Dizziness can occur in the first few days, or even week, of a low-carb diet as you adapt to this new way of eating. Loss of water, and consequently electrolytes, as well as plummeting blood sugar levels may make you feel fatigued and lightheaded. Don't skimp too much on calories and stay ahead of mineral loss to head off this unpleasant side effect.
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Dizziness: A Symptom of the Keto Flu
When you lower your carb intake to 50 grams or fewer per day, most people shift into a state of ketosis. Ketosis occurs when your body ups fat burning and produces ketones for energy, rather than using glycogen from carbohydrates. While this is a natural state, if you previously consumed the 200 to 300 grams of carbs -- or more -- in a standard American diet, it takes time to adjust.
The "keto flu" describes some of the unpleasant symptoms that occur during this adjustment period. You feel almost as if you've been stricken by a true illness -- poor energy, lack of focus, sleep disturbances, exercise intolerance, digestive distress and dizziness are common symptoms. The keto flu usually lasts just a couple of days, or up to a week, as your body adapts to using fat and ketones for energy.
Low Blood Sugar on a Low-Carb Diet
One of the side effects of a low-carb diet is lower blood sugar. If prior to following a low-carb diet you ate a lot of carbohydrates, your body is accustomed to pumping out lots of insulin to help you process the resulting high blood sugar levels. When you first switch to a low-carb plan, you're not eating the same number of carbs, but your body may still pump out high levels of insulin -- leaving you with extremely low blood sugar levels. Symptoms of this reactive hypoglycemia include dizziness, headaches, heart palpitations, extreme hunger and nausea.
To avoid this temporary hypoglycemia, consider easing into a low-carb diet rather than cutting back drastically all at once. Eating more frequently also helps -- aim for a meal or snack every three to four hours.
A Low-Carb Diet and Mineral Imbalance
As you adapt to a low-carb plan and your body stops pumping out large amounts of insulin, your kidneys get a message to let go of salt and the accompanying water. You'll urinate more frequently, losing not just water, but precious minerals called electrolytes that support muscle and heart function. An electrolyte imbalance and the possible resulting low blood pressure can cause muscle cramps and lightheadedness.
These minerals include potassium, sodium and magnesium, which can easily be replaced with a drink that includes electrolytes -- such as those used by athletes during endurance events. Look for ones without added sugar, or you'll get unwanted carbs. Talk to your doctor about potentially taking an oral supplement to help, too.
Adequate Calories and Hydration
If you cut back on carbs and fat at the same time, you may end up eating too few calories and make it hard for your body to start burning fat for fuel and producing ketones. Eat until you're full, especially when starting the diet. Include fatty cuts of meat, olive and coconut oil and scant servings of nuts. You'll still likely lose weight as you shift into ketosis.
As your body loses water weight during the first few days of a low-carb plan, you're also vulnerable to dehydration. In addition to other signs, like dark-colored urine and fatigue, feeling dizzy when you move quickly from sitting to standing can be a sign. Increase your water intake and drink until your urine resembles light lemonade.