Many clients come to you because they want to start an exercise program that will help them achieve and maintain a healthy body weight. While some are motivated by aesthetic concerns, others recognize that excess body weight increases the risk for numerous chronic health conditions, including type 2 diabetes, heart disease, musculoskeletal injuries and back pain. What many people don’t realize, however, is that excess body fat can also disrupt the production of hormones that help to regulate energy metabolism, which, in turn, makes losing weight even more challenging. This article explains the link between hormones and metabolism and examines the modifiable lifestyle habits that can influence hormone production. 

A number of hormones are involved in regulating human metabolism; for this article, however, we’ll look at the hormones that help control hunger and energy metabolism—specifically, ghrelin, leptin, glucagon, insulin, epinephrine, norepinephrine and cortisol—because they respond to modifiable lifestyle habits. For example, adipose tissue (or body fat) has been recognized as an organ that helps regulate the production of specific metabolic hormones such as leptin. And research shows that excessive food intake combined with physical inactivity quickly results in an accumulation of fat stored in adipose tissue, which disrupts the normal function of the endocrine system, particularly the hormones required for efficient energy metabolism.

As a health and exercise professional, you can help your clients adopt healthy lifestyle habits, such as exercising regularly, consuming a wide range of nutrients at an appropriate caloric intake, and practicing good sleep hygiene, all of which can influence the types and amounts of hormones produced by the endocrine system. With a deeper understanding of how metabolic hormones function in reaction to exercise and lifestyle habits, you can identify appropriate behavior-change strategies that will make it more likely that your clients will achieve their health and fitness goals. 

Metabolism 101

Metabolism refers to the chemical reactions required for converting macronutrients into energy to support the body’s normal physiological function. The total energy needs of the body are the sum of the resting metabolic rate (RMR), which is the amount of energy the body expends to maintain physiological homeostasis while the body is at rest; the thermic effect of food (TEF), which is the amount of energy used to digest and metabolize food; and the thermic effect of physical activity (TEPA), which is the energy to support all physical activity and may include exercise as well as normal activities of daily living. Ideally, the amount of energy consumed via daily dietary intake equals the amount required to fuel these activities. Not consuming enough energy may result in a caloric deficit because reserves of stored energy would be used to fuel activity, which would result in weight loss. On the other hand, consuming more energy than is needed may result in a surplus of energy and weight gain in the form of fat. 

Energy is neither created nor destroyed; it is transferred from one state to another. Specifically, it is transformed from stored potential energy to being released as kinetic energy. The human body uses two types of energy—mechanical and chemical. 

  • Mechanical energy is created during the stretch−shortening cycle of muscle and elastic connective tissues. As the connective tissues rapidly lengthen, they store mechanical energy that is released as they return to the original resting length. For example, when quickly lowering the body to prepare for a jump, the calf, gluteal and quadriceps muscles are rapidly lengthened, storing mechanical energy that is then released as the muscles return to the original position by shortening. It is that shortening that generates the energy for the upward movement in a jump.
  • The second form of energy is chemical, in the form of adenosine triphosphate (ATP) used by muscle cells to fuel contractions. Chemical energy can also be either kinetic and used immediately to fuel cellular activity, or potential and stored for later use. Macronutrients consumed in the diet are either metabolized into ATP and used immediately in the release of kinetic energy or stored as potential energy in the form of glycogen in muscle cells or fat in adipose tissue to be used later. Fats and carbohydrates are the primary sources of ATP; however, while the primary purpose of protein is to repair damaged tissues, it can be metabolized into ATP to conserve glucose through a process termed gluconeogenesis.

Hormones and Metabolism

Hormones are chemicals produced by glands or organs that control how cells and tissues function. The hormones produced by the endocrine system metabolize macronutrients consumed in the diet into the ATP that fuels all cellular activity including the muscles responsible for physical activity. A hormone can only react with specific binding receptors in cells; for example, peptide hormones interact with receptors on the cell membrane, while steroid hormones interact with receptors on the nucleus of a cell. Hormones function to either stimulate or inhibit reactions within specific cells that contain the appropriate receptors and many different hormones support metabolism to ensure energy availability.

Hunger Hormones: Ghrelin and Leptin

The hormones ghrelin and leptin control hunger and satiety, respectively. Ghrelin is produced by the stomach and stimulates feelings of hunger. Ghrelin creates a direct connection between the gut, where food is digested, and the brain, where it crosses the blood-brain barrier to stimulate the lateral hypothalamus to create the signal for hunger. Leptin is produced by fat cells in adipose tissue to suppress hunger and stimulate energy expenditure. Research indicates that people with obesity have higher levels of ghrelin and lower levels of leptin, which could result in the tendency to consume too many calories at mealtime. It is also worth noting that inadequate sleep could result in elevated levels of ghrelin and lower amounts of leptin. In addition to increasing their levels of physical activity to metabolize fat into energy, helping clients to improve the quality and quantity of sleep could promote the optimal levels of ghrelin and leptin needed to control hunger, which is a key component for sustaining a healthy body weight. 

Hormones That Regulate Blood Glucose: Glucagon and Insulin 

To help ensure that energy is always available or stored where it can be accessed when needed, the pancreas produces glucagon to increase the amount of glucose available in blood or insulin to promote the storage of glucose into tissues. Glucagon is released in response to low levels of blood sugar to stimulate the release of free fatty acids from adipose tissue and to increase blood glucose levels, both of which are important sources of the ATP used during exercise. When more glucose is needed during exercise, glucagon can release additional glycogen stored in the liver, which is then converted to glucose before being metabolized to ATP. When food is consumed and is in the process of being digested, glucose is released into the bloodstream. In response, the pancreas releases insulin to promote the storage and absorption of glucose into cells to reduce blood glucose. Glucose is stored as glycogen in the liver and muscle cells, and excess glucose can be stored in the fat cells of adipose tissue. At the start of an exercise session, the sympathetic nervous system suppresses the release of insulin so that glucose can be more readily available to fuel muscle activity.

The Energy Hormones: Cortisol, Epinephrine and Norepinephrine

Cortisol is a steroid hormone produced by the adrenal gland in response to stress, low blood sugar and exercise. Cortisol supports energy metabolism during exercise by facilitating the breakdown of triglycerides and carbohydrates to create the glucose necessary to help fuel exercise. It can also inhibit protein synthesis and reduce the inflammation that is essential for post-exercise tissue repair. To preserve blood glucose levels or when glucose is not readily available, cortisol can convert protein to glucose via a process called gluconeogenesis. 

Clients who exercise at a moderate-to-high intensity for more than 60 minutes without consuming a sports drink or gel are at risk of having protein rather than fat or carbohydrate used for fuel, which could work against their weight-loss goals. If a client is going to exercise at a high intensity for a prolonged period, a low-calorie sports drink could help ensure optimal substrate utilization so that protein is conserved for tissue repair rather than used to fuel activity. In addition, too much high-intensity exercise without an appropriate amount of recovery, including sleep, could result in elevated cortisol levels that would impede the ability of the post-exercise tissue-repair process. Finally, during exercise or periods of stress, cortisol can also suppress the body’s immune system; an accumulation of stress, either from overtraining or other external sources, could weaken the immune system.  

The hormones epinephrine and norepinephrine work together to produce energy and regulate cardiorespiratory function during exercise and are often referred to as adrenaline because they are produced by the adrenal gland. Once the body starts exercising, the physical stress signals the hypothalamus to release epinephrine and norepinephrine from the adrenal gland to elevate cardiac output, dilate blood vessels to enhance blood flow, increase blood glucose (to help fuel exercise) and support the metabolism of free fatty acids into ATP. Glucagon, epinephrine, norepinephrine and cortisol work together to increase circulating glucose prior to and during exercise. The amount of glucose released by the liver and epinephrine produced by the adrenal gland depends on the intensity and duration of exercise. 

Table 1 summarizes the production and function of the seven hormones related to metabolism.





Adrenal medulla (inner adrenal cortex)



Physical (exercise) or emotional stress 

Increases heart rate; increases blood sugar by breaking down glycogen (glycolysis); involved in fat metabolism for energy


Similar in function to epinephrine; also functions as a neurotransmitter to facilitate nerve signals and constrict blood vessels, which increases blood pressure

Adrenal cortex (outer) 

Cortisol (glucocorticoid) 

Physical (exercise) or emotional stress

Releases free fatty acids to be metabolized into adenosine triphosphate (ATP) for energy (fat metabolism); suppresses the immune system; conserves glucose by converting protein to ATP (gluconeogenesis); inhibits protein synthesis



Elevated levels of blood glucose

Reduces blood-glucose levels by promoting storage of glucose in muscle cells and the liver (stored as glycogen) 



Reduced levels of blood glucose

Elevates levels of blood glucose to provide energy for exercise



Anterior pituitary gland releases ghrelin to stimulate hunger in response to glucose levels

Stimulates hunger signals; increases acid secretion for digestion


Adipose tissues (body fat) 


In response to insulin levels

Signals satiety (stop eating) 



Resistance and Sensitivity 

Many hormones are released in bursts in response to specific stimuli, such as when glands react to a chemical signal received by receptors or direct neural stimulation. For example, the body won’t just elevate cortisol to release free fatty acids; rather, stress is the stimulus that causes cortisol to be released by the adrenal cortex. Hormone sensitivity means that an ample number of receptors are available in cells to allow a hormone to function efficiently. For example, strength training can improve the ability of type-II muscle cells to convert glucose to ATP, resulting in improved insulin sensitivity, which is the ability of insulin to transport glucose to muscle cells. Conversely, a hormone is said to experience resistance when there are not enough receptors available in cells to react with it. As a result, the hormone won’t be able to perform its function efficiently. For example, obesity could result in leptin resistance, which is a lower amount of receptor cells for leptin to interact with once it is produced to suppress hunger. In fact, research has shown that insulin resistance and abdominal obesity are associated with low soluble leptin concentrations.

Chronic insulin resistance could result in type 2 diabetes, meaning the cells in your muscles, fat, and liver don’t respond well to insulin. This causes the pancreas to make more insulin but it is not able to produce enough to promote effective uptake of blood glucose into cells. Regular exercise, such as strength training, can enhance insulin sensitivity by promoting an increase of receptor cells that allow the hormone to function. Conversely, a sedentary lifestyle could result in insulin resistance, which means there are fewer receptor sights where the hormone can perform its intended function. Encouraging clients to stick with their exercise programs, including resistance training, to improve glycogen metabolism can help ensure optimal insulin sensitivity, which, in turn, reduces their risk of developing type 2 diabetes. 

Circadian Rhythms 

Circadian rhythms determine the body’s innate sense of time and how hormones respond to levels of light and darkness. Melatonin is a hormone that lowers the body’s temperature in preparation for sleep; too much light in the evening or nighttime could lower melatonin production, thus making it harder to fall asleep. When you’re unsuccessfully trying to fall asleep, your body might think it needs energy and starts releasing cortisol to stimulate energy production, making it difficult to fall asleep even when you feel tired. If you or your clients struggle to get to sleep, limiting screen time in the later evening hours to allow circadian rhythms to be more aligned with the natural light cycles could help. If your clients complain about not getting enough sleep, help them to examine their evening routines and identify areas where simple adjustments might result in better sleep hygiene. (We’ve included some exclusive content for ACE Certified Professionals on how to talk to your clients about sleep hygiene and help them create habits that promote high-quality sleep.) In addition to reducing overall stress and helping to lower cortisol levels, increasing the quantity and quality of sleep could also help clients manage a healthy body weight.

Helping Clients

Measuring a client’s hormone levels requires specialized training and the ability to work with an appropriate lab that can conduct the testing. While it is outside your scope of practice to evaluate lab results and make exercise program design decisions based on the results, it may be worth considering how you might expand your professional network to include medical professionals qualified to interpret lab results detailing hormone levels. Together, you could design an exercise program based on the unique hormone profile of the client.

Melanie Rogers, MS, FDN-P, is a functional health coach in San Diego who has clients tested at a lab to identify their hormone levels. “Identifying hormone levels through lab testing and symptom correlation is key for understanding clients overall metabolic health,” explains Rogers. “The information allows me to make customized adjustments in their programming. For example, monthly fluctuations in estrogen and progesterone in women can influence the ideal timing for strength, high-intensity interval training (HIIT) and recovery workouts. In addition, understanding a client’s cortisol levels can determine the level of intensity at which they should be exercising. Understanding the hormone profiles of a client allows me to utilize physical activity as a tool to support their body’s needs and to make sure not to inappropriately overload the body.”

While it is possible to test for levels of ghrelin, leptin, glucagon, insulin, cortisol, epinephrine and norepinephrine, simply knowing how lifestyle habits influence levels of these hormones is important to helping your clients achieve their goals. Guiding your clients to adopt healthier habits such as regular exercise, good nutrition and proper sleep could support a more efficient endocrine system that promotes optimal energy metabolism. Applying the ACE Integrated Fitness Training® (ACE IFT®) Model to design exercise programs for clients that include workouts for functional strength, cardiorespiratory fitness and mobility can be an effective way to improve the efficiency of metabolic hormones. Additionally, helping clients lose excess body fat while gaining muscle could enhance the functioning of hormones such as ghrelin, leptin and insulin. Leptin and insulin, for example, are produced in response to eating. Insulin is released first to promote the uptake of glucose, and then leptin is produced to signal the sense of being full. Asking clients about their eating habits, such as whether they eat quickly or take their time during a meal, could identify an area for behavior modification. Advising clients to slow down while eating or to thoroughly chew their food could help these hormones to function more effectively, reducing a tendency to overeat. 

You can also help clients identify an appropriate caloric intake to support their daily activity and educate them about healthy nutrient selection and portion control, both of which could aid in their efforts to achieve a healthy body weight. In addition, encouraging clients to consume a healthy post-exercise snack that contains all macronutrients replaces muscle glycogen used during exercise and promotes repair of damaged muscle proteins and satiety by supporting optimal levels of insulin, ghrelin and leptin. Finally, helping clients identify their natural circadian rhythms and optimal times to eat and/or exercise based on personal needs may also be effective for restoring optimal endocrine function.  

All Clients Want the Same Thing

Your clients come to you with the same basic expectation: results. In some cases, a client simply needs to make a few simple adjustments to their exercise program to achieve their desired goals. In other cases, however, a client may need to make other lifestyle changes to achieve the results they want. Understanding how the body produces hormones in response to exercise, as well as the roles that sleep and nutrition play in establishing optimal function of the endocrine system, provides you with important tools for helping each client achieve their desired results. 

In this video, ACE Pro Pete McCall explains the link between hormones and metabolism and examines the modifiable lifestyle habits that can influence hormone production.