By Michael Ormsbee, PhD, Florida State University
Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Many people have attributed their weight gain to a defective thyroid hormone. Fortunately, the power to affect your body composition is still in your hands. Professor Ormsbee explains.
When thyroid hormones are in the normal range, your body is perfectly able to maintain a healthy body composition with regular exercise and good eating habits. Photo by Anatomy Image / Shutterstock
What is the thyroid?
The thyroid hormones are produced by the thyroid gland in the neck. The two hormones released from the thyroid are called thyroxine or T4 and triiodothyronine (T3).
T4 is produced in larger quantities, but T3 is the more biologically active thyroid hormone in the body. In other words, T3 actually does the job.
“These unique messengers affect most body functions and affect almost every tissue in your body throughout your life,” said Professor Ormsbee. “In all honesty, it would be easier to discuss what they don’t do.”
In short, the thyroid hormones regulate body temperature and are necessary for efficient metabolism, normal growth and development, and for many other hormones to work. For example, infants and children without normal levels of thyroid and growth hormones have growth and development problems.
Because the thyroid hormones are involved in many metabolic processes, they also play a role in maintaining and increasing your resting metabolism and generating body heat in a process called thermogenesis.
Heat generation is another process that uses up energy and can affect your body composition over time. Many of the body functions that affect thyroid hormones use up energy, and we need to replenish that energy through food.
Thyroid concentrations in overweight people
Usually, after eating or burning more calories, T3 increases energy expenditure as our food is broken down and transported to different cells in the body. This can help regulate weight when thyroid hormones are in a normal range. Hence, we need normal T3 levels to be healthy in many ways.
Take, for example, a study in which obese people reportedly had higher levels of T3 with increased energy expenditure and increased metabolism. This correlation may sound strange to you as T3 increases calorie consumption. However, this increase in T3 in these obese individuals can be an adaptive response to prevent further weight gain, and T3 can be increased to reduce the amount of energy stored as fat.
On the other hand, T3 has been shown to be very low in underweight individuals and while starving, and this is likely your body’s attempt to slow down your metabolism and conserve energy. These adjustments appear to be in place to reduce fat mass in the overweight and to maintain or increase fat in the underweight to help people maintain healthy body weights.
Unfortunately, some people experience chronically low levels of T3 and T4 in what is known as hypothyroidism. Weight gain is likely in these circumstances. If the opposite occurs and T3 and T4 are chronically high, it is called hyperthyroidism and would likely result in weight loss.
Importance of drugs
Keep in mind that in otherwise healthy individuals taking synthetic thyroid hormones, your doctor has likely brought your blood levels of T3 and T4 to normal ranges. So if you take medication for diagnosed hypothyroidism or low thyroid function, your thyroid problem will no longer be responsible for weight or fat gain.
Your levels are normal due to the thyroid medication prescribed by your doctor.
“As one endocrinologist I know said,” The rate of obesity does not match the rate of thyroid disease diagnoses, “said Professor Ormsbee.” Your body is perfectly capable of maintaining healthy body composition with smart exercise and quality nutrition for so long Your thyroid levels are regulated. “
Influences of body composition
Hormones, gender, and age all affect your body composition. We have known for some time that men naturally have more muscle mass than women, while women tend to have more total body fat.
This is often explained by the location of body fat and women’s unique reproductive function needs. The higher fat levels and lower muscle levels in women typically mean that women have metabolic rates that are about 5% to 10% lower than men of the same size and weight because the muscle mass is more metabolically active. In addition, women are 5 to 8 times more likely than men to develop hypothyroidism, which, if left untreated, can lead to weight gain.
In a scientific article on gender differences in body composition and insulin resistance, the authors of this review found that men who tend to have more fat around their internal organs are more insulin resistant than women who tend to have their fat around their arms and organs Save legs.
Therefore, the health consequences of excess fat depend not only on the presence of body fat, but also on where that fat is located. However, as we age, our hormones also change, which affects the storage of muscle tissue and fat.
For example, postmenopausal women gain more abdominal fat mass due to the decrease in estrogen levels. It has also been shown that postmenopausal women are less efficient at burning fat both at rest and during exercise.
The prevalence of hypothyroidism or underactive thyroid also increases with age and affects about 9% of men and women over 60 years of age. This can have an impact on weight gain in later years since, as you know, a decrease in thyroid hormones slows your metabolism if not treated with medication.
In addition, muscle mass and strength decrease with age, which is due to a gradual loss of skeletal muscle after age 30 – around 5% to 10% per decade.
It’s not all doom and gloom, however – these massive body composition changes only occur when you choose not to exercise or eat properly. Indeed, other evidence shows excellent muscle mass quality and function in lifelong exercisers and athletes.
This article was edited by Kate Findley, author for The Great Courses Daily, and proofread by Angela Shoemaker, proofreader and editor for The Great Courses Daily.
Michael Ormsbee is Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Exercise Science and Medicine at Florida State University’s College of Human Sciences. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.