How physical activity and diet change our personal training clients’ bodies is indeed top of mind in our industry. Low fat, low carbohydrate, high protein, aerobics, resistance training, etc. are all diet and activity strategies that will to some degree alter our bodies. Even a poor diet and no exercise will make changes, too. Regular exercise and diet influence key hormones and metabolism, and employing different strategies can alter success. But there is complex biochemistry at play to make such changes.

Altering your metabolism by manipulating diet and activity is the overall objective, but understanding “the how” diet and exercise actually do can make all the difference in the world; one can tune and sharpen it for fast, precise results. When diet and exercise strategies are employed together to achieve the goals of fitness and health, the synergism is more effective. First, we’ll look closely at the interplay between exercise and hormone function, and the following article will break down the interplay between diet and hormones.

Key Hormones and Metabolism

Bridging the gap between our efforts to be healthy and fit and what we see in the mirror is a biochemical science that is in motion all the time. In general, we call this our metabolism–an unconscious process directed by chemical signals that the body produces in response to our input and output of energy. With the correct inputs and outputs, we can direct our body’s metabolism with impressive accuracy. What we think, how we act, what we do, what we eat, and the outcome of what we look like is rarely a coincidence. There is a connection.

Connections and communications between our body’s organs and their pathways have been studied and discussed for thousands of years. Mind-body connections can be divided into several pathways: conscious, unconscious, and further into neural, hormonal, and neurohormonal pathways.

Conscious connections are those directives from the brain to the body, instructing some type of purposeful action. Unconscious connections occur when the brain instructs the body to perform a vital function without your awareness: you breathe in and out to get oxygen, your heart pumps blood, neurotransmitters are released.

The central nervous system, autonomic nervous system, sympathetic and parasympathetic modes are responsible for these signals. But for the sake of keeping it simple and not over-complicating an already complex interaction of body systems, this will be a brief overview of these systems and the metabolism.

The Communication Between Body Systems

The nervous system, endocrine system, immune system, digestive system, circulatory system, and the musculoskeletal system all work in harmony and are synchronized by constant and complex communication systems. There are many other sub-systems among these mentioned and they are important in metabolism, but again this just a brief overview. These systems communicate, regulate, and provide information and feedback with chemical and electrical signals from organs, glands, and tissues.

This communication, regulation, and manipulation of the endocrine system is the most powerful process that can change the composition of the human life form. If one can manipulate the hormones that the body produces an important key to change has been harnessed. All the exercising and dieting in the world will not change your body unless the endocrine secretions are not stimulated to make the body change.

Knowing what hormones do can benefit you in the process of transformation.  All diet and exercise programs are not equal and their hormonal responses are different as well. This is crucial in being successful and is one of the biggest reasons why most people fail at changing their bodies. Knowing everything about the endocrine system is not necessary to change the human body, but a few key functions of it will need to be understood.

The Endocrine System

The most relevant endocrine mechanisms and actions deal with energy usage, access, and storage. The hormonal actions that are primarily responsible for weight loss, weight gain, and body composition can be manipulated with diet, supplements, and exercise. Knowing how to manipulate these hormones optimally is really the key to effective body transformation.

The combination of reducing body fat (if body fat needs reduction), increasing lean body mass, and elevating the body’s metabolism at the same time is actually quite simple when exercise and diet work hand-in-hand. By increasing the metabolic rate the body normally will reduce body fat or body fat storage as a result if extra calories are not increased at the same time.  In general, any time that exercise is introduced, calorie-burning increases to perform the work being done which causes an increase in the body’s metabolism.


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How Exercise Influences the Endocrine Hormones

Exercise stimulus can be linked to a hormonal response. Depending on the type of exercise and the intensity of the exercise, research has demonstrated large shifts in hormonal outputs take place to increase metabolism, reduce body fat, and increase lean body mass.

Testosterone and growth hormone outputs are increased from the response of physical stress stimulus, among others. These hormones are being secreted all the time and are working on your body. One doesn’t build muscle in the gym but merely creates the stimulus to promote and influence key hormones that create the change.

Repetitive exercise stimulus changes the regulation and output of these hormones and over the course of time the body changes. This is the missing link that many fail to understand and why attempts to change the human physique fall short.

The Impact of Resistance and Aerobic Training on Hormones

Resistance training and aerobic training both burn calories, but differ in their stimulation of key hormones. Resistance training raises the metabolism by creating muscular trauma and breakdown that will need to be repaired. Hormones are secreted and rejuvenation starts.

This can last as long as 72 hours or more. This rejuvenation process needs lots of energy to fuel the construction of new muscular proteins. The additional muscle that will be added requires more energy and can do more work the next time you train. Thus, more energy will be spent while you are exercising, while you are recovering, and to maintain the newly acquired muscle, all while you are at rest.

Aerobic training utilizes energy–sourced from carbs and fat in the presence of a positive energy balance–to perform work for an extended period of time. As carbs and fat are consumed by the working muscles, hormones are stimulated in response to replace these energy stores in the muscles from our adipose tissue and liver. This is how adipose tissue is reduced from aerobic training.

Both types of exercise stimulus are effective at reducing body fat but each has a different pathway of metabolism that can impact appearance. The most effective training program utilizes both strategies in the optimal balance. One approach is necessary for long-term metabolism shift and the other for immediate stored energy conversion.

Resistance training triggers anabolism (tissue building) and aerobic training triggers catabolism (tissue breakdown). Together these two strategies work together synergistically making them more effective than either of them by themselves.

The “Magic” of Exercise

These physiological changes potentially can be measured by the mirror or the scale, but the real magic from hormonal manipulation via exercise lies in the benefits that these hormones have on the rest of the body’s organs and systems. The brain and nervous system functions are enhanced by testosterone, growth hormone, adrenaline, epinephrine, and other hormones secreted in optimal ratios courtesy of physical activity.

The heart, lungs, liver, kidneys, digestive tract, immune, and lymphatic systems are all tuned and sharpened in response, too. This is why people that exercise regularly can and do live longer and have a higher resistance to disease. Not only does one look stronger and healthy but the body as a whole becomes stronger, more efficient, and more resilient as well.


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The Influence of Diet on Metabolism and Hormones

Additionally what we eat has the power to alter metabolism via the endocrine pathway. Depending on the type of food consumed, it may be burned, stored as fat, or utilized in cellular regeneration. What food becomes once it is consumed will depend on the food’s composition abd what the body needs.

Macronutrients and Metabolism

Foods that are high in saturated fats and refined sugars eaten in excess will be processed into energy storage to be used later for energy output during activity. In contrast, a nutrient-dense food high in protein eaten in moderation will be used for energy conversion, tissue replacement, and rebuilding; the food is utilized to rejuvenate and replace the body’s active tissues.

Protein, carbohydrates, and fats impact hormonal responses in different ways when introduced to the digestive system. Certain amino acids in high concentrations from complete proteins can increase growth hormone production, which in turn raises metabolism.


Since hormones are made from proteins, a diet with inadequate protein intake may lack the raw materials to rebuild the body or even manufacture the hormones that initiate such actions of rejuvenation. Furthermore, ingesting adequate protein will help suppress ghrelin–the hunger hormone–and increase leptin—the satiety hormone, and maintain this balance throughout the day.

Furthermore, some studies indicate that eating a high protein diet (30% of calories) resulted in a regulated energy balance and lower hunger levels when compared to those on an adequate protein diet (10% of calories) even though energy intake remained the same. In other words, the high protein group expended more energy throughout the day.


Carbohydrates can influence insulin to a greater or lesser extent depending on the source and type of carbohydrates. Insulin is a hormone that affects storage and uptake of nutrients. Refined, simple carbohydrates enter the circulatory system rapidly from the digestive tract and quickly elicit a large release of insulin. This signals the rest of the body to pull blood sugar (glucose) from the blood. If the glucose depots (muscles and liver) are full, it will be converted to fat and stored in the adipose tissue.

Hormones Appetite & Hunger

Hormones appetite & hunger. Human endocrine system. Incretin, ghrelin, leptin and insulin

This roller coaster effect of insulin feedback in response to elevated blood glucose causes hunger mechanisms to be activated as well. When too much insulin is secreted, blood sugar levels drop too low and the hunger hormone ghrelin is released. The more insulin secreted in the presence of high blood glucose the more the body will store the energy in the cells and create a vicious cycle of eating.

Complex carbohydrates, on the other hand, take longer to process in the digestive tract and have a much slower absorption rate into the bloodstream, hampering such a roller coaster effect. Controlling insulin with diet choices makes it easier to control hunger, storage, and the food energy conversion rate.


Years ago fat was thought to be the main culprit to obesity, but now we better understand the role of fat in the diet. Science is uncovering which fats are actually of benefit to a healthy metabolism. Without dietary fat, one cannot absorb fat-soluble vitamins (A,D,E,K) that are crucial to almost every metabolic action in the body.

Also, there has been recent scientific research that indicates that certain fatty acids (CLA, GLA, omega 3’s, etc.) have hunger-busting, thermogenic, and even anabolic properties. It is not well understood how these fats perform these actions, but they are well-documented and now widely utilized for health aspects.

Balanced Nutrition for the Win

Balanced nutrition provides construction materials for replacement tissues and body systems and fuel to be converted to energy. It also provides catalysts (vitamins, minerals, trace elements, etc) for the billions of chemical reactions that are taking place all the time, and protecting the abundance of free radicals that we are in constant production and contact with from our activities and environment.

The diet-exercise-hormonal link is well established. It should also be noted that the absence of regular exercise and optimal nutritional intake is detrimental to the body and the deregulation of these hormonal pathways. Chronic inactivity and poor dietary choices can lead to premature aging and disease.

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Michele Rogers

NFPT Publisher Michele G Rogers, MA, NFPT-CPT and EBFA Barefoot Training Specialist manages and coordinates educational blogs and social media content for NFPT, as well as NFPT exam development. She’s been a personal trainer and health coach for over 20 years fueled by a lifetime passion for all things health and fitness. Her mission is to raise kinesthetic awareness and nurture a mind-body connection, helping people achieve a higher state of health and wellness. After battling and conquering chronic back pain and becoming a parent, Michele aims her training approach to emphasize fluidity of movement, corrective exercise, and pain resolution. She holds a master’s degree in Applied Health Psychology from Northern Arizona University. Follow Michele on Instagram.