This article was written by Registered Nutritionist Sophie Gastman and Registered Dietitian Maeve Hanan.

Low-carbohydrate diets have been around for a long time, but they became particularly popular in the 1960s when the Atkins diet arrived on the scene. Despite its popularity as a weight-loss method, most people fail to recognise the cost that maintaining a low-carbohydrate diet can have on our health, especially our hormones. 

Carbohydrates and Reproductive Hormones

Female hormones in particular are extremely sensitive to our diet. This means that not providing your body with an adequate amount of calories or carbohydrates can cause significant disruptions to the production of the key female hormones, such as luteinizing hormone (LH), follicle-stimulating hormone (FSH), oestrogen, progesterone and testosterone (1). These hormones are vital for efficient reproductive processes.

A number of these female hormones are made in the hypothalamus and pituitary glands in the brain. These glands work in combination with the adrenal gland to form the hypothalamic-pituitary-adrenal (HPA) axis, which regulates functions like: mood, digestion, stress response, immunity, libido, metabolism and energy levels. All components of the HPA axis are very sensitive to factors like stress and not having enough energy available in the body. Thus, failing to consume either enough calories or carbohydrates can have a knock-on effect, negatively impacting female fertility, which may lead to issues such as hypothalamic amenorrhea (absence of a natural period) or irregular periods. For example, one study following 45 patients aged 12-19 on a ketogenic diet found menstrual dysfunction was the most common side effect (45% of female subjects) and 6 experienced amenorrhea (2).

On top of this, hormone imbalances caused by lack of energy, which can occur on a low-carbohydrate diet, can also lead to loss of bone density, increased inflammation, worsened heart health, lack of energy, disrupted sleep, low moods and an increased chance of fat storage (particularly around the abdomen).

To add fuel to the fire, not eating enough carbohydrates has been linked with higher cortisol levels (stress hormone) (3), which can further reduce the function of the pituitary gland and make the problem worse. One controlled feeding intervention study in young adults in the higher weight categories found that those on a very low-carbohydrate diet had the highest levels of cortisol, despite showing the greatest improvements in components of the metabolic syndrome (4). 

Carbohydrate and Hunger Hormones

Low carbohydrate or calorie consumption has also been shown to suppress your levels of leptin (5). Leptin is a hormone released by the fat cells and helps the body maintain its weight by inhibiting hunger and regulating energy balance. For this reason, it is sometimes referred to as the ‘satiety’ or ‘fullness hormone’. Aside from the obvious consequences of low leptin levels, such as increased hunger, it can also lead to amenorrhea. In fact, evidence suggests that a specific level of leptin is required to maintain menstruation (6).

Carbohydrate and Thyroid Hormones

Finally, low-carbohydrate diets can affect the function of your thyroid hormones, which are important for a whole range of bodily functions from heart rate, to cholesterol, to your menstrual cycle. The thyroid gland produces two hormones: thyroxine (T4) and triiodothyronine (T3), and as with the other hormones mentioned in this article, these are also very sensitive to carbohydrate and calorie consumption. Low intakes of carbohydrates can reduce the levels of T3 in the body. One study found that serum T3 levels decreased rapidly in women following a low carbohydrate very-low-caloric diet (7), however this fall in T3 can easily be reversed simply by consuming more carbohydrates (8). Negative consequences of low T3 levels can include lack of concentration, low mood and weight gain. 

Who May Benefit From Increasing Their Carbohydrate Intake?

Every situation is different, so it is important to seek individual advice from a qualified health professional if you are concerned about your diet or carbohydrate intake.

Some examples of cases where increasing carbohydrate may be beneficial include:

• Women who are physically active and have a hard time recovering after training 
• Women who are suffering from hypothalamic amenorrhea
• Women who are pregnant or breastfeeding 
• Those recovering from an eating disorder
• Those who restrict their carbohydrate intake but who want to achieve more freedom and flexibility with food

Take Home Message

Overall, everyone’s carbohydrate needs are different, but it’s important to be mindful of the sensitivity and consequential imbalance of female hormones when considering your diet. Moderation is key and most of us will perform and function our best when we maintain a balanced diet without heavily restricting any single macronutrient. Check out this article for more information about the importance of carbohydrates. 

References

1. Loucks, A., Verdun, M. and Heath, E., 1998. Low energy availability, not stress of exercise, alters LH pulsatility in exercising women. Journal of Applied Physiology, 84(1), pp.37-46.
2. Mady, M., Kossoff, E., McGregor, A., Wheless, J., Pyzik, P. and Freeman, J., 2003. The Ketogenic Diet: Adolescents Can Do It, Too. Epilepsia, 44(6), pp.847-851.
3. Stachowicz, M. and Lebiedzińska, A., 2016. The effect of diet components on the level of cortisol. European Food Research and Technology, 242(12), pp.2001-2009.
4. Ebbeling, C., Swain, J., Feldman, H., Wong, W., Hachey, D., Garcia-Lago, E. and Ludwig, D., 2012. Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance. JAMA, 307(24).
5. Jenkins, A., Markovic, T., Fleury, A. and Campbell, L., 1997. Carbohydrate intake and short-term regulation of leptin in humans. Diabetologia, 40(3), pp.348-351.
6. Köpp, W., Blum, W., von Prittwitz, S., Ziegler, A., Lübbert, H., Emons, G., Herzog, W., Herpertz, S., Deter, H., Remschmidt, H. and Hebebrand, J., 1997. Low leptin levels predict amenorrhea in underweight and eating disordered females. Molecular Psychiatry, 2(4), pp.335-340.
7. Mathieson, R., Walberg, J., Gwazdauskas, F., Hinkle, D. and Gregg, J., 1986. The effect of varying carbohydrate content of a very-low-caloric diet on resting metabolic rate and thyroid hormones. Metabolism, 35(5), pp.394-398.
8. Azizi, F., 1978. Effect of dietary composition on fasting-induced changes in serum thyroid hormones and thyrotropin. Metabolism, 27(8), pp.935-942.