Strict "no carb" phases of low carb diets have developed a reputation for giving dieters severe headaches. Dietitians have identified a number of different factors that could cause these headaches. They vary from person to person.
One of the factors is caffeine. Most low carb diets prohibit caffeinated drinks because they cause fluctuations in blood sugar, which can potentially jeopardize the efficacy of the diet. The Atkins' diet suggests that dieters begin scaling-down caffeine consumption before they start the induction phase of the diet to minimize unpleasant withdrawals.
Another factor is wheat and sugar addictions, which can be the byproduct of reliance on refined carbohydrate products for a quick boost in blood sugar levels. If you snack to increase your blood sugar level, you may be addicted to carbohydrates, according to Dr. Atkins. Again, you may want to begin scaling-down your snacks before you start the induction phase to minimize withdrawal symptoms.
The last factor is dehydration. If you are losing weight rapidly on a "no carb" initial phase, you are also losing a lot of water that is bound-up in your carbohydrate reserves. In fact, you are actually losing four-times as many grams of water as you are grams of glycogen (or stored carbohydrates).
In addition to preventing dehydration, your body needs to replenish all of the water it loses daily to simply maintain organ functionality, flush out toxins, replace electrolytes, and promote good skin health.
Most low carb dietitians suggest that you consume 8 eight-ounce glasses of water each day. This is especially important if you are losing more than the average amount of water each day, so make sure you are sticking to the "8 x 8"--or whatever amount you can drink comfortably each day--so you don't become dehydrated during the first phase of your low carb diet.
The key to preventing low carb diet headaches is to make sure you are consuming enough water and to scale-down your potential "addictions" before you start.
If you have already started your low carb diet, there is nothing you can do about these headaches. Most experts suggest that you simply wait it out. If they don't go away after four days, then you may have food allergies, in which case you should halt the diet and consult your physician.