Written by Michael J. Rudolph, Ph.D.
10 September 2021

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Fat Burners: Nutrition and Supplements That Increase Fat Metabolism


By Michael J. Rudolph, Ph.D.


It is not just the quantity of protein in your diet that reduces body fat, but also the quality of protein consumed that has a significant effect on fat loss.


For the bodybuilder or athlete, too much body fat is bad for business. Because of this fact, bodybuilders and athletes have become pretty efficient at reducing body fat. Of course, as a bodybuilder you can never be too ripped and as an athlete there is typically an advantage to being leaner. The customary approach used to decrease body fat decreases caloric consumption while increasing fat burning. Reducing food intake or caloric consumption can be grueling, especially if the food you’re ingesting doesn’t mitigate hunger to some degree. Furthermore, reducing food intake also tends to decrease the body’s energy expenditure or metabolic rate – primarily due to a reduction in lean body mass and an enhanced metabolic efficiency.


Energy-sparing mechanisms such as those delineated above are counterproductive, and diminish the ability to burn body fat. Approaches that decrease hunger and impede fat-saving compensatory mechanisms should catalyze fat loss. Consequently, a diet supplemented with the right macronutrients – such as high-quality protein – that stimulate energy expenditure and decrease hunger should ease the difficulty from a low-caloric diet that causes fat loss. Furthermore, novel compounds that reverse the energy-sparing mechanisms by increasing fatty acid oxidation and/or thermogenesis should also be extremely effective at reducing body fat for both the athlete and bodybuilder. 


High-Quality Protein Loaded in Essential Amino Acids Decreases Body Fat


It is not just the quantity of protein in your diet that reduces body fat, but also the quality of protein consumed that has a significant effect on fat loss. Protein quality is defined as the percentage of essential amino acids to total protein consumed, and diets with greater levels of essential amino acids (protein quality) increase fat loss. Previous studies have clearly shown higher protein in the diet decreases body fat, yet one investigation by Loenneke et al.1 demonstrated that consuming high-quality protein rich in essential amino acids may be the more precise way to reduce body fat.


In the aformentioned study, 27 male and female subjects had their diets monitored for the consumption of quality protein, with the threshold being 10 grams of essential amino acids per meal. At the conclusion of the study, body fat measurements were made and the individuals who consumed the highest quality of protein had the greatest decrease in body fat. Putatively, high-quality protein enhances fat loss because essential amino acids, especially leucine, stimulate muscle protein synthesis – leading to greater muscle mass. The increase in muscle boosts metabolic rate and the consumption of fatty acids, leading to fat loss. In addition, the essential amino acid leucine inactivates the energy-sensing molecule AMPK. The inactivation of AMPK in the brain decreases hunger, therefore lowering caloric consumption and further stimulating fat loss.2


Caffeine and Carnitine Independently Stimulate Fat Loss, but Robustly Stimulate Fat Loss When Consumed Together


Caffeine is the active ingredient in coffee that stimulates the central nervous system, impeding drowsiness and restoring alertness. For the athlete or bodybuilder, caffeine can be used to burn fat by increasing the cellular concentration of the molecule cyclic AMP – which indirectly stimulates fatty acid oxidation and thermogenesis,3 leading to fat loss. A classic analysis by Acheson et al.4 demonstrated that caffeine consumption triggered an increase in free fatty acid levels accompanied by a significant increase in fat oxidation. In another study supporting the thermogenic role of caffeine, Belza et al.5 showed that ingestion of 50 milligrams of caffeine in 12 healthy young men triggers thermogenesis. Several hours after caffeine intake, the researchers measured an increase in thermogenesis of 6% as compared to the placebo.

Interestingly, another investigation illustrated that the fat-burning effects of caffeine are attenuated by chronic consumption of caffeine – suggesting that caffeine may not be an effective fat burner when consumed independently.


Carnitine shuttles fatty acids into the mitochondrion where they are burned for energy, potentially initiating fat loss. However, despite this well-established fact, carnitine has been shown in several studies6 to have no influence on fat burning or fat loss when consumed alone. Conversely, an investigation by Wall et al.7 demonstrated a novel way to increase muscle carnitine levels, thus facilitating fatty acid oxidation and fat loss.


In the study by Wall et al., researchers gave subjects carnitine while simultaneously administering insulin and glucose for a total of five hours. This treatment generated a significant increase in carnitine levels, which stimulated fat oxidation during high-intensity submaximal exercise. Interestingly, when more insulin was administered, carnitine levels also increased. This finding suggests that cellular uptake of carnitine might be enhanced when taken together with a glucose-rich meal that stimulates insulin secretion. As a result of the increased carnitine levels, there was a reduction in muscle glycolysis and an increase in glycogen levels accompanied by an increase in fatty acid oxidation – potentially leading to fat loss.


Because caffeine directly stimulates the production of fatty acids via lipolysis and carnitine stimulates the burning of fatty acids, caffeine and carnitine may act synergistically when consumed together. A study by Cha et al.8 demonstrated this fact by giving 250 athletes a sports drink that contained 15 grams of carnitine alone, 5 milligrams of caffeine alone or 15 grams of carnitine with 5 grams of caffeine. Also, a control group received a placebo. One hour after ingesting the drink, the test subjects rode a stationary cycle for 45 minutes at a moderate intensity followed by a period when the athletes increased their cycling intensity to 80 percent of their maximum capacity. The study results indicate that combining carnitine and caffeine packs a powerful fat-burning punch.


What did Cha et al. find? According to the researchers' measurements, the athletes in the group that consumed both carnitine and caffeine kept cycling at 80 percent of their maximum capacity for twice as long as the athletes in the control group. Furthermore, in the group that consumed carnitine along with caffeine, the level of fatty acid was significantly increased at exhaustion time compared to the groups that independently consumed carnitine or caffeine – demonstrating a considerable increase in fat being burned in the group consuming carnitine and caffeine, potentially increasing fat loss.


For most of Michael Rudolph’s career he has been engrossed in the exercise world as either an athlete (he played college football at Hofstra University), personal trainer or as a research scientist (he earned a B.Sc. in Exercise Science at Hofstra University and a Ph.D. in Biochemistry and Molecular Biology from Stony Brook University). After earning his Ph.D., Michael investigated the molecular biological effects of exercise as a fellow at Harvard Medical School and Columbia University. That research contributed seminally to understanding the function of the incredibly important cellular energy sensor AMPK – leading to numerous publications in peer-reviewed journals including the journal Nature. Michael is currently a Senior Scientist working at the New York Structural Biology Center where he investigates the molecular nature of human illness and disease.










1. Loenneke JP, et al. Quality protein intake is inversely associated with abdominal fat. Nutr Metab (Lond), 2012; 9(1): p. 5.


2. Saha AK, et al. Downregulation of AMPK accompanies leucine- and glucose-induced increases in protein synthesis and insulin resistance in rat skeletal muscle. Diabetes, 2010; 59(10): p. 2426-34.


3. Cao W, et al. p38 mitogen-activated protein kinase is the central regulator of cyclic AMP-dependent transcription of the brown fat uncoupling protein 1 gene. Mol Cell Biol, 2004; 24(7): p. 3057-67.


4. Acheson KJ, et al. Caffeine and coffee: their influence on metabolic rate and substrate utilization in normal weight and obese individuals. Am J Clin Nutr, 1980; 33(5): p. 989-97.


5. Belza A, Toubro S, et al. The effect of caffeine, green tea and tyrosine on thermogenesis and energy intake. Eur J Clin Nutr, 2009; 63(1): p. 57-64.


6. Villani RG, et al. L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. Int J Sport Nutr Exerc Metab, 2000; 10(2): p. 199-207.


7. Wall BT, et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol, 2011; 589(Pt 4): p. 963-73.


8. Cha YS, et al. Effects of carnitine coingested caffeine on carnitine metabolism and endurance capacity in athletes. J Nutr Sci Vitaminol (Tokyo), 2001; 47(6): p. 378-84.