Low Carb Diet Side Effects

Low carb diet side effects are completely manageable if you understand why they happen and how to minimize them. This is why you want to get one of the books I recommend on low carb diets and read it. Understanding your physical reactions will help you avoid the worst of the symptoms, and keep you from quitting before you get out of the chute, so to speak.

After several weeks, these side effects will subside as you become "keto-adapted" and able to burn fat instead of glucose for fuel. The list below includes the most common low carb diet side effects, and I've included tips on how to handle them.

Frequent Urination

After the first day or so, you'll notice that you are in the bathroom urinating more often. Your body is burning up the extra glycogen (stored glucose) in your liver and muscles. Breaking down glycogen releases a lot of water. As your carb intake and glycogen stores drop, your kidneys will start dumping the excess water.

In addition, as your circulating insulin levels drop, your kidneys start excreting excess sodium, which will also cause more frequent urination. (see this reference).

Fatigue and Dizziness

As you start dumping water, you'll lose minerals such as salt, potassium and magnesium as well. Having lower levels of these minerals will make you very, very tired, lightheaded or dizzy, give you muscle cramps, and headaches. This is one of the most common of the low carb diet side effects, and it can be avoided for the most part by making sure you get enough replacement minerals.

You can counteract the mineral losses by eating more salt or drinking salty broth, and eating potassium containing foods. (Dairy foods, green leafy vegetables and avocados are high in potassium).

As long as your carb intake is below 60 carbs a day, you will need to continue to eat a moderate amount of salt (5 gram/day which is about the same as the standard American diet provides). However, if you take medicine for high blood pressure, check with your doctor.

In addition, you may want to take 400 mg of magnesium citrate every night before bed. (Check with your doctor first if you have kidney or heart health issues).

It's also really important to eat at least 2 cups of raw green leafy vegetables every day. These vegetables provide potassium and vitamin K, and will also help with hunger.

Reactive Hypoglycemia

If you've been eating a higher carb diet, your body is used to putting out a certain amount of insulin to take care of the sugar which gets created from all that carbohydrate intake.

When you suddenly drop your carb intake on a ketogenic diet plan, you may have some transient low blood sugar episodes that will feel very scary. See my reactive hypoglycemia page for more information on the symptoms, and what to do.


This is another one of the most common low carb diet side effects, and is usually a function of dehydration, salt loss and possibly magnesium imbalances. The magnesium mentioned under the fatigue entry above will help with this. If 400 mg of magnesium citrate isn't helping, you may want to cut back on your dairy product consumption to rebalance your calcium intake to your magnesium intake, drink lots more water and try sautéed greens such as kale or cabbage. You could also add a teaspoon of psyllium husk powder to your diet. This will help draw water to your colon. However, if you are severely constipated, don't use psyllium husk until you have resolved any blockage first. Treatments such as polyethylene glycol (peg) 3350 (Miralax or Movicol) can be used, and may need to be prescribed by your doctor.

You could also add another 100 mg of magnesium to your daily intake, but don't take more than that. Magnesium is powerful stuff, too much can cause heartbeat irregularities and other serious health issues, so you don't want to take too much. You'll know if you have because you'll spend significant time in the bathroom.

Sugar Cravings

As your body goes through the process of retrofitting itself to burn fat instead of sugar, there's a 2-10 day transition period where carb cravings will be worse. Try some of tips I recommend on how to stop sugar cravings. If you can wait it out, the cravings will subside and eventually disappear, as long as you don't cheat. Eating a large amount of carb will bring the cravings right back.


Being in ketosis can cause headaches for some people. You may also feel a little lightheaded, and may experience some flu-like symptoms for a few days. Up your salt and water intake, and power through it, if you can. It will get better after 3-4 days. If it doesn't, add a little more carb to your daily total. This is one of those low carb diet side effects for which I don't have a solid explanation, and it seems to vary by person.


This usually happens to people who unwisely decide to also limit their fat intake on a low carb diet, which results in eating too much protein. Eating a high protein, low carb AND low fat diet will cause symptoms of "rabbit starvation". My advice is to not fall into that trap. Make sure you replace the carbs you are cutting with more fat, preferably saturated fat such as butter or coconut oil. Following a ketogenic diet menu means you can choose fattier cuts of meat, and use heavy cream in your coffee.

Shakiness or weakness

This is a side effect of hypoglycemia or low blood sugar. It could also be a symptom of low mineral levels. Add some more protein to your daily diet to offset the drop in blood sugar levels, and eat more salt (put a 1/4 teaspoon of salt in a glass of water and drink it) and include more potassium containing foods. You could also take a 99 mg potassium citrate supplement.

Muscle Cramps

This is another side effect of the loss of minerals, specifically magnesium. In their excellent book The Art and Science of Low Carbohydrate Living: An Expert Guide to Making the Life-Saving Benefits of Carbohydrate Restriction Sustainable and Enjoyable, Drs. Jeff Volek and Stephen Phinney recommend taking 3 slow release magnesium tablets such as Slow-Mag or Mag 64 for 20 days, then continuing to take 1 tablet a day afterwards. NOTE: if you have kidney problems or kidney failure, don't take oral magnesium supplements without checking with your doctor.

Sleep Disturbances

Some people report that they can't stay asleep when on a ketogenic diet. This may be an indication that insulin and serotonin are low. Try this solution: eat a snack which contains both protein and some carbohydrate right before bed. The carbohydrate will increase insulin, which will allow more tryptophan from the protein to get into the brain. Tryptoplan is the precursor for serotonin which has a calming effect on the brain. See this article and this paper. Greek yogurt with a 1/2 tablespoon of fruit spread or a little square of 70% chocolate is one possibility. This is another of those low carb diet side effects which seems to vary by person. I wish somebody would do a study on this.

In addition, there may be a histamine intolerance involved. Low carb diets are higher in histamine containing foods, and some people react to higher intake of these foods with anxiety and sleeplessness. See this post on histamine intolerance.

Kidney Stones

Dietitans will bring this side effect up when they are trying to convince people that ketogenic diets are dangerous. They base this on the reports of higher rates of calcium based kidney stones reported by physicians who administer ketogenic diets for children with epilepsy. The latest research on stone formation on ketogenic diets suggests that stones form more easily in the presence of not enough water, too much sodium and not enough potassium in the diet. See this paper. Low carb foods which are high in potassium include avocado, no or low fat yogurt, chicken, meats, fish and dark leafy greens.

So, there you are. These low carb diet side effects are just minor issues, and over a period of several weeks, they will get better and finally subside. After that, you ought to be feeling pretty darned good!

Done with Low Carb Diet Side Effects, back to Ketogenic Diet Plan

My Favorite Low Carb Cookbooks