Most likely, your headache isn't caused by a withdrawal from carbohydrates, but rather a withdrawal from a specific type of carbohydrate -- sugar. When you eat a high-sugar diet, your body quickly becomes adjusted to a ready supply of glucose, your body's preferred source of energy. When your body doesn't have the sugar it needs, you may experience low blood sugar, or hypoglycemia. Symptoms of hypoglycemia include hunger, headache and fatigue.
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Your body uses glucose for energy. When you eat, particularly quickly digested carbohydrates such as sugar and starch, that food is converted to glucose and released into your bloodstream. Your pancreas then produces insulin to help transport glucose from your blood into your cells. Glucose can be used right away for energy, or stored in your muscle tissue and fat cells for later use. When you don't have a ready supply of glucose, you may experience a headache -- as your body can use stored energy from muscle or fat better than your brain, which really prefers glucose.
Regulating Blood Sugar
To avoid sugar-related headaches, try to keep your glucose levels stable. Some fluctuations are normal, especially before and after eating, but if you stop the fast flood of glucose that comes from eating a too many simple carbohydrates, you will prevent the inevitable blood sugar crash and headache that follows. You can keep glucose levels stable by eating smaller frequent meals, every three to four hours. Both the quantity and quality of your food matter; if you wait too long between meals, you may be so hungry that you eat very quickly and end up consuming too much food.
Dietary Changes and the Glycemic Index
You don't need to follow a low-carb diet to avoid hypoglycemia, but you do need to make better carb choices. Eating high-fiber complex carbohydrates, which includes fruits, vegetables, legumes and whole grains, will slow digestion and the conversion of food into glucose. The glycemic index is a toll that ranks foods by their potential impact on your blood sugar -- the lower a food scores on the GI, the less effect it has on blood sugar. The majority of your carb choices should score 55 or less on the GI.
Diet and Headaches
When you have low blood sugar, you body starts to use stored energy while waiting for a fresh supply of glucose. Special hormones are released that help your body convert this stored energy back into a usable form. These hormones contribute to your headache because they can narrow blood vessels and raise blood pressure. Again, keeping blood sugar levels stable will help prevent your body from releasing these hormones and prevent your sugar-related headache.