Intermittent fasting [1] can do a world of good — those who practice it often lose weight [2] and feel more energized and less bloated [3], among other benefits. But it's not without side effects [4], including pesky headaches. Fortunately, there are ways to prevent them once you've figured out the cause.
One of the most common causes of fasting-induced headaches is low blood sugar, triggered by eating fewer calories. "Fluctuations in blood sugar are a common cause of headaches, as are shifts in stress adaptive hormones such as cortisol," Lisa Powell, MS, a registered dietitian at Canyon Ranch [5] in Tucson, AZ, told POPSUGAR. "These issues should resolve as the body adjusts to the lower calorie intake."
To help it along, you can also make changes to your menu. "Try taking in more calories from fat [6] during the periods that you are not fasting," suggested Iris Lami, an ACE-certified personal trainer in Kealakekua, HI. "Doing so helps your body become less reliant on sugar for fuel, making you less likely to experience severe blood sugar drops when you do begin fasting."
Then there's the issue of dehydration, which can not only cause headaches during intermittent fasting, but also slow digestion, leading to more bloat [7]. "It's important to maintain adequate hydration, especially when fasting," Lisa said. "I recommend drinking half of your current body weight in fluid ounces per day as a baseline. So, for example, a 150-pound person would need about 75 ounces of fluid per day, not including alcohol, which is significantly dehydrating. Some individuals may even need more fluids than this, depending on climate, exercise, and personal needs."
