Written by guest writer: Mary Jane Brown, PhD, RD 

Medically Reviewed by : Dr. Michelle Dillon

Your hormones are regulated by three major glands:

  • Hypothalamus: located in your brain
  • Pituitary: located in your brain
  • Adrenals: located at the top of your kidneys

All three glands interact in complex ways to keep your hormones in balance. This is known as the hypothalamic-pituitary-adrenal (HPA) axis.

The HPA axis is responsible for regulating your stress levels, mood, emotions, digestion, immune system, sex drive, metabolism, energy levels, and more (3Trusted Source).

The glands are sensitive to things like calorie intake, stress, and exercise levels.

Long-term stress can cause you to overproduce the hormones cortisol and norepinephrine, creating an imbalance that increases pressure on the hypothalamus, pituitary, and adrenal glands (4Trusted Source).

This ongoing pressure may eventually lead to HPA axis dysfunction. Although you may have heard the term “adrenal fatigue” associated with similar health concerns from long-term stress, this is not a medical term and its use is controversial. The accepted medical term is HPA axis dysfuntion (5Trusted Source, 6Trusted Source).

Symptoms of HPA axis dysfuntion include sleep problems, a weakened immune system, and a greater risk of long-term health problems such as cardiovascular disease, stomach ulcers, and mental health conditions (7Trusted Source).

Studies of diet changes in people with obesity suggest eating too few calories can act as a stressor, increasing production of cortisol — commonly known as “the stress hormone.” However, many of these studies reported no problems with HPA axis function (2Trusted Source).

An older 2007 study found that, regardless of weight loss, a low carb diet increased cortisol levels compared to a moderate-fat, moderate-carb diet. But these researchers studied obese men only. More evidence is needed to understand the connection between diet and cortisol levels (8Trusted Source).

SUMMARY

Eating too few carbs or calories and experiencing chronic stress may disrupt the HPA axis, causing hormonal problems.

A low carb diet may cause irregular menstrual cycles or amenorrhea in some women

If your diet is very restrictive, you may experience irregular menstrual cycles or amenorrhea.

Amenorrhea is defined as the absence of a menstrual cycle for 3 months or more.

The most common cause of amenorrhea is functional hypothalamic amenorrhea, which can result from a very low calorie diet, disordered eating, losing weight, experiencing stress, or getting too much exercise. Restricting carbs could contribute to some of these causes (9Trusted Source).

Amenorrhea occurs as a result of the drop in levels of many hormones, such as gonadotropin-releasing hormone, which starts the menstrual cycle (9Trusted Source).

This results in a domino effect, causing a drop in the levels of other hormones such as luteinizing hormone, follicle-stimulating hormone, estrogen, progesterone, and testosterone (11Trusted Source).

These changes can slow some functions in the hypothalamus, the region of the brain responsible for hormone release.

A low level of leptin, a hormone produced by fat cells, is another potential cause of amenorrhea and irregular menstruation. Research suggests that women need a certain level of leptin to maintain normal menstrual function (12Trusted Source, 13Trusted Source).

If your carb or calorie consumption is too low, it may suppress your leptin levels and interfere with leptin’s ability to regulate your reproductive hormones. This is particularly true for underweight or lean women on a low carb diet.

In a 2021 narrative review of research on female athletes and their diets, the authors reported that female athletes often underconsume in calories, especially carbohydrates, and that this can affect menstruation and other important metabolic processes (14Trusted Source).

However, research on amenorrhea and low carb diets is still scarce. Studies that report amenorrhea as a side effect were usually done only in women following a predominately low carb diet for a long period of time (15Trusted Source).

One small 2003 study followed 20 teenage girls using a ketogenic (very low carb) diet to treat epilepsy. Researchers found that 45% experienced menstrual problems and 6 experienced amenorrhea during the 6-month study period (16Trusted Source).

SUMMARY

Following a very low carb (ketogenic) diet over a long period of time may cause irregular menstrual cycles or amenorrhea.

Carbs can be beneficial for thyroid function

Your thyroid gland produces two hormones: thyroxine (T4) and triiodothyronine (T3).

These two hormones are necessary for a wide range of bodily functions, including breathing, heart rate, the nervous system, body weight, temperature control, cholesterol levels, and the menstrual cycle.

In a study of people with breast cancer, the ketogenic diet in particular had no adverse effects on thyroid function. In fact, the diet had beneficial effects in that it significantly reduced levels of lactate and alkaline phosphatase (17Trusted Source).

However, other studies have found that carbohydrates can be beneficial for thyroid function and that consuming too few of them can actually lower thyroid hormone levels (18Trusted Source).

SUMMARY

Very low carb diets may cause a drop in thyroid function in some people. This may result in fatigue, weight gain, and low mood.

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