3 Fat-Burning Hormones You’ve Never Heard Of

by Dr. Jade Teta ND | Follow on Twitter

Marathons, weight training, sprints or aerobics classes? Which one is best for fat loss?

Note: 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.

THE SCIENCE BEHIND THE METABOLIC AFTER-BURN known in exercise research as EPOC or oxygen debt, is what we call Metabolic Effect.

This beneficial metabolic state can increase fat and calorie usage for 24 – 48 hours after the workout. It is primarily provoked by a unique hormonal surge of catecholamines (adrenaline and similar adrenal compounds) which then trigger a hormonal cascade resulting in the increase of:

  • Cortisol
  • Human growth hormone (HGH)
  • Testosterone and
  • A beneficial switch in the insulin to glucagon ratio.

This hormonal cascade along with other effects of intense exercise, create the enhanced fat and calorie usage during and after the workout.

The Trio Muscle Hormones (IL-6, Lactate, IL-15)

However, there is more to the metabolic after-burn than the hormones above.

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.

1) IL-6: High-Intensity, Short-Duration Activities

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, a 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 at 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 practitioners 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 over single joint and isolated muscle movements. The other key is doing exercises 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.

2) Lactate: Intervals and Burnout

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 in 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, especially during high intensity exercise
  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, which plays a key role in muscle maintenance and fat loss

Dr. Chistopher Scott, out of the University of Southern Main, has demonstrated that neglecting the anaerobic energy contribution of lactate production can underestimate calories 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.

Given lactate’s key involvement in exercise metabolism, practitioners and fitness enthusiasts should know how to harness its potential. In Metabolic Effect (ME), 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. For example:

  • Pulses
  • 1/2 reps
  • Holding reps
  • Fast reps
  • Slow reps
  • Squeezing reps, etc

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 build-up 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 desired response.  It is also a key component missing from many metabolic conditioning workouts.

3) IL-15: Mixing Heavy with Explosive

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
  • When muscles are brought to full fatigue

Many fitness 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

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.

In order to help understand which hormones are activated and when, there are 4 biofeedback tools physicians and trainers can use to know they are getting the correct hormonal response. We call them the Bs (Breathless & Burning) and Hs (Heavy & Heat).

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

About the Author
Dr. Jade Teta ND

Dr. Jade Teta is an integrative physician specializing in natural health, fitness and body transformation. He is the co-author of The Metabolic Effect Diet. He completed his undergraduate training at North Carolina State University, earning a bachelors of science in biochemistry. He then went on to study at Bastyr University in Seattle, Washington completing his doctorate in Naturopathic medicine. Dr. Teta has worked in the fitness and weight loss fields for over 20 years, and is the co-developer of the rest-based training system for personal training and group exercise. He is also the co-founder of the Naturopathic Health Clinic of North Carolina and of the health, fitness and international fat loss company, Metabolic Effect. His background in natural medicine, along with his fitness expertise, has defined his healthcare specialties of hormonal weight loss and functional medicine approaches to chronic disease.