Detox diets have been around since the "grapefruit diet" of the 1930s. The typical modern detox diet lasts anywhere from two days to three weeks and usually involves restricted food consumption in terms of both quantity and variety. Additionally, most detox diets emphasize the elimination of caffeinated drinks and instruct you to drink more water than usual. Headaches are the most common side effect of detox diets.
Detox diets require you to cut out caffeine for the duration of the diet. If you regularly drank caffeinated beverages prior to the diet, headaches can occur from sudden caffeine withdrawal. A 1990 study published by the "British Medical Journal" discovered that headaches are one of the most likely side effects of caffeine withdrawal. Irritability and migraine attacks are also hallmarks of caffeine withdrawal.
Low Blood Sugar
Most modern detox diets involve high water consumption and severely limited calorific intake. Suddenly dropping the number of calories you consume per day can cause your blood sugar levels to decrease and this, in turn, can lead to headaches. Additionally, a sudden reduction in daily calorie intake works to slow your metabolism as your body goes into starvation mode. Low blood sugar is particularly dangerous if you have diabetes or epilepsy.
One serious possible cause of headaches during a detox diet is hyponatraemia, also known as water intoxication. Hyponatraemia was identified as the cause of serious neurological side effects for Dawn Page, a British woman who suffered permanent brain damage in 2008 as a result of drinking too much water as advised by a detox diet, according to the BBC. Drinking too much water can dilute the blood, flooding cells and organs with water as sodium levels decrease. This, in turn, can cause swelling of cells in your brain and an increase in pressure in the skull. Headaches can result from this increase in skull pressure. Other more serious possible side effects of hyponatraemia include seizures and breathing problems.