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Hormones and Metabolism

Blog #5 in Metabolism Series

Your hormones play an important role in metabolism. Different hormones in the body are associated with either anabolism (building up) or catabolism (breaking down) and they help to regulate our metabolism. Now before we talk about a few key hormones involved in the regulation of metabolism, we need to first figure out what hormones are.

What Are Hormones?

Hormones are your body's chemical messengers. Their role is to provide an internal communication system between cells located in distant parts of the body. Endocrine glands, which are special groups of cells, make hormones. The major endocrine glands are the pituitary, pineal, thymus, thyroid, adrenal glands, and pancreas. In addition, men produce hormones in their testes and women produce them in their ovaries.

In response to a signal from the brain, hormones are secreted directly into the blood by the glands that produce and store them. While all cells are exposed to hormones circulating in the bloodstream, not all cells react to the hormone. Only a hormone's "target" cells, which have receptors for that hormone, will respond to its signal. When the hormone binds to its receptor (either on the cell’s surface or it crosses the plasma membrane and acts upon the receptor inside the cell), it causes a biological response within the cell.

The endocrine system is responsible for regulating a range of bodily functions through the release of hormones (see Table 1). We have both anabolic hormones and catabolic hormones. Anabolic hormones build up simpler molecules into complex molecules and use energy while catabolic hormones break down complex molecules into simpler ones and release energy. Hormonal balance, or the balance between anabolic and catabolic hormone production, is necessary for keeping everything functioning properly inside the body. When your hormones get “out of whack,” there are several unwanted consequences that can occur including your metabolism. Let’s dive into a few of these hormones to see how they may affect metabolism.

Let’s start with insulin, an anabolic hormone. Insulin is produced in the pancreas and is a critical hormone in carbohydrate, fat, and protein metabolism. For example, insulin is the key that unlocks the door to allow glucose to enter the cell to be used as energy. So how does insulin affect our metabolism? Well, that comes down to insulin resistance which is defined as a decrease in tissue response to insulin. When your cells are resistance to insulin, meaning they no longer allow it to open the door, then glucose and insulin levels increase within the bloodstream. This promotes storage of glucose in the liver and muscle, as well as fat storage. Abdominal or central adiposity, and in particular visceral adipose tissue (the fat that is deep inside your belly that wraps around your organs), is strongly related to insulin resistance. When we increase central obesity through poor nutrition and/or lack of physical activity, we increase insulin resistance. Insulin resistance increases central obesity. It is a chicken and egg situation, we may not always know which one came first. The good news is that exercise, aerobic and/or resistance training, increases insulin sensitivity which can helps us to decrease our fat mass.

Another hormone of importance in metabolism is estrogen. Estrogen’s job is to regulate the menstrual cycle, maintain pregnancy, and develop female sex characteristics. In men, proper estradiol levels help with bone maintenance, nitric oxide production, and brain function. Estrogen is anabolic in nature as it requires energy to work. For example, in the ovaries we need estrogen to produce egg follicles. Females mainly produce estrogen in the ovaries and smaller amounts are produced by the adrenal gland and fat cells. In men, the testes produce only ~20% of circulating estrogens, with the remainder from local production by adipose, brain, skin, and bone, which convert testosterone (T) to estrogen through aromatase actions. As we grow older, estrogen levels decline in both males and females. Studies show that estrogen deficiency triggers an increase in food intake, a decrease in spontaneous physical activity (fidgeting or changing your posture), and a suppression of the metabolic rate - all which contribute to weight gain. This makes it harder to lose weight during menopause and beyond BUT, research consistently shows that exercise, (endurance, resistance or a combination of the two) can improve body composition even during estrogen deficiency.

Let’s look at one more anabolic hormone, testosterone. This hormone is produced by the ovaries and testes as well as the adrenal glands. We mostly think of it being responsible for male sex characteristics such as facial hair and a muscular build, but in both genders, it promotes healthy bones and cognitive function, increases muscle mass and maintains sex drive. Aging beyond 35-40 years is associated with a 1-3% decline per year in circulating testosterone concentration in men; this decline eventually results in the condition known as andropause. In women, circulating testosterone concentration also gradually declines until menopause, after which a drastic reduction is found. As levels of testosterone drop, we may begin to experience lack of sexual desire, low mood, low energy or fatigue and impaired focus and concentration and we can experience an increased risk of bone loss…and you guess it… an increase in fat mass - especially around the middle. Once again, exercise will help to improve body composition even with low testosterone.

Let’s talk about one more hormone, cortisol. Cortisol gets a lot of attention and it is known as the stress hormone. It is released from the adrenal gland in response to stress and its main role is to increase blood glucose levels by gluconeogenesis (breaking down fats and proteins), making it a catabolic hormone. Blood levels of cortisol vary throughout the day, but generally are higher in the morning when we wake up, and then fall throughout the day. During times of increased stress (physical or psychological), cortisol, in addition to epinephrine, is released from your adrenal glands. This triggers an increase in heart rate and energy levels, preparing your body for a potentially harmful situation. While this response is normal, continued elevations in cortisol can lead to negative side effects. We see elevations in cortisol levels beginning in the third decade of life as cortisol levels in women and men gradually increase with age. We also see chronic elevation of cortisol in individuals who experience both real and perceived stress on a daily basis. Prolonged elevated levels of cortisol have been found to lead to an increase in appetite especially for sweet, salty and fatty foods, an increase in weight and an increase in central obesity. The biggest thing you can do to combat high level of cortisol are to engage in activities that reduce your level of stress such as mediation, mind body exercise, or deep breathing.

The bottom line is YES, your hormones can affect your metabolism and weight. Working with your physician to balance hormones and choosing the right exercise design to minimize hormonal issues will help to lead you in the right direction.

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