We hear the word "hormones" get thrown around constantly and it seems that everyone agrees–not only are hormones important but having balanced hormones is crucial for overall health.
Before we talk about disease processes and the repercussions of hormone imbalance, I would like to discuss the basics. What exactly is a “hormone”? Hormones are signaling molecules. They are the words our body uses to communicate within itself. Hormones are secreted by different glands in the body.
For the most part, once a hormone is secreted by a gland, it travels by the circulatory system. Once at its destination, the hormone binds to a cell receptor and triggers a pathway cascade that will regulate a certain function. These functions include digestion, hunger, fertility, metabolism, sleep, stress, growth, perception, mood, and many other processes.
The gland system responsible for hormone production is known as the endocrine system. The endocrine system is made of multiple feedback loops that regulate bodily functions. Most of them function based on a principle known as negative feedback.
There is a stimulus–a hormone gets produced–higher concentrations of this hormone notify the “origin” that there is too much being produced and the production is stopped. Let's take a look at a key player, the thyroid hormone.
The thyroid axis is responsible for metabolism. It involves the communication between the hypothalamus (a link of the nervous system to the pituitary gland), the pituitary gland, and the thyroid gland. The thyroid gland gets a lot of attention from the weight loss community.
You might have heard people attributing their weight gain to a “slow metabolism” or a “sluggish thyroid.” This is because one of the primary functions of the thyroid gland is to maintain your basal metabolic rate (BMR)—the bare minimum calorie requirement for you to stay alive. These calories are required for organ function, generating body heat, growth, development, etc.
Trainer Antonella Kahler from Toronto, Canada
So then, what is a hypo/hyperthyroid? A “hypo” or “hyper” thyroid refers to the thyroid’s abilities to release appropriate hormones to upregulate or downregulate metabolism. So it would seem logical that a “hypothyroid” would crash our metabolism and make weight loss impossible while a “hyperthyroid” would keep us effortlessly slim
This is not the case. In fact, the role of thyroid hormones in diet-induced weight loss is largely unknown. For example, certain irregular thyroid hormone profiles are found in obese populations, however, these seem to be an effect of obesity and not the cause.1
Symptoms of a “sluggish” thyroid include fatigue, feeling cold, trouble concentrating, hair loss, weight gain, and water retention. If you experience any of these symptoms, get a proper diagnosis from a qualified endocrinologist.
Never self-diagnose or self-treat. The relationship between the thyroid gland, BMR, and overall body weight is extremely complex and still not completely understood. Having a slightly slower or faster metabolism does not really impact weight because it also affects appetite.
People with a slower metabolism generally want to eat slightly less, while those with a faster metabolism have more ravenous appetites. So, with all other things being equal, it does not seem that BMR fluctuations are to blame for weight gain or weight loss in a healthy individual.
Even in a medically "slow hypothyroid” person, the decrease in metabolism is not very dramatic. Medically underactive thyroids can only cause slight weight alterations, most of which are due to excess salt and water. In severe cases of hypothyroid, one would only see a general increase of 10lbs of body weight, which tends to be resolved with appropriate medication. Any weight gain in excess of that amount is extremely unlikely to be solely due to the thyroid.2
A Healthy Thyroid
Just because we have a “healthy” thyroid does not mean that we can’t directly affect it and alter its function. The fastest way to “crash” your thyroid is through excessive dieting.
When we diet, the body undergoes a multitude of processes known as metabolic adaptations.
This is a natural survival mechanism. If your body senses that you are in a prolonged calorie deficit, it will begin to tweak its energy expenditure patterns. You will slowly go into a quasi-hypothyroid state. You might remember from some of your longer diets feeling cold and sluggish. These are symptoms similar to traditional hypothyroid.
The difference is that in a healthy individual, this process is completely reversible. Your metabolism did not suffer damage and “starvation mode” is a myth. Starvation studies prove that if the calorie intake is low enough, regardless of the state of the thyroid, an individual will still lose weight.3
Starvation mode is a myth. However, the metabolism is capable of adapting to a lower calorie intake. This means if there is rebound weight gain; it tends to be more excessive than if the individual never dieted.4 This is partially the reason why yo-yo diets seem to overshoot the individual above their original weight.
Nevertheless, the metabolism is capable of adapting back to its original state. This is where reverse dieting, recovery diets, and dieting breaks become a crucial part of lifelong success.5
The easiest way to prevent metabolic adaptation is to have a smaller calorie increase. There really is never any logical reason to push hard for fast weight loss. We might have a trip or a special event in mind, but if we are pushing for rapid weight loss we need to remember the side effects.
When dropping calories, we need to aim for the minimum decrease possible while still seeing an effect. It should at maximum be a 20% reduction of maintenance calories. You must take diet breaks to give your metabolism a chance to recover. You have to take scheduled diet breaks. A 1-2 day “re-feed” is not enough–that little boost in metabolism is short lived.
Re-feed days and calorie cycling are more for a mental benefit than to have a protective effect over metabolism. They help clients keep adherent. In order to have a good “recovery period” it is recommended that every 8-12 weeks of a calorie deficit, you take a 2-4 week diet break.
During this time, you are bringing your calories up to maintenance. Don’t forget that your maintenance at this stage will not be the same as when you started, primarily because of your change in body weight. Your maintenance calories are (on average) your body weight in lbs x15.
You can either jump to your new predicted maintenance immediately or boost your calories slowly (by weekly increasing by 150-200 calories for your daily calories). Once you are at maintenance, you will begin your 2-week break.
How Many Maintenance Calories Do I Need?
If you eating your predicted maintenance calories but are steadily gaining weight, your maintenance is below your predicted value. If this occurs, it is likely that you experienced a degree of metabolic adaptation that needs an intervention—a reverse diet. To heal your metabolism, you must first find your new maintenance calories (unfortunately purely by trial and error).
Once this is accomplished, you are to very slowly increase your calorie intake by increasing your carbs and fats. Most people start at a 50-100cal/week increase. This type of slow, gradual adjustment allows your metabolism to repair itself and bring you back to your original maintenance. It is possible to achieve the same effect with a faster adjustment, however, the faster you “reverse,” the higher the likelihood that there will be more fat gain in the process.
The speed at which you need to reverse diet completely depends on your individual goals. If you are a stage-lean competitor who is in need of boosting their body fat, a faster reverse diet is more optimal. However, if you are an individual struggling to lose weight consistently and would not like to put on additional body fat, slower might be better.6
Is Keto Bad for My Thyroid?
In a ketogenic diet, you must drop your carbohydrate low enough (usually sub 25g), so that the body starts to use fat, rather than carbohydrate, as its primary energy source. As the liver breaks down fats for energy production, it releases ketones–hence the term “ketogenic diet.”
The ketogenic diet is excellent at controlling hunger and cravings, but does it damage the thyroid? Some studies say yes if you eat a lot of omega 6 fats. What are some examples of omega-6? These include canola oil, grapeseed oil, corn oil, soybean oil, walnut oil, and multiple other sources. It does seem that omega 6s have an impact on the thyroid.7
Other keto studies show an effect on the thyroid, but they also had the participants go on extremely low-calorie diets As we have discussed, reducing calories affects the thyroid. Studies also found that after a period of “refeeding”, the thyroid levels stabilized.9
Therefore, the research on whether keto specifically affects the thyroid gland is inconclusive. If you are succeeding on a ketogenic diet, proceed with caution. If you are a diagnosed hypothyroid individual, you may want to choose an alternate diet method or discuss this further with your endocrinologist.
Takeaway for a Healthy Thyroid
- Have a diet that includes chicken, shellfish, Brazil nuts, iodized salt, and eggs. These foods contain iodine, zinc, and selenium—nutrients necessary for a healthy thyroid.
- Cook your sweet potatoes, Brussels sprouts, cauliflower, and spinach. These foods contain goitrogens (compounds that interfere with iodine uptake). Cooking deactivates them.10
- Take diet breaks. Give your metabolism a chance to recover by taking a diet break for 2-4 weeks every 12-week diet cycle.
- Be careful with keto. Pay close attention to your body when doing a ketogenic diet.
1. Reinihr, T. (2010). Obesity and Thyroid Function. Mol Cell Endocrinol. 2010 Mar 25;316(2):165-71. doi: 10.1016/j.mce.2009.06.005. Epub 2009 Jun 18
2. American Thyroid Association. (2018). Thyroid and Weight.
3. Leah M. Kalm and Richard D. Semba, "They Starved So That Others Be Better Fed: Remembering Ancel Keys and the Minnesota Experiment," Journal of Nutrition, Vol. 135, June 2005, 1347–1352.
4. Maclean, P.S., et al., Biology’s response to dieting: the impetus for weight regain. Am J Physiol Regul Integr Comp Physiol, 2011. 301(3): p. R581-600.
5. Knuth, N.D., et al., Metabolic adaptation following massive weight loss is related to the degree of energy imbalance and changes in circulating leptin. Obesity (Silver Spring), 2014. 22(12): p. 2563-9.
6. Trexler, E.T., A.E. Smith-Ryan, and L.E. Norton, Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr, 2014. 11(1): p.7.
7. Reed, EB and Traver, H. The influence of diet on the lipogenic response to thyroxine in rat liver. Life Sci. 1975 Dec 15;17(12):1785-97.
8. Spaulding SW, Chopra IJ, Sherwin RS, Lyall SS. Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man. J Clin Endocrinol Metab. 1976 Jan;42(1):197-200.
9. Bisschop PH, Sauerwein HP, Endert E, Romijn JA. Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men. Clin Endocrinol (Oxf). 2001 Jan;54(1):75-80.
10. Rao PS1, Lakshmy R.Role of goitrogens in iodine deficiency disorders & brain development. Indian J Med Res. 1995 Nov;102:223-6.