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Weight gain and fluctuations are a very common symptom of an underactive thyroid or hypothyroidism. However, many thyroid patients are taking to dieting, i.e. cutting out calories or certain food groups, in an attempt to shift pounds, may be making their hypothyroidism worse.
Are Low-Calorie Diets Making Us Worse?
For many thyroid patients who go on low-calorie and fad diets, they just don’t seem to work. People either don’t lose weight, carry on gaining weight despite dieting, or lose the weight but soon gain it back, often with a few additional pounds on top to boot.
I’ve heard from literally thousands of thyroid patients who ask why this happens. And it’s quite simply because hypothyroidism is so involved with our metabolism and energy levels.
Dieting Reduces Active Hormone Levels
This scenario of being unable to lose weight and keep it off becomes even more common when someone repeatedly goes on low-calorie diets, fads, or struggles with yo-yo dieting (repeated loss and gain of weight).
What many thyroid patients don’t know is that chronic dieting can reduce Free T3 levels, the active thyroid hormone, causing the metabolism to slow down even further and weight loss to become even more difficult as time goes on. T3 is crucial for the functioning of every cell and function of the body, from brain function to bowel movements and energy. And the metabolism is in charge of our energy levels, production, body heat and thus, weight loss and gain.
Thyroid hormones play an important role in metabolic function. Whilst we need enough T3 to feel well and have a body that functions properly, Reverse T3, an inactive form of T3, is an issue. Too much Reverse T3 blocks the cell receptors for thyroid hormones, thus blocking the effect of the all important T3. If a patient has too much Reverse T3 in ratio to Free T3, then they are hypothyroid at a cellular level, which results in a reduced metabolic rate.
Studies have found that dieting can reduce metabolic function hugely. One particular study published in the American Journal of Physiology, Endocrinology and Metabolism, showed that even twenty-five days of restricting calories can result in a significant reduction of T3, due to less T4 converting to the T3. It resulted in a 50% reduction in T3, which, as already explained, affects everything including your metabolic function.
Cortisol and Weight
The adrenal glands produce a range of hormones, however the one we’re looking at right now is cortisol. If your adrenals detect that you are under stress, they produce more of this ‘stress hormone’.
One type of stress? Restricting calories.
When you restrict calories, increased cortisol starts signalling that food is scarce and to slow down your metabolism as a result, storing fat as its survival mechanism.
If you ignore these signals from your adrenals, and carry on pursuing a low calorie diet, you are reaffirming to your body that food is indeed scarce and therefore it will keep up this survival mechanism.
Why Attempts To Lose Weight and Keep it Off Often Fail
Unless the effects of chronic dieting are addressed, such as low T3 levels, excess Reverse T3 and even adrenal dysfunction (which often drives Reverse T3 levels up), attempts to lose weight and keep it off will often fail.
Where a lot of thyroid patients struggle is convincing their doctor to test Free T3 and Reverse T3 levels in the first place, which are very important. Addressing any non-optimal levels in these can help a lot of thyroid patients to not only lose weight if they wish, but also shift many other thyroid symptoms including fatigue, poor stamina, muscle aches and more.
Your Set Point
There is also something called your weight ‘set point’ which you should take in to consideration. Your ‘set point’ is the brain’s target weight for you. It is therefore individual and thyroid patients can have an even further altered set point. 
Just as the body aims to maintain a normal body temperature, it also works to maintain a body weight that is physiologically comfortable. The ‘set point’ is maintained by the hypothalamus and is often genetically influenced, however, a number of things can cause this ‘set point’ to change, including making it a higher or lower number. Chronic dieting is the main cause for an abnormal ‘set point’, whereby it can result in slower metabolism as explained previously.
Ways to address this can include reaching optimal thyroid levels, a more consistent diet and calorie intake (no more yo-yoing, fad diets or calorie restrictions), consistent exercise (no more overexercising followed by needing to heavily rest due to the damage going too far does) and managing your Hashimoto’s.
Your Weight Isn’t The Sole Indicator of Your Health
When it comes to weight gain and weight fluctuations with hypothyroidism, I do understand the frustrations. My weight has fluctuated quite a lot with hypothyroidism and what I’ve learnt in my bid to try and lose weight with frequent yo-yo dieting and calorie restrictions, is that my physical health is so much more important than how I look in the mirror, or my weight alone. Often, if we focus on feeling physically well, such as reaching optimal thyroid levels, vitamin levels and ensure good adrenal health, our bodies tend to shed any extra pounds that it doesn’t need anyway.
I just want thyroid patients to be aware that often, dieting and calorie restrictions place extra stress upon the body, that it just doesn’t need when it’s already balancing chronic illnesses and hormone imbalances such as hypothyroidism.
As well as the studies that demonstrate how dieting can in fact make you more hypothyroid, the effects of denying yourself adequate fuel in the form of food, can include fatigue, drowsiness, blood sugar imbalances, mental health risks and more, in terms of physical proof. You’re not likely to recover from your health conditions if you’re denying it adequate nutrition and fuel.
The Pressures of Losing Weight for Big Events
When I got married, I knew the pressures of dieting ‘to get slim’ for the big day.
However, I learnt to make peace with my body and instead of chronic dieting, calorie counting and weighing, I decided to instead focus on eating healthily and exercising as and when my hypothyroid body allowed (you can over-exercise), and made peace with how my body looked with it all. In short, I focused on feeling healthy inside and nourishing and looking after my body, instead of putting my already struggling body under more stress and pressure.
And I don’t regret it one bit. I didn’t lose any weight for my wedding in the end but I look back at my photos and wedding day knowing that I enjoyed it fully because I felt well. Had I carried on limiting calories, dieting and putting my body under that much stress, I would have carried on feeling mentally and physically ill and not been able to fully enjoy the occasion.
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Rachel Hill is the highly ranked and multi-award winning thyroid patient advocate, writer, speaker and author behind The Invisible Hypothyroidism. Her thyroid advocacy work includes writing articles, authoring books, producing her Thyroid Family email newsletters and speaking on podcasts, as well as being a founding board member for the American College of Thyroidology. She is well-recognised as a crucial contributor to the thyroid community and has a large social media presence. Her books include “Be Your Own Thyroid Advocate” and “You, Me and Hypothyroidism”.