories of supplements on the market today, but one in particular stands out as irresistible for those looking to lose weight: fat burners.

These supplements are often marketed as powerful allies for weight loss diets, but aggressive marketing strategies frequently lead to unrealistic expectations.

The reality is that fat burners won’t magically make stubborn fat disappear. However, understanding how they work in our bodies and their level of effectiveness is worth exploring.

In this article, we summarize the scientific perspective on fat burners so you can make an informed decision the next time you’re considering a purchase.

What Are Fat Burners and How Do They Work?

Fat burners, also known as thermogenics, are dietary supplements designed to support weight loss by influencing both sides of the energy balance equation: increasing calorie expenditure and reducing food intake. This is achieved through the following mechanisms:

• Appetite and satiety modulation via neurochemical effects.
• Increased lipolysis—or fat burning—by prioritizing the oxidation of fatty acids, and reduced lipogenesis, which decreases triglyceride accumulation (through the stimulation of the sympathetic nervous system) (1).

These effects, in theory, increase total energy expenditure and help achieve a calorie deficit, potentially leading to a reduction in body fat and overall weight.

Looking to reach your goals faster? 👉 Check out: Calorie Deficit: What It Is and How to Achieve It!

TL;DR (too long; didn't read):

Fat burners, or thermogenics, are marketed to boost calorie burn and reduce appetite, often combining ingredients like caffeine, capsaicin, and green tea extract. However, scientific evidence shows their impact on fat loss and body weight is minimal or clinically insignificant. Even popular compounds like L-carnitine have limited effectiveness unless in specific medical cases. These supplements can also pose health risks, as some products may lack promised ingredients or include banned substances. It’s best to save your money and prioritize a balanced diet and regular exercise instead.

Are Fat Burners Effective?

Keep in mind that fat burners typically don’t rely on a single ingredient. Instead, they use a combination of various components, each with a unique effect on the body.

Some of these ingredients stand out more than others. Let’s dive into the most common compounds found in fat burners and their real impact on weight loss.

Caffeine

Caffeine is a naturally occurring stimulant found in various plants, but it’s most famously sourced from coffee beans.

As a stimulant, caffeine reduces fatigue, enhances cognitive function, increases neurotransmitter release to boost alertness, and minimizes pain, making physical effort feel less demanding while improving muscle activation (2).

It also enhances sports performance, particularly muscular endurance (3), and to a lesser degree, strength (4).

Caffeine is often included in fat burner formulas for its supposed appetite-suppressing properties. However, scientific evidence supporting this claim is limited.

For instance, Panek-Shirley et al.  (5) conducted a study administering 1 mg/kg and 3 mg/kg doses of caffeine, as well as a placebo, to participants before a buffet breakfast to assess if caffeine intake would reduce calorie consumption. Researchers monitored their total caloric intake throughout the day.

Results indicated that participants who consumed 1 mg/kg of caffeine ate roughly 10% fewer calories at breakfast. Yet, this effect was short-lived, as there were no significant differences in overall caloric intake over the entire day. This suggests that caffeine’s appetite-suppressing effect, if present, is minimal and brief.

Additionally, some evidence does hint at caffeine’s role in weight reduction. Tabrizi et al. (6), conducted a meta-analysis suggesting caffeine may contribute to lowering weight, body fat, and BMI.

However, upon closer examination, only 3 out of 13 studies in the meta-analysis analyzed caffeine’s effects alone. The majority investigated multi-ingredient supplements, some of which included ephedrine, a substance banned in several countries. The high variability among studies also undermines the reliability of these findings—a limitation acknowledged by the researchers.

Capsaicin and capsiate

Capsaicin and capsiate belong to the capsaicinoid family, compounds that give chili peppers their spicy kick. While capsaicin causes a strong burning sensation, capsiate is structurally similar but lacks the heat.

Aside from this flavor difference, both compounds have shown potential to enhance muscular endurance, akin to the effects of caffeine (7). However, more research is needed to substantiate their effectiveness compared to other supplements on the market.

Preliminary studies have also highlighted the acute thermogenic and appetite-suppressing effects of capsaicin and capsiate, linking their consumption to reduced body fat and weight. As a result, they’re often included in fat burner formulas or taken separately for these benefits (8).

That said, more recent research has not been able to confirm their effectiveness for weight loss. The latest evidence points to minimal impact on body mass and insignificant long-term fat reduction (9).

Green Tea and Green Tea Extract

Green tea, made from the leaves of Camellia sinensis, is one of the most popular beverages in the Western world. It contains compounds like catechins, caffeine, theanine, and polysaccharides, which have been associated with antioxidant, anti-tumor, and anti-diabetic benefits. Additionally, there’s evidence that its catechins may help prevent conditions such as diabetes, infections, cancer, and skin inflammation (10).

Beyond these health benefits, earlier studies suggested that green tea consumption could have a small yet positive effect on weight loss and weight maintenance. This is mainly attributed to the action of catechins or a combination of epigallocatechin gallate (EGCG) and caffeine found in green tea (11). As a result, green tea or its extract is often promoted as a potential fat burner.

However, later research (including a meta-analysis evaluating the effectiveness of capsaicin and capsiate) has shown that the long-term effects of green tea and its extracts on body fat percentage and waist circumference are not statistically significant or are so minor that they lack clinical relevance (9,12).

L-Carnitine

L-carnitine is a compound naturally found in the body, playing a key role in fat metabolism. Its popularity as a fat loss supplement stems from its involvement in the oxidation of fatty acids to generate energy. This has led to the belief that supplementing with carnitine could boost fat burning and accelerate weight loss.

However, recent research does not support this theory. A meta-analysis by Askarpour et al. (13) concluded that L-carnitine supplementation does not have a significant effect on fat loss, especially in individuals without a deficiency. Therefore, increasing its intake does not appear to have a meaningful impact on body fat percentage or weight loss.

It’s worth noting that some studies in the literature have shown favorable effects on fat loss with L-carnitine supplementation. However, these results are often observed in older populations suffering from sarcopenia or in individuals with specific medical or genetic conditions affecting metabolism (14). These cases do not translate to the same benefits for healthy individuals without an L-carnitine deficiency.

What Does Science Reveal About the Effectiveness of Fat Burners?

As we've seen, fat burners consist of various ingredients, each offering potential health and performance benefits. However, none of them have strong evidence to support a direct and lasting impact on fat loss or body weight reduction.

If doubts remain about the limited effectiveness of fat burners, one need only look at the meta-analysis by Clark and Welch (1).  The authors reviewed 21 studies published between 1998 and 2018, which examined the effects of these supplements on body mass, fat mass, lean mass, total cholesterol, high and low-density lipoproteins, and resting metabolic rate.

The meta-analysis found no clear benefit from using fat burners, proving them less effective than exercise alone or a combination of diet and exercise without supplements. Furthermore, some included studies that lasted over a year utilized ephedrine and prescription medications for obesity, such as phentermine and topiramate. This indicates that even with the most potent products, the results weren’t significant enough to claim that fat burners have a substantial effect on weight loss.

Are Fat Burners Risky to Take?

You might already be convinced that fat burners aren't the best solution for actually burning fat. However, if you choose to use them for any reason—despite our recommendation not to spend your money on them—make sure the supplement comes from a reputable company and, ideally, has been third-party tested to certify its quality and safety.

If not, you could be putting your health at risk. In the United States, a study analyzed various sports supplements sold in stores, including fat burners. The findings revealed that 40% of the tested supplements did not contain a significant amount of the main compound they claimed to have.

Additionally, 12% of these products contained ingredients banned by the U.S. Food and Drug Administration (FDA), such as synthetic stimulants (1,4-dimethylamylamine, deteranol, octodrine, and oxilofrine) and omberacetam, a nootropic drug (15).

It’s also worth noting that products containing ephedrine were sold for years as fat loss aids until the FDA banned them in 2004 after being linked to the deaths of several athletes  (16). As new compounds with supposed weight loss benefits emerge, it’s wise to wait for proof of their safety before trying them to avoid repeating past mistakes.

In Summary...

Fat burners, or thermogenics, are marketed as supplements that increase calorie expenditure and suppress appetite to aid weight loss. These products often combine ingredients like caffeine, capsaicin, and green tea extract. However, their effectiveness is debatable, as the strongest scientific evidence indicates that their impact on fat loss and body weight is minimal or clinically insignificant. Even popular compounds like L-carnitine have not proven effective, except in specific cases involving certain medical conditions.

Moreover, fat burners come with risks. Some products have been found to lack the promised amounts of active ingredients or even contain banned substances. Therefore, if you do choose to use them, ensure that the supplement is from a trusted brand and has undergone third-party testing to guarantee its quality and safety.

In conclusion, given the limited impact of these supplements, it’s best to save your money and focus on more effective methods, like a balanced diet and regular exercise.