Increasing prevalence of overweight people is a major concern globally; and in the United States, nearly one third of adults were classified as obese at the end of the 20th century. But minimal data has been presented regarding an association between variations in thyroid function seen in the general population and body weight.
The Thyroid and Body Weight Connection
The thyroid provides important bodily functions. Because it stimulates the production of cellular energy, production of all other hormones will be negatively impacted when thyroid hormone levels are less than optimal. Every aspect of health is affected by low thyroid function.
The association between serum thyroid hormones and body mass index (BMI) or obesity was examined in a cross-sectional population study (The DanThyr Study) of 4,082 eligible participants. The results suggested that thyroid function (also within the normal range) could be one of several factors acting in concert to determine body weight in a population. Even slightly elevated serum TSH levels are associated with an increase in the occurrence of obesity. Consequently, suboptimal "normal" thyroid levels can result in weight gain, obesity and inability to lose weight and optimizing thyroid levels can be considered beneficial and possibly necessary for the maintenance of normal weight.
The hidden causes of hypothyroidism are multiple. But one of them is mostly overlooked: studies show that if you chronically diet or "over exercise" your body may turn on you and reduce your metabolism by suppressing thyroid levels. "Chronically dieting" means choosing the wrong diets for your metabolism, over and over again and depriving it from the very nutrients it actually needs to stay healthy. Like with dieting, "over exercise" means forcing your body into strenuous exercise routines, which are not suitable for your existent health conditions and push your body even more into imbalance. Simply put, "one size just doesn't fit all."
The body normally produces an inactive thyroid hormone called T4, which is then converted to T3. The T3 is the active substance that is responsible for your body's metabolism. When it is low or suboptimal, your metabolism is low. When it is high, your metabolism is high.
Humans are very successful as a species because we can store energy (fat) efficiently and have multiple ways to store this energy. Thus, for long-term success physicians must look at the metabolic and endocrinological factors leading to weight gain and not assume it is a matter of will-power to eat less and exercise more.
A reduced basal metabolic rate is a consistent finding in those who chronically diet, with many such individuals having 20-40% lower metabolism than expected for their BMI. With such a reduced metabolism, you must eat 500-1000 less calories per day or burn that many calories to just stay even and not gain weight. While diet and exercise are important components of successful weight loss, they will certainly fail to achieve long-term success if metabolic abnormalities are not addressed.
Listen to a webinar of Dr. Kent Holtorf with Mary Shomon talking in-depth on the various reasons why many cannot lose weight in spite of diet and exercise and see the relationship between thyroid and obesity.
Understanding Local Control of Thyroid Hormones: (Deiodinases Function and Activity)