Low-Carb Diets May Harm Sleep and Cognitive Function, Doctor Warns

Restricting carbohydrates too severely may negatively impact your health, potentially causing issues like insomnia and brain fog, warns physician Li Sixian. She explains that long-term, very low carbohydrate intake can disrupt the regulation of the body's stress hormone, cortisol, affecting sleep and mental well-being.

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For some people, keeping carbohydrates very low long-term may be quietly raising their cortisol.

Li cites a 2019 study published in Nutrients, which found that women who increased their carbohydrate intake showed significantly lower cortisol levels after stress tests compared to a control group. This suggests that consuming more whole-food carbohydrates can buffer the body's cortisol response to stress.

The mechanism involves insulin, which rises with carbohydrate intake. Insulin helps transport amino acids, reducing competition for tryptophan. Tryptophan is a precursor to serotonin, a neurotransmitter that can cross the blood-brain barrier more easily. Increased serotonin in the brain can lower the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis, the system controlling cortisol secretion.

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The feeling of elevated cortisol is stress, anxiety, poor sleep quality, brain fog, and an indescribable 'tightness'.

Crucially, the study focused on whole-food carbohydrates such as vegetables, beans, and whole grains, not refined sugars or processed foods. Li advises that if you are on a low-carb diet and experience increased chronic stress, poorer sleep, or heightened anxiety, it might be a sign your body's cortisol levels are suffering. This is particularly relevant for those with high-stress lifestyles, chronic sleep issues, or women, who may be more sensitive to dietary changes.

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This means that people who ate more whole-food carbohydrates had a significantly blunted cortisol response to the same stress.

Li recommends considering a moderate increase in whole-food carbohydrates like sweet potatoes, beans, brown rice, and vegetables to see if symptoms improve. She emphasizes that sleep, mood, and stress management are as important for assessing health as weight and blood sugar.

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If you are on a low-carb diet and simultaneously experience increased chronic stress, decreased sleep quality, increased anxiety, and greater mood swings, it indicates that your body's cortisol levels are paying the price.