Studies show that low-carb diets can lead to weight loss and improve metabolic health. However, while low-carb diets work well for some people, they can cause problems for others. Any diet that severely restricts calories, including some low-carb diets, can disrupt certain hormones in some women. This article explores how low-carb diets may affect women’s hormones and menstrual cycles.
The Hypothalamic-Pituitary-Adrenal (HPA) Axis and Low-Carb Diets
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. 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. 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 dysfunction.
Symptoms of HPA axis dysfunction 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. 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.
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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. Eating too few carbs or calories and experiencing chronic stress may disrupt the HPA axis, causing hormonal problems.
Low-Carb Diets, Irregular Menstrual Cycles, and Amenorrhea
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. Amenorrhea occurs as a result of the drop in levels of many hormones, such as gonadotropin-releasing hormone, which starts the menstrual cycle. 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. 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.
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 calories, especially carbohydrates, and that this can affect menstruation and other important metabolic processes. 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.
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. Following a very low carb (ketogenic) diet over a long period of time may cause irregular menstrual cycles or amenorrhea.
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The Role of Carbohydrates in 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. 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. Very low carb diets may cause a drop in thyroid function in some people. This may result in fatigue, weight gain, and low mood.
Determining Optimal Carbohydrate Intake
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. Furthermore, the Food and Drug Administration states that for a 2,000-calorie diet, the Daily Value for carbs is 275 grams per day. 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. There are other reasons to consider a moderate carb intake. Given the potential side effects of restrictive 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. A moderate carb intake may benefit some women, including those who are very active or have menstrual problems.
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When a Low-Carb Intake May Be More Suitable
Certain women may do better sticking to a low-carb diet. This includes women who have:
- 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. A lower carb intake may benefit women with obesity, epilepsy, diabetes, polycystic ovary syndrome, and some other conditions.
Ketogenic Diet and Menstrual Cycle
Patients often ask, is the keto diet safe when trying to conceive, or can keto boost my fertility? Keto has taken the storm, and certainly, there are “bad” keto diets (eggs and bacon 24/7) and wiser use of ketosis, providing a blend of healthy but high-fat choices with pious vegetable choices. High fat diet makes fat the primary fuel source and not the severely restricted carbohydrates (sugar). Balanced keto diets involve 70% of caloric intake rendered from fat, 20-25% from proteins, and the remaining from carbohydrates.
Brain fuel is glucose. However, this glucose need not come from carbohydrates. In fact, the protein component (amino acids), when broken down, provides the (re) building blocks. The liver becomes the clearinghouse and fabrication house for building the glucose to be later used by the brain and other organs. The presence of blood ketones provides the constancy of energy sources. “Ketosis” is a very different bird from “ketoacidosis.” Ketoacidosis is an unstable state and occurs when the pancreas is unable to provide adequate insulin (which shuttles glucose into the cells). It is in response to elevated ketones in the blood and is seen in people with Type I diabetes and later-stage Type II diabetes. Essentially, the pancreas remains in overdrive and cannot meet the needs of the body. The biochemistry of ketosis is what makes the ketogenic diet a powerful tool in the fight against inflammation. Inflammation drives cardiovascular disease, menstrual cycle irregularity, and obesity.
For women who have a higher BMI - body fat percentage - starting a keto diet may help restore irregular periods for some patients. It is important to determine if the patient is an appropriate candidate for the diet to experience the full benefits for your fertility. Finding the right balance is essential to maintain overall health and well-being. The optimal dietary plan is the one that is best for the patient. Increasing ketones in the blood through a keto diet or supplements may help put irregular menstrual cycles back on schedule or even restart a period that appears to have stalled for good, new research suggests.
In a study comparing weight loss results on low-fat and ketogenic diets with and without the addition of ketone supplements, 11 of 13 pre-menopausal participants who achieved nutritional ketosis reported at least one change in menstrual frequency, intensity - or both - during the intervention. Women on low-fat diets did not report any change to their periods. All women had lost the same relative percentage of weight. Their average age was 34, and all were healthy but overweight. There were six women who hadn't had a period in over a year- who felt like their typical cycles were over. And their periods actually restarted on the diet. The keto diet converts fat into ketones used by cells in the body and brain as an alternative to glucose. Supplements also elevate blood ketones without a change in eating habits. Nineteen women participated in the weight-loss diet trial - seven on a ketogenic diet alone, six on a keto diet combined with ketone salt supplements, and six on a low-fat diet. Menstrual history was one of dozens of lifestyle questions researchers asked about in biweekly assessments.
It's not a validated survey, but when researchers were reviewing responses, they realized they were changing the majority of these women's cycles. Even for women who had normal menstrual cycles, their frequency changed. One of the participants was 33 years old and had never had a period in her life. The two women who reported no change to their cycles were taking oral contraceptives. Digging deeper into findings related to ketone supplementation is one goal of research program going forward. While the addition of keto salts to the diet did not contribute to improved weight or health markers, ketone levels were high in all of the women on the keto diet - including the two whose menstruation didn't change. It was just the presence of ketones that essentially changed the menstrual cycle.
As part of evaluating and selecting a tool to standardize tracking of research participants' menstrual cycles in future studies, a team is currently monitoring a pilot group of women for the range of changes that occur between and during periods: muscle strength, fat composition, water retention, energy expenditure, hormone levels, body temperature, and more. An estimated 5 to 7% of women of reproductive age in the United States experience three months without a period each year.
Key takeaways:
- Ketosis with or without exogenous ketone supplementation resulted in realigned or restarted menses.
- After 6 weeks, ketogenic and low-fat diets both improved weight, BMI, body composition, and insulin sensitivity.
- Compared with a low-fat diet, nutritional ketosis with or without exogenous ketones may positively impact self-reported menses for women, restarting or realigning menstrual cycles, according to study results published in PLOS ONE.
- "It's not a validated survey, but when we were reviewing responses, we realized we were changing the majority of these women's cycles. Even for women who had normal menstrual cycles, their frequency changed," Madison L. Kackley, PhD, CSCS, research scientist and lecturer in the department of kinesiology at The Ohio State University, said in a related press release.
- One of the participants was 33 years old and had never had a period in her life.
Ketosis with or without exogenous ketone supplementation resulted in realigned or restarted menses. Kackley and colleagues recruited 19 premenopausal women with overweight and obesity (mean age, 34 years; mean BMI, 32.3 kg/m2) from Columbus, Ohio, to compare the impact of a hypocaloric ketogenic diet, consisting of 75% of energy to maintain weight, supplemented with and without daily exogenous ketones. Participants received a precisely weighted and formulated ketogenic diet with either twice-daily ketone salts (n = 6) or a flavor-matched placebo (n = 7) daily for 6 weeks. Researchers compared results with an age and BMI-matched cohort of six women who received a low-fat diet with a flavor-matched placebo. Both ketogenic diets provided approximately 40 g per day of carbohydrates, with remaining non-protein calories coming from fats, with an emphasis on monounsaturated and saturated fat sources. The low-fat diet contained 25% of energy from lipids, with less than 10% being saturated fat and less than 30 g of added oils. All participants self-reported menses fluctuations. Researchers also assessed body weight, body composition via dual-energy X-ray absorptiometry, and fasting blood samples biweekly. Both diets demonstrated clinically significant weight loss, primarily from fat mass and improved insulin sensitivity.
Overall, 30% of women in the ketogenic diet plus exogenous ketones group (P = .002) and 43% of women in the ketogenic diet alone group (P = .008) self-reported increased menses frequency and intensity after 14 days. After 28 days, another 30% and 33% of women in the ketosis with (P = .004) and without (P = .011) supplementation groups, respectively, reported menses restarted after a stall of more than 1 year. No women in the low-fat diet group reported changes in menses. According to the researchers, these data suggest a possible unique effect of nutritional ketosis, independent of weight loss.
The study was conducted to evaluate the impact of KD on stalled menstruation. Participants included premenopausal women aged a mean 34 years residing in the greater Columbus, Ohio area. Patients on a KD consumed approximately 40 g of carbohydrates daily, with the remaining non-protein calories obtained from fat. In comparison, those on an LFD received 25% of energy from lipids, with less than 10% being saturated fat and less than 30 g of added oils.
Women with major weight loss events, habitual consumption of a low-carbohydrate diet, gastrointestinal disorders or food allergies, excess alcohol consumption, disease conditions, or diabetic medication use were excluded from the analysis. Participants completed questionnaires about medical history, physical activity, and menstrual history.
Diet use lasted for 6 weeks, with participants attending bi-weekly in-person visits. Weight and height were measured, alongside body composition using dual x-ray absorptiometry. A trained phlebotomist used aseptic techniques to perform blood draws. Menstrual events were reported subjectively through the lifestyle changes survey. Changes were recorded on days 14, 28, and 42. Patients responding positively to questions asking if changes occurred were then asked if menstrual events differed in intensity, frequency, or if they were regained after 1 year or longer.
Baseline characteristics did not significantly differ between groups, with similar capillary beta-hydroxybutyrate (R-βHB) reported. However, participants on the KD had R-βHB boosted further than the LFD into the range of nutritional ketosis. R-βHB concentrations were not impacted by LFD. Significant changes were reported for all menses categories for both KDs assessed. This included KD with ketone salts (KS) or with flavor-matched placebo (PL). Both KD+KS and KD+PL had significant differences in the “no change” response at days 28 and 42 when compared to LFD. A significant elevation in body mass index (BMI) was reported in participants with a change in menstrual patterns vs those with no response. An increase in serum MCP-1 levels was also reported in these participants. Clinically meaningful weight loss was reported among women with a KD+PL diet at day 14, along with those on the KD+KS and the LFD by day 28. Reversing a class 1 obesity BMI to an overweight BMI was reported in 64% of patients with obesity class 1 at baseline. Patients on the LFD had a significantly reduced mean fasting insulin vs the KD+KS. Inflammatory markers were not impacted by weight loss. These results indicated clinically significant weight loss from both a KD and LFD, with a KD linked to a positive impact on self-reported menses. Investigators concluded further research may highlight novel therapeutic roles of ketosis.
Ketone Bodies and Menstrual Cycle in Epilepsy and GLUT1-DS Patients Undergoing Ketogenic Diet
Ketogenic dietary therapies (KDT) are well-established, safe, non-pharmacologic treatments used for children and adults with drug-resistant epilepsy and other neurological disorders. Ketone bodies (KBs) levels are recognized as helpful to check compliance to the KDT and to attempt titration of the diet according to the individualized needs. KBs might undergo inter-individual and intra-individual variability and can be affected by several factors. A study reported the preliminary results on six female patients affected by GLUT1DS or drug-resistant epilepsy, undergoing a stable classic ketogenic diet. A significant increase in glucose blood levels during menstruation was found in the entire cohort.
Longitudinal studies serve in identifying changes in one or more variables between different periods, describing participants’ intra-individual and inter-individual changes over time, and monitoring the degree and pattern of those changes. This is relevant for the proposed research since whether considered a reliable biomarker of KDT intervention, detecting whether KBs blood level changes are likely to occur in specific conditions, might lead to consideration of the suitability of transient preventive diet adjustments. Monitoring of urine and blood ketosis is recognized as helpful to check compliance to the KDT and to attempt titration of the diet according to the individualized needs. There is a double rationale for investigating changes in ketone bodies and glucose blood level during the menstrual cycle. Firstly, during the luteal phase, a reduction in glucose uptake related to the action of progesterone and increased insulin resistance have been documented. Secondly, interactions between seizures and menstrual cycle are possible, as suggested by variations in seizure frequency according to the day, phase, and ovulatory status of the menstrual cycle, configuring “catamenial epilepsy”.
In the small cohort analyzed, significantly higher glycemic levels were found in the overall population during menstruation period. Even though not significantly lower in the menstruation period, ketone bodies blood levels were found to be lower during menstruations in the majority of patients analyzed. These findings support the hypothesis that blood ketone bodies levels and blood glucose levels might undergo inversely proportional subtle changes during the menstrual cycle.
In conclusion, preliminary results showed a significant increase in glycemia levels during menstruation in the entire cohort and an inversely proportional trend of KB levels compared to glycemia. These data can be explained by several factors such as progesterone action and increased insulin resistance during menstruation, increase of energy requirement and thus KBs consumption during lethal phase, a reduction of KBs due to an increase of fatty acids utilization by yellow body. Importantly, not only a worsening of seizures might be a consequence of a reduction of ketone bodies blood level, but also other disease symptoms otherwise controlled by KDTs such as movement disorder, fatigue, concentration, and cognitive performance.