Studies show that low carb diets can cause weight loss and improve metabolic health (1).

However, although low carb diets are great for some people, they may cause problems for others.

Any diet that severely restricts calories, including some low carb diets, may disrupt certain hormones in some women (2).

This article explores how low carb diets may affect women’s hormones.

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Low carb and low calorie diets may affect women’s adrenals

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 (3).

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 (4).

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 (5, 6).

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 (7).

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 (2).

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 (8).

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 (9).

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

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 (11).

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 (12, 13).

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 (14).

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 (15).

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 (16).

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 (17).

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 (18).

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.

How many carbs should you eat?

The optimal amount of dietary carbs varies for each individual.

However, the Dietary Guidelines for Americans recommend that carbs make up 45–65% of your daily calorie intake (19).

Furthermore, the Food and Drug Administration states that for a 2,000-calorie diet, the Daily Value for carbs is 275 grams per day (20).

A moderate carb intake may be better for some women

A large 2018 study looked at carb intake in middle-aged adults. In this group, eating a moderate amount of carbs — that is, 50% to 55% of your total calories — was associated with the lowest risk of dying. This means that people with a moderate carb intake were likely to live longer than people with low or high carb diets (21).

There are other reasons to consider a moderate carb intake. Given the potential side effects of restictive diets, certain women may do better consuming a moderate amount of carbs.

This may include women who:

• are very active and struggle to recover after training
• have an underactive thyroid, despite taking medication
• struggle to lose weight or start gaining weight, even on a low carb diet
• have stopped menstruating or are having an irregular cycle
• have been on a very low carb diet for an extended period of time
• are pregnant or breastfeeding

For these women, benefits of a moderate-carb diet may include weight loss, improved mood and energy levels, normal menstrual function, and better sleep.

Other women, such as athletes or those trying to gain weight, may find a higher daily carb intake appropriate. Your doctor or a registered dietician can help you create a healthy eating plan.

Summary

A moderate carb intake may benefit some women, including those who are very active or have menstrual problems.

A low carb intake may be better for others

Certain women may do better sticking to a low carb diet.

This includes women who have (22, 23, 24, 25, 26):

• overweight or obesity
• a very sedentary lifestyle
• epilepsy
• polycystic ovary syndrome, fibroids, or endometriosis
• yeast overgrowth
• insulin resistance
• type 1 or type 2 diabetes
• a neurodegenerative condition such as Alzheimer’s disease or Parkinson’s disease
• certain forms of cancer

Note that “low carb” is defined differently across studies. Some diets were very low carb, in the range of 15 grams to 20 grams per day. On the higher end, some diets were less restrictive, with low carb defined as less than 45% of daily calories from carbs.

Here is more info about how many carbs you should eat.

Summary

A lower carb intake may benefit women with obesity, epilepsy, diabetes, polycystic ovary syndrome, and some other conditions.

The bottom line

Research suggests that women’s hormones are sensitive to energy availability, meaning that consuming too few calories or carbs can cause imbalances.

Such imbalances can have very serious consequences, including impaired fertility, low mood, and weight gain.

However, everyone is different, and the optimal carb intake varies greatly between individuals. There is no one-size-fits-all solution in nutrition.

Some people function best on a very low carb diet, while others function best on a moderate- to high-carb diet.

To figure out what works best for you, talk with your doctor or a registered dietitian. They can help you safely adjust your carb intake.