Extended Low-Calorie Diets and Thyroid Dysfunction

by | Jul 5, 2021

Your body requires calories for energy to support its biological functions such as breathing, pumping blood to your heart and the rest of your body, and digestion. This is called your basal metabolic rate. If you are active and exercise regularly, your body requires even more calories. It’s important to make sure you are consuming enough calories to keep your body functioning properly. Otherwise, you may be putting your health at risk. 

The first thing people usually do when trying to lose weight is decrease their calories. This usually produces some weight loss in the beginning. Over time, however, your body’s metabolism adjusts to your reduced calorie intake, and your basal metabolic rate decreases. This means that you are no longer in a caloric deficit. When you continue to decrease your calories (and increase your physical activity), your body interprets this as a stressful event, causing it to enter starvation mode. Your body knows that you are expending more energy than it is being fed, and it holds onto everything it has. This leads to decreased efficiency of the body’s functioning, and the shutdown of many biological processes. 

Extended calorie restriction can have negative health effects

Research shows that there is a correlation between extended periods of low-calorie dieting and reduced functioning of the thyroid, as well as increased levels of cortisol. One study showed that women who restricted calories to 1200 kcal/day showed markedly increased levels of cortisol. Chronically high levels of cortisol in the body can result in a number of symptoms including weight gain, severe fatigue, and high blood pressure. That low-calorie diet you’ve been following might be increasing your cortisol levels and actually be causing weight gain. 

Another study showed that states of chronic starvation, like extended periods of extremely low-calorie diets, are associated with a decrease in total and free T4 and T3, the hormones associated with thyroid function. Decreased levels of T3 and T4 are usually present in hypothyroidism. From these studies, it is safe to assume that low-calorie diets negatively affect thyroid function, and may possibly cause hypothyroidism.

Following a low-calorie diet for extended periods of time can have negative health effects. Long-term calorie restriction can decrease your metabolism, increase cortisol levels in the body, and result in thyroid hypoactivity. After this happens, your body needs time to repair its metabolism, and it has to learn to trust that you are going to feed it before you can lose weight. This is accomplished through a practice called reverse dieting which is best done with the guidance of a registered dietitian. 

A low-calorie diet is not a long term solution

Calorie restriction is not a long-term solution for weight loss or for health. Chronic calorie restriction sends your body into starvation mode, negatively affecting your metabolism, stress levels, and thyroid activity. If you need help learning how to eat healthily or how to achieve sustainable weight loss, consult a registered dietitian for support.

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