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Negative Side Effects of a Low-Carb Diet

author image Andrea Cespedes
Andrea Cespedes is a professionally trained chef who has focused studies in nutrition. With more than 20 years of experience in the fitness industry, she coaches cycling and running and teaches Pilates and yoga. She is an American Council on Exercise-certified personal trainer, RYT-200 and has degrees from Princeton and Columbia University.
Negative Side Effects of a Low-Carb Diet
Meals on a low-carb plan consist mostly of animal protein and watery vegetables. Photo Credit: Togapix/iStock/Getty Images

A low-carb diet makes promises that include weight loss, management of blood sugar and better fat utilization during workouts. But, reducing your intake of this major nutrient can cause unwanted side effects -- many of which linger only a few weeks as you adapt to a new way of eating. The more you decrease your carb intake, the greater the short-term side effects. You'll be less affected by a moderately low-carb diet that contains 100 to 150 grams of carbohydrates daily than by a very-low carb diet that contains 50 grams of carbs or fewer per day. If you have any particularly bothersome side effects, consult your doctor.

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Cravings on a Low-Carb Diet

If your pre-low-carb diet consisted of large servings of bread, pizza, pasta and sugary treats, a low-carb diet can leave you craving sugar and other carbs. Not only will you mentally miss these familiar foods -- many of which provide comfort -- your body will desperately seek out the quick energy fix it gets when you consume easily digested carbs.

For several days and up to three weeks, your body will adapt to a new system of energy production -- known as ketosis. When enough carbs aren't available, your body becomes more efficient at tapping into your fat stores and starts to produce ketones, which provide energy to your brain. Until this becomes your body's norm, it will do everything possible to get you to binge on carbs. If you resist the urges, within two to three weeks, the cravings should disappear.

Digestive Distress and Low-Carb Diets

A low-carb diet includes lots of meat, eggs, poultry, fish and fats. As a result, you'll be getting far less fiber than your body may be accustomed to, which may result in constipation. If you consume a lot of dairy, in the form of cheese and sour cream -- you may also feel backed up. Decrease your intake of dairy and focus on augmenting meals with plenty of watery, fibrous low-carb vegetables to keep things moving through your digestive tract.

Other people experience the opposite side effect -- diarrhea and nausea. A drastic change in diet can trigger loose stool in anyone, especially if you're limiting fat and overeating protein. Too much protein and not enough cold-pressed oils, butter, cream and nuts can lead to an unhappy digestive tract. When you drastically reduce your carb intake to 20 grams or so per day, fill out your diet with more fat and stick to only moderate amounts of protein.

The Keto Flu

A drastic switch from a standard American diet that includes 200 to 300 grams of carbs per day to one that limits you to 20 grams or fewer, can bring on symptoms affectionately known as the "keto flu." Keto refers to the state of ketosis, and as your body adapts, you may experience extreme fatigue, muscle weakness and poor exercise performance.

In addition, you may find yourself feeling forgetful and having a difficult time concentrating. Sleep may be fitful for a couple weeks, and you may suffer from headaches during the day. This can lead to irritability and a short temper as well.

To mitigate these symptoms, gradually decrease your carb intake over time. Over the course of a few weeks, reduce your carbohydrate intake by 20 grams every couple of days until you've reached your target low-carb goal.

Other Possible Side Effects

Switching to a low-carb diet often causes you to urinate more frequently than usual, and with such fluid loss you may also lose valuable minerals, such as sodium and magnesium. Muscle cramps and a "racing" heart rate can occur as a result. Ensure you get enough electrolytes when you're on a low-carb plan, and consult your doctor if these symptoms persist, as sometimes they can be a sign of other serious conditions.

In rare cases, a low-carb diet is associated with kidney stones -- usually due to a high protein intake over an extended period of time coupled with inadequate fluid intake. Some people on a very low-carb diet may also experience dysfunction in thyroid hormones. The hormone insulin is required to help you with conversion of the thyroid hormone T4, which is largely inactive, to the more active hormone T3. Insulin production tends to be quite low on a very low-carb diet, so you may experience hypothyroid symptoms such as intolerance to cold and sluggishness. Talk to your doctor about your thyroid hormone levels and follow her advice, which may include increasing your carb intake somewhat to alleviate your symptoms.

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