Intermittent fasting is a hot topic in the diet and nutrition world. There are many books, blogs, celebrities and even apps touting the many health benefits of this pattern of energy consumption. The question is whether there is sufficient clinical research to supports these claims. Intermittent fasting has been a part of religious practices for centuries. Christian, Muslim, Buddhist, Hindu and Jewish populations all perform intermittent fasting at different times throughout the year. Clinical studies on intermittent fasting are still quite limited and what we do know comes mostly from: animal studies, a handful of human trials with small sample
By Dr. Sarah Zadek ND
The inability to lose weight from diet and exercise alone can be extremely frustrating. There are many factors that affect weight management, and for those who struggle with this it may be worth investigating other causes of this “stubborn metabolism.” One such cause is the functioning of the thyroid gland and its respective hormones. Thyroid hormones play crucial roles in how the body uses energy and regulates appetite. Additionally, fat cells, also called adipose tissue, contains their own messengers and hormones that affect energy stores and usage. The interaction between these cells, their messengers and thyroid hormones are major factors that contribute to weight management.
Thyroid hormones act directly and indirectly on metabolic cycles. As such, they help decide how and when cellular energy is used. Because of this relationship, it’s been theorized that there is a direct relationship between obesity and thyroid function. An overactive thyroid, hyperthyroidism, often results in weight loss, whereas an under-functioning thyroid and low levels of thyroid hormone (hypothyroidism), can lead to weight gain and/or an inability to lose weight.
What are thyroid hormones?
Your doctor may have told you that your “thyroid levels” are too high and they want to prescribe a thyroid hormone. Your doc is referring to your “TSH” – your thyroid stimulating hormone level. This is a hormone that tells your thyroid gland to produce and secrete a thyroid hormone called thyroxine. Thyroxine (also referred to as T4) turns into the active form of thyroid hormone referred to as T3. When TSH levels are found too high it means that your body is sending out a signal to the thyroid gland and the signal is not registering. The brain keeps sending out more signal waiting for a response, but without a response, more TSH is sent out, resulting in higher than normal levels. When this happens, your doctor will often prescribe T4 in a form called levothyroxine.
T3 hormone, temperature and metabolism
One of the roles of the active thyroid hormone T3 is to control our basal metabolic rate by exerting heat-generating activity. This explains why one of the symptoms of hypothyroidism is feeling cold. In one animal study, mice without thyroid receptors had lower metabolic rates, body temperature and were more intolerant to cold temperatures.
The link between T3 and metabolism has been investigated for decades. We’ve found that when lean individuals overeat, the rate of T3 production significantly increases. However, when calories are restricted in both lean and obese subjects researchers have reported that T3 decreases, which will slow down metabolism in the long run.
So why can’t we just take T3 for weight loss? Because it doesn’t always work, especially in patients who have normal thyroid levels. A meta-analysis reported that although patients given T3 had reduced levels of TSH, only 20% of patients actually had significant weight loss. The thyroid is not the only regulating hormone here.
Thyroid and fat tissue
Leptin is a hormone found in adipose (fat) cells and is another controlling factor in weight management. Leptin helps control food intake and energy expenditure. In general, adipose tissue increases leptin levels, which then increases TSH.
As of 2014, 18 studies have shown a positive correlation between adiposity and TSH levels. However, it should be noted that these studies looked at correlations, and that other factors such as insulin sensitivity and diet weren’t always taken into consideration. What’s important to note is that although it’s been confirmed that a high-normal TSH level is associated with a high body-mass index (BMI), it’s not clear whether the increased TSH levels are a consequence of being overweight or if it causes increased body weight.
Natural treatments for thyroid-related weight management
The herb Coleus forskohlii has demonstrated the ability to increase the production and release of thyroid hormones. Several studies have reported the potential of the herb C. forskohlli to help with weight management. One study found that treatment, combined with a hypocaloric diet, led to significantly reduced hip and waist circumference, an increase in HDL cholesterol (the “good” cholesterol), and improvements in insulin resistance.
Another promising treatment is the combination of zinc and selenium. Both are important elements involved in the metabolism of thyroid hormones. One study looked at the effect that supplementation with zinc and selenium had on thyroid function in overweight women with hypothyroidism. Women who were given zinc and selenium together, or zinc on its own both had significantly increased levels of the active T3 hormone. The zinc and selenium treatment also led to significantly lower TSH levels.
Hypothyroidism and sluggish thyroid function (elevated TSH levels) are associated with weight gain. The continuous interaction between the thyroid gland and fat tissue help to control energy stores and usage. Changes in thyroid functioning can affect this dynamic, though there are many factors involved in weight management. Dietary changes should be incorporated into any treatment plan. Other considerations include herbs such as Coleus forskohlli and elements such as zinc and selenium.
Joshi SR. Thyro-weight: unlocking the link between thyroid disorders and weight. J Assoc Physicians India. 2018; 66(3): 75-8
Loftus HL, et al. Coleus forskohlii extract supplementation in conjunction with a hypo caloric diet reduces the risk factors of metabolic syndrome in overweight and obese subjects: a randomized controlled trial. Nutrients. 2015; 7(11): 9508-22
Mahmoodianfard S, et al. Effects of zinc and selenium supplementation on thyroid function in overweight and obese hypothyroid female patients: a randomized double-blind controlled trial.
Santini F, et al. Mechanisms in endocrinology: the crosstalk between thyroid gland and adipose tissue: signal integration in health and disease. Eur J Endocrinol. 2014; 171(4):R137-52