These undercover agents are responsible for almost every benefit you get from working out. Harness their power to burn more fat, build lean muscle, and boost your total health.

Portrait of Tammy Strobel

These undercover agents are responsible for almost every benefit you get from working out. Harness their power to burn more fat, build lean muscle, and boost your total health. 

<b>PHOTO</b> 123RF.COM
<b>PHOTO</b> 123RF.COM

Every time you exercise, special hormones in your body spring into action. Released by your system when you move, they give you energy, spark your motivation, and boost your mood. “Hormones are essential for your ability to work out effectively,” says Katarina Borer, a professor of movement science and the director of the Exercise Endocrinology Laboratory at the University of Michigan. “They improve your heart and lung function, they bring fuel to your muscles, and they help your body recover afterwards.” Even so, these exercise hormones are virtually unknown and underappreciated – but that’s about to change. 


This hormone is produced by your bones when you work out. Its job: to encourage your muscles to absorb the nutrients that help them perform at their peak. “In women, though, osteocalcin production begins to decrease around age 30,” says Gerard Karsenty, the chair of the genetics and development department at Columbia University Medical Center. As levels drop off, he says, your nutrient-depleted muscles can’t work as hard. 

Fortunately, regular exercise may bump up your production of osteocalcin, and that extra boost can elevate your performance, Gerard says. His research found that women’s levels were higher after they worked out for 45 minutes; in another study, the muscles of animals that were given a dose of the hormone functioned as effectively as those a fraction of their age. Hit the gym at least every other day to keep your levels up, Gerard suggests. 


Your brain prompts the release of this powerful stress hormone when you work out. And that’s a good thing. “Noradrenaline stimulates the metabolism and helps your heart and lungs respond properly to exercise,” says Jill Kanaley, a professor and associate chair of nutrition and exercise physiology at the University of Missouri. It also makes you more resilient to mental stress. In addition, noradrenaline helps turn white fat into brown, just like irisin, according to a study from Brigham and Women’s Hospital in Boston. 

The longer or harder you move, the more noradrenaline you produce, Katarina says. Your best bet: Add short, super high-intensity bursts to your regular routines. 


The gut secretes this to help you feel full. But exercise also triggers the production of peptide YY (PYY), according to research in the journal Appetite. “People who exercise more frequently produce more PYY than others, but levels can rise after a single workout,” says Leslie Bonci, a sports dietitian and a sports nutrition adviser for nutritional supplements brand Klean Athlete. The relationship between PYY and hunger is complex. “You might feel ravenous immediately after exercising but less hungry an hour later as levels of the hormone continue to climb,” Leslie says. Overall, you’ll feel more satisfied with smaller portions. 

Weight-bearing aerobic exercises, like jumping rope and playing tennis, are the most effective at suppressing appetite, research indicates. Experts aren’t sure why, but it may be because these activities engage your gut, where PYY is produced. You can maximise that effect by eating about 0.6g to 0.8g of protein per 0.5kg of bodyweight daily, Leslie says. “People with diets that are higher in protein tend to produce extra PYY,” she explains. 


These include hormones as well as hormone-like substances that help build your muscles – and your brainpower. When you work out, the body releases hormones such as insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF), along with proteins like brain-derived neurotrophic factor (BDNF). “IGF-1 and VEGF help repair the muscle damage caused by exercise, helping to build the fibres back stronger,” says Gerard. 

The growth factors may also strengthen your memory and cognitive function. Different types of workouts are best at boosting each growth factor, Katarina says. For instance, HIIT exercises raise VEGF, lifting heavy weights raises IGF-1, and high-intensity endurance aerobic activities like running raise BDNF levels. To score all three, change up your routine regularly. 


This increases the activity of the genes that convert white fat cells into brown, a beneficial type of fat that can burn calories, according to researchers from the University of Florida College of Medicine. Irisin may reduce white fat stores, too. Tissue samples that were exposed to irisin had up to 60 per cent fewer mature fat cells than others, the study authors say. 

Workouts that target large muscle groups like your glutes, quads, or chest typically release more irisin than exercises that work smaller muscles such as biceps or calves, since bigger muscles contain more of the hormone, Leslie says. She suggests endurance activities such as running or high-intensity strength workouts like Crossfit. 

There’s also evidence that increasing levels of melatonin, the sleep hormone, bumps up the production of irisin. Eating melatonin-rich foods like walnuts and tart cherries before bed will help you sleep better and burn more fat, Leslie says.