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ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, Fat Burners: What Science Says About Effectiveness & Safety

Fat Burners: What Science Says About Effectiveness & Safety

Reading Time: 5 minutes 40 seconds


DATE: 2022-09-02

Your client’s primary goal is weight loss. However, they’re not seeing results as fast as they’d like. So, they tell you that they want to try (or have already started using) a fat burner. But they’d like to know what you think.

Keeping in mind your scope of practice, you can help clients understand what science says about fat burner effectiveness and safety. First, let’s talk about how fat burners work. We’ll also discuss some of the most common ingredients for increasing fat loss.

How Fat Burners Work

A lot of fat burners work by increasing metabolism. These are known as thermogenic fat burners. Creating a calorie deficit is required for weight loss. The more metabolism goes up, the more calories you burn.

Increased metabolism also means that you have more energy. This makes it easier to stick to your exercise plan. The more you exercise, the greater your ability to burn body fat.

Some fat burners include other ingredients that aid in weight loss, though in different ways. For instance, some include appetite suppressants. When you aren’t fighting food cravings, it’s easier to make healthier choices. It’s also easier to limit portion sizes. So, while they don’t burn fat, they do keep you from adding to your caloric intake and potentially adding to your fat stores.

Others might include an ingredient that claims to reduce fat absorption. The less fat your body absorbs, the greater your ability to control your body weight, even if your diet is less than perfect.

Common Fat Burning Ingredients

Fat burners can be a lot of different things. Although, there are few ingredients found in many of these products.


Carnitine plays a key role in the mobilization of body fat for fuel. It is for this reason that it has become popular as a fat burning supplement. The theory is that the more carnitine you can ingest, the more fat your body will burn. Athletes like it because a greater dependency on fat for fuel would spare precious carbohydrates, increasing aerobic endurance. 


Caffeine is a drug used all over the world, usually for its stimulant effects. It increases alertness, lowers the perceived exertion of exercise, and decreases reaction time. Caffeine is also known as a fat burner. It works by increasing the rate of fatty acid metabolism. It also decreases the rate of carbohydrate (glucose) metabolism during aerobic exercise. 

Green Tea Extract

Green tea also has caffeine, though less than coffee. That makes it preferable to people who are sensitive to this ingredient. It’s also preferred by those interested in natural fat burners since green tea comes from the Camellia sinensis plant. Not to mention, it’s an easy ingredient to consume. You can find green tea drinks in almost any convenience store.

Protein Powder

Protein is known for increasing metabolism. That’s why you have more energy after a high-protein meal. This fat burning nutrient also suppresses your appetite. It fills you up, so you feel fuller longer. This makes weight loss easier because you’re not always battling your hunger.

What Science Says About Fat Burner Effectiveness

A 2021 review in Nutrition and Health looked at 21 studies involving a weight loss supplement. It found that a thermogenic fat burner may provide limited benefits. However, a supplement was less effective than exercise alone or diet combined with exercise.

Some research has looked at the effectiveness of individual ingredients. One review found that people who took carnitine lost more weight than those who didn’t take this supplement. They also had a greater decrease in body mass index. Though, the magnitude of weight loss decreased significantly over time. This suggests that carnitine may provide better results in the short versus long-term.

Another study involved subjects consuming caffeine pre workout. After two weeks, the group receiving caffeine had a greater decrease in body fat. Yet, there was no difference in energy expenditure at rest or during exercise. Instead, caffeine appeared to increase energy post workout.

Studies involving green tea extract have also shown positive results. One involved overweight female participants. Those receiving green tea extract had greater weight loss. They also had more improved body fat percentages. Some research even connects green tea with greater belly fat loss, specifically.

What about protein for fat loss? One review reports that higher protein intake helps athletes achieve weight loss without losing muscle mass. It also provides increased energy for making it through their training.

Fat Burner Supplement Safety

Although some supplements have promising effects, there are concerns about their safety. For instance, consuming too much caffeine is known to raise blood pressure. Increased blood pressure puts people at risk of heart attack and death.

In some cases, the use of a fat burner has led to other health issues. For instance, one case report connected this type of supplement with acute liver failure. Another linked a fat burner with the development of severe lactic acidosis. This is when the body produces more lactic acid than it can metabolize.

There’s also the risk that some fat burners will be contaminated with unsafe ingredients. One such ingredient is 2,4-Dinitrophenol or DNP. Research indicates that DNP has health risks for humans, to the point where they recommend it be banned for consumption. Yet, out of 94 supplements reviewed, 14 contained DNP.

DNP was used in medical practice in the 1930s but was found to have severe toxicity. So, it was withdrawn from use. Now it is used by bodybuilders and extreme dieters. It works by inhibiting energy production in the cells. This aids in fat loss.

So, What’s the Best Fat Burner?

While it’s important that you know the science behind fat burners, your clients likely want to know just one thing. What’s the best fat burner? Unfortunately, there is no one-size-fits-all answer to this question.

The best fat burner is one that is safe, first and foremost. This means that it contains legal, approved ingredients. At the same time, it’s important to use any supplement, fat burners included, according to the product instructions.

The product’s label will say how much is safe to take. Exceeding this dosage could lead to health issues. Also, because the effects of long-term use may not be entirely known, these substances may be best when used for short periods.

Most importantly, clients should pay attention to how they feel when taking a fat burner. Does it give them energy but also make their heart race? The health risks of the latter may outweigh the benefits of the former. Or maybe it suppresses their appetite so much that they don’t eat enough. While this may help avoid weight gain, it can also lead to nutritional deficiencies.

All weight loss pills come with some level of risk. To make sure this risk isn’t too high, clients should consult with their health providers. They can help decide whether a supplement is safe based on the client’s physical condition and health.

The Often-Forgotten Fat Burner

There is one fat burner that is readily available and cheaper than buying a dietary supplement. It also doesn’t have the safety issues associated with some fat burning ingredients. What is this magic fat burner? Water.

Johns Hopkins explains that the body needs water to burn body fat. But this natural fat burner also provides a few different weight loss benefits. They include:

  • It stimulates metabolism.

  • It helps suppress appetite.

  • It reduces calorie intake.

  • It supports energy and movement during workouts.

Thus, increasing water intake can help with weight loss—without taking a fat burner.

Other Healthy Ways to Increase Fat Metabolism

Another way to lose more body fat is to fuel your body according to your workout that day. For instance, on high-intensity days, boost your carb intake. This provides the energy you need to power through your workout. On low-intensity days, keep fat and carbs below 20% of your total intake. This helps keep the body in fat burning mode.

Strength training can also boost fat loss. The more muscle you have, the more calories your body burns, even at rest. This keeps your metabolic rate stoked throughout the day, making it easier to lose weight.

Want to help your clients make better nutritional choices? Become a Certified Nutritionist. With this specialization, you can teach clients how to build better habits for a healthier lifestyle.


Clark, J., & Welch, S. (2021). Comparing effectiveness of fat burners and thermogenic supplements to diet and exercise for weight loss and cardiometabolic health: Systematic review and meta-analysis. Nutrition And Health, 27(4), 445-459. https://doi.org/10.1177/0260106020982362

Pooyandjoo, M., Nouhi, M., Shab-Bidar, S., Djafarian, K., & Olyaeemanesh, A. (2016). The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obesity Reviews, 17(10), 970-976. https://doi.org/10.1111/obr.12436

Ferreira, G., Felippe, L., Bertuzzi, R., Bishop, D., Ramos, I., De-Oliveira, F., & Lima-Silva, A. (2019). Does caffeine ingestion before a short-term sprint interval training promote body fat loss?. Brazilian Journal Of Medical And Biological Research, 52(12). https://doi.org/10.1590/1414-431x20199169

Bagheri, R., Rashidlamir, A., Ashtary‐Larky, D., Wong, A., Alipour, M., & Motevalli, M. et al. (2020). Does green tea extract enhance the anti‐inflammatory effects of exercise on fat loss?. British Journal Of Clinical Pharmacology, 86(4), 753-762. https://doi.org/10.1111/bcp.14176

Maki, K., Reeves, M., Farmer, M., Yasunaga, K., Matsuo, N., & Katsuragi, Y. et al. (2008). Green Tea Catechin Consumption Enhances Exercise-Induced Abdominal Fat Loss in Overweight and Obese Adults. The Journal Of Nutrition, 139(2), 264-270. https://doi.org/10.3945/jn.108.098293

Hector, A., & Phillips, S. (2018). Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance. International Journal Of Sport Nutrition And Exercise Metabolism, 28(2), 170-177. https://doi.org/10.1123/ijsnem.2017-0273

Ferreira, G., Watanabe, A., Trevizoli, N., Jorge, F., Diaz, L., & Couto, C. et al. (2020). Acute Liver Failure Caused by Use of Fat Burner: A Case Report. Transplantation Proceedings, 52(5), 1409-1412. https://doi.org/10.1016/j.transproceed.2020.01.072

Huang, E., Omran, M., Patel, V., Newsome, A., & Bora, V. (2019). 1704. Critical Care Medicine, 47, 826. https://doi.org/10.1097/01.ccm.0000552443.21355.05

Petróczi, A., Ocampo, J., Shah, I., Jenkinson, C., New, R., & James, R. et al. (2015). Russian roulette with unlicensed fat-burner drug 2,4-dinitrophenol (DNP): evidence from a multidisciplinary study of the internet, bodybuilding supplements and DNP users. Substance Abuse Treatment, Prevention, And Policy, 10(1). https://doi.org/10.1186/s13011-015-0034-1

Yes, drinking more water may help you lose weight. The Hub. (2020). Retrieved 17 August 2022, from https://hub.jhu.edu/at-work/2020/01/15/focus-on-wellness-drinking-more-water/#:~:text=6.,published%20in%20Frontiers%20in%20Nutrition.

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