How Hormones Influence Your Ability To Lose Fat & Increase Muscle

Hormones are one of the most important factors affecting your ability to lose fat and increase muscle. They affect all aspects of human function, determining how the body responds to physical and psychological stress. They enable world champion athletic performances, govern metabolic rate, and tell us when we’re hungry.

But hormones don’t exist in a vacuum. No single hormone can be classified as good or bad. Instead, hormone levels are constantly in flux, influencing each other as well as impacting different systems in the body.

It’s when hormones get out of balance and there is too much or too little of a hormone at certain times that causes problems. This makes understanding hormones and their interaction with your brain inherently complicated.

This article solves that, giving you an in-depth rundown on what hormones do and how to balance them.

#1: Cortisol

What it does: Increases in response to both physical and psychological stress in order to free energy stores to be burned. Suppresses the immune system, preserving the most vital functions to get you through stressful times.

Body composition effects: When balanced, cortisol can be beneficial for body composition by triggering fat burning. For example, cortisol increases during exercise to increase the amount of fat your body uses, while sparing glycogen.

However, when cortisol levels are chronically high, muscle loss and fat gain often occur. If you are in an energy surplus and experience intense stress throughout the day, high cortisol in the presence of insulin makes the body store fat.

On the other hand, during starvation or severe calorie restriction, chronically high cortisol leads to muscle loss and suppressed immune function.

How it responds to exercise: When you start working out, cortisol, and energizing hormones like the catecholamines and growth hormone are released in order to free fat stores so the body can burn them for energy. Researchers also think the workout spike in cortisol may play a role in tissue recovery and repair after intense exercise.

Endurance exercise tends to lead to larger cortisol elevations than strength and power training. Repeated bouts of intense, long-duration training lead to adrenal gland enlargement due to high cortisol output.

How it responds to diet: There are two main concerns in balancing cortisol with diet:

First, the presence of insulin changes how cortisol behaves. When blood sugar is elevated due to a high-carb meal, there will be a large insulin release, which increases a primary fat storing enzyme called lipoprotein lipase (LPL).

Insulin blocks the action of another major fat burning enzyme, hormone sensitive lipase (HSL). The combination oh high insulin and cortisol is the perfect environment for gaining body fat.

Second, a calorie surplus along with high cortisol levels will lead to fat gain. For example, if you go long periods without eating, cortisol will increase. If you then eat a huge meal, taking in more calories than you need, insulin and cortisol will be high, leading any excess energy to be deposited as fat.

#2: Insulin

What it does: A storage hormone that regulates glucose entry into fat and muscle cells.

After eating a meal when blood glucose levels rise, any glucose not immediately used for energy either stores as muscle glycogen or is stored as fat.

Insulin also triggers enzyme activity that facilitates protein synthesis, which is useful for building muscle and repairing tissue.

Body composition effects

Stores any excess energy as body fat. Triggers protein synthesis and is involved in muscle building. However, studies show that an insulin spike from a high-carb meal is not technically necessary to maximally trigger protein synthesis.

How it responds to exercise

Insulin stays close to resting levels during exercise so that you avoid blood glucose levels from plummeting as energy needs are ramped up.

How it responds to diet

Insulin is elevated in response to carb intake, with release corresponding to the increase in blood glucose levels. This means high-carb, fast digesting foods will elevate insulin much more than lower carb, slower digesting foods.

Protein also elevates insulin, but the metabolic effect is different than when you eat carbs. For example, whey protein leads to a large, unexplained increase in insulin that is not expected based on its amino acid profile. This is not detrimental to metabolic health and taking whey protein over the long-term can improve glucose tolerance.

If your goal is fat loss, it’s important to manage insulin and avoid large, repeated spikes over the course of the day because high insulin = perfect fat storing environment.

#3: Testosterone

What it does: Facilitates protein synthesis and promotes growth hormone and IGF-1 release. Leads to adaptations that enhance muscle’s ability to produce force.

Body composition effects: Promotes fat burning and the development of lean mass in trained muscle. The greatest effect occurs during large, sustained elevations in testosterone levels, such as during puberty or due to the use of anabolic steroids.

How it responds to exercise: High-intensity exercise such as sprints and traditional weight training tend to increase testosterone in both men and women.

Endurance exercise tends to depress testosterone production in men. It generally increases testosterone release slightly in women. However, other reproductive hormones such as FSH and LH are typically reduced in female endurance athletes, which can lead to menstrual irregularities.

How it responds to diet: Testosterone is produced in the body out of cholesterol, which you get from dietary fat. Studies show that men with a higher fat intake have significantly higher testosterone than those who restrict fat. For instance, in one study, men who switched to a low-fat, higher carb diet resulted in a 12 percent drop in testosterone and other androgen hormones.

Carb intake also affects testosterone production. In response to a blood sugar spike from high-carb foods, testosterone is temporarily reduced by 25 percent.

That’s not the whole story: Chronically, carb intake is important for testosterone production and low-carb, high-protein diets can lead to depressed testosterone levels. Therefore, vegetables, fruit, and other whole carbs from beans and select grains can be beneficial for healthy testosterone levels. Diets high in fast-digesting and refined carbs are contraindicated.

#4: Growth Hormone

What it does: Facilitates protein synthesis, slows carbohydrate breakdown, and initiates fat burning.

Body composition effects: Triggers muscle building and stronger connective tissue. Improves fat loss.

How it responds to exercise

GH release responds to how strenuous you train. This is why sprint training and maximal effort workouts are recommended for elevating GH and reaping its fat burning, muscle building effects. It’s also the reason that high lactate levels are associated with GH release—lactate is produced at high intensities in which inadequate oxygen is present.

How it responds to diet: GH is an insulin antagonist, which has led to the incorrect assumption that low-carb diets lead to higher GH levels. For all practical purposes, you don’t need to worry about modifying diet in order to specifically alter GH levels for two reasons.

First, transient changes in GH probably don’t have much affect on body composition.

Second, it’s only true that low blood sugar triggers GH release after hyperglycemia and high insulin. Basically, after subjects consume a large dose of glucose to spike insulin, they experience a reactive drop in blood sugar and there is a large “rebound” GH secretion.

#5: Thyroid Hormone

What it does: Regulates metabolic rate by affecting enzyme activity, body temperature, and influencing energy levels. Also involved in heart function and central nervous activation.

Body composition effects: Thyroid hormone must be balanced for sustainable fat loss because it regulates metabolic rate and body temperature.

One reason people often plateau when losing body fat is that thyroid hormones are reduced, lowering body temperature so that the body burns fewer calories. Low thyroid hormone also reduces protein synthesis and causes sluggishness and fatigue.

Too much thyroid hormone and you get an elevated resting metabolic rate that leads to rapid fat loss and muscle wasting due to increased protein catabolism. People with hyperthyroidism have a hard time sustaining body weight, which might sound favorable in a fat-loss obsessed nation, but it drastically reduces quality of life, often leading to insomnia, elevated heart rate, and irritability.

How it responds to exercise: In response to intense exercise, thyroid hormone increases, particularly at intensities above the lactate threshold. For practical purposes, it’s not something you need to worry about as long as your levels are within normal range.

How it responds to diet: Calorie restriction and very low-carb diets lead to reduced thyroid. This is one reason that long-term, very low-carb diets generally aren’t tolerated very well. It’s also why carb cycling can be useful when living a lower carb lifestyle.

#6: Catecholamines

What they do: Commonly called adrenaline hormones, the catecholamines are epinephrine and norepinephrine, and they stimulate the central nervous system. They affect the heart, blood vessels, and elevate energy metabolism.

Body composition effects: Stimulate energy metabolism as physical activity increases, initiating fat burning both in fat tissue and active muscles.

How they respond to exercise: Catecholamine release is most closely related to exercise intensity. In a study of male cyclists, norepinephrine increased linearly as intensity that exceeds 50 percent of VO2 max, whereas epinephrine remained unchanged until intensity exceeded the 75 percent level.

Sprint and power athletes show higher elevations of the catecholamines than endurance athletes, which is related to the higher anaerobic contribution to energy supply during these activities.

How they respond to diet: The catecholamines typically increase when restricting calories in order to simulate fat burning to keep you going when incoming energy supplies are low. This is one reason why intermittent or alternate day fasting can help with fat loss and weight maintenance.

One concern is that over the long term, fasting can lead to elevated sympathetic nervous system activation (known as the fight or flight system) and may inhibit sleep.