3 fat-burning hormones you've never heard of and how to get them.

Jade Teta ND, CSCS

In 2005 my brother Keoni and I wrote a paper entitled Hormonal Weight Loss: Is there such a thing as the Metabolic Effect? It was later published in the alternative medical journal Townsend Letter in February of 2007 under the name Hormonal Exercise for Fat Loss. This article can be found on our site at Hormonal Weight Loss

In that paper we detailed the science behind the metabolic after-burn known in exercise research as EPOC or oxygen debt, what we call Metabolic Effect. The paper made the point that this beneficial metabolic state can increase fat and calorie usage for 24 to 48 hours after the workout. It also showed that this was primarily provoked by a unique hormonal interaction that is induced by a large surge in catecholamines (a fancy name for adrenaline and similar compounds) which then trigger a hormonal cascade resulting in increased cortisol, human growth hormone (HGH), and Testosterone as well as a beneficial switch in the insulin to glucagon ratio. All of this, as well as other effects of intense exercise, add up to create the enhanced fat calorie usage during and after the workout.

3 muscle hormones (IL-6, Lactate, IL-15)

However, there is more to the metabolic after-burn than the hormones above or EPOC (EPOC may actaully be a relatively small portion of the afterburn). There are other key signaling molecules trainers and fitness enthusiasts must tap into if they hope to generate the most from shorter more intense workouts. Interleukin-6 (IL-6) is a signaling molecule released from muscle during exercise. With the right kind of stimulus, this compound can increase to 20 or 100 times over resting levels. IL-6 has been shown to act like a hormone and its job is to signal the muscle, fat, liver and brain about how to respond to intense exercise. The best way to think about IL-6 is as an "energy sensor". That is because as stored muscle sugar (glycogen) is depleted, IL-6 is released from muscle in greater and greater amounts. It leaves the muscle cell and signals fat tissue and other muscle cells to increase the burning of fat.

It also signals the liver to increase the production of sugar or glucose so that intense activity can be sustained. This is a process called gluconeogensis which uses glycerol from fat and amino acids from muscle to maintain blood sugar. At the same time, IL-6 stimulates the break down of sugar stores in the liver and process called glycogenolysis. Il-6 also communicates with the brain. Studies in rats seem to suggest it is impacting appetite. If you are interested in the detailed science of IL-6, it can be found here Antiaging Secret

Obviously IL-6 is extremely beneficial for fat loss seekers. Researchers have speculated it is the elusive "exercise factor" researchers have been seeking for sometime. It is useful for trainers to know how to use it. Interestingly, IL-6 release is not correlated with muscle damage. It is generated based on mechanical movement of muscles. The more muscle a persons moves the more IL-6 they produce. This is why multi-joint, multi-muscle movements are preferred by Metabolic Effect over single joint and isolated muscle movements. The other key is doing exercise that causes glycogen depletion. This means either long duration marathon type activities or high intensity sprint based exercise. Since long duration aerobic type exercise creates a negative response in terms of the cortisol/HGH balance, high intensity short duration activity is preferred. If you can get anaerobic quickly, you will burn through muscle sugar stores very fast. This will create a large IL-6 surge along with favorable growth promoting hormones.

Lactate is a hormone

Another key hormone released from the muscle is lactate or lactic acid. The idea that lactate is a hormone is a novel concept. But it has been made clear through several studies the last few years that lactate is a key signaling molecule in exercise metabolism. Interestingly, a lactate receptor called GPR81 was recently isolated confirming its hormone like action (1). Other studies have shown lactate can directly stimulate the release of testosterone, progesterone, and HGH. (2-4)

The major signal sent by lactate during exercise seems to be an "adaptation signal". When analyzing its signaling action, lactate has three major functions 1) as an alternate fuel source 2) to increase mitochondrial generation (the energy factories in our cells) and 3) to stimulate the release of growth promoting hormones including HGH and testosterone. As an alternate fuel source, lactate can make significant contributions to energy use during high intensity exercise. Dr. Chistopher Scott, out of the University of Southern Main, has demonstrated that neglecting the anaerobic energy contribution of lactate production can underestimate calorie use during exercise by up to 40% (5). Lactate production is also highly correlated with a much larger EPOC (metabolic after-burn). By virtue of its action on mitochondrial production, lactate has a strong role in increasing metabolic efficiency. Finally, because it is coupled so strongly to HGH and testosterone, lactate has a key role to play in muscle maintenance and fat loss.

Given lactate's key involvement in exercise metabolism, trainers and fitness enthusiasts should know how to harness its potential. In Metabolic Effect we use an integrated workout combining elements of weight and cardiovascular intervals. However, we also use a wide range of burnout techniques to generate a large lactate response. Pulses, 1/2 reps, holding reps, fast reps, slow reps, squeezing reps, you name it, you will see it in the ME workout. This is not because we are simply trying to work someone to death.

On the contrary, we use these techniques for the hormonal lactate response it creates. Studies on vascular occlusion demonstrate this type of training can create enhanced muscle and fat loss. And it is all about the buildup of metabolic products including lactate. The "burn" generated by this style of training is the key metabolic feedback mechanism to know you are getting the response. It is also a key component missing from many trainer's metabolic conditioning workouts.


interleukin-15 (IL-15) is another muscle molecule, technically known as a myokine, to be aware of. I refer to this molecule as the "Arnold molecule", as in Arnold Schwarzenegger the famous bodybuilder. I call it this because it has the unique action of stimulating muscle growth while increasing fat loss, a nifty trick that is extremely difficult to pull off. Harnessing IL-15 should be a chief goal of anyone wanting to change body composition. IL-15 release is generated through the action of type II muscle fibers. These fibers are activated during explosive movements, when lifting heavy weights, and when muscles are brought to full fatigue. Many trainers frown on mixing heavy weight training with aerobically taxing workouts claiming form will be sacrificed. At Metabolic Effect we do exactly what many avoid. We include heavy weight training movements such as squats, dead-lifts, and power-cleans, as well as explosive exercises such as squat jumps and sprints, within a metabolic conditioning circuit. The reason is IL-15.

Putting it together- The Bs and Hs

Obviously, harnessing the potential of these three hormones has clear advantages in body composition and sometimes can run counter to common dogma in fitness; i.e., you should not do heavy weight training when pre-fatigued, burnout techniques have no place in metabolic conditioning, etc. The fear here is safety and the rest-based training format keeps the workouts self-determined and self-limited to increase safety.

In order to help understand which hormones are activated and when, there are 4 biofeedback tools trainers and fitness enthusiasts can use to know they are getting the correct hormonal response. We call them the Bs (Breathless & Burning) and Hs (Heavy & Heat). Obviously, depending on your goals, all are not necessary, but when the goal is fat loss and muscle maintenance trying to accomplish all four in your workout will generate the proper hormonal response allowing you to take advantage of IL-6, lactate, and IL-15.

Breathless- This correlates to the release of adrenaline, noradrenaline, and IL-6 and is correlated with EPOC.

Burning- This correlates with Lactate and IL-6 and HGH and to a lesser degree testosterone.

Heavy- This correlates with IL-15 and Testosterone and to a lesser degree HGH

Heat- Gives insight into the magnitude of the adrenaline surge which is correlated to the magnitude and length of EPOC. It also gives and indication of total calorie burn.

1) Journal of Biological Chemistry. 2009 Jan;284(5):2811

2) Journal of Cellular Biochemistry 2001;83:147-154

3) American Journal of Physiology. 1996 Nov;271(5 Pt 1):E910-5.

4) British Journal of Sports Medicine 2009;43: 521-525

5) Journal of the International Society of Sports Nutrition 2005;2(2):32-37



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