Low-Carb Diets and Muscle Aches in the Legs

There are many potential benefits to reducing your carb intake, including weight loss and improved heart health. But the shift to a low-carb diet can be a rocky road, strewn with obstacles that make you want to pop out for a pizza. Muscle cramps are just one of the many potential side effects you may experience when starting your diet, although probably not as common as some of the others.

A low carb diet can cause muscle aches in the legs. Credit: Michael Heim / EyeEm/EyeEm/GettyImages

Types of Low-Carb Diets

Reducing your carbs below the recommended daily minimum amount of 130 grams technically results in a "low-carb diet." But most people reduce their carb intake by much more than that. For example, the Atkins 20 diet limits carb intake to about 20 grams a day.

This type of very low-carb diet is called a ketogenic diet, and it involves getting most of your daily calories from fats and a smaller amount from protein. But, you may also be following a low-carb, high-protein diet that increases your protein intake instead of your fat intake. There are benefits to both types of diets.

Some people may just want to clean up their diet, cutting out the unhealthy carbs from sugar and refined grains. Giving up sodas, cakes, cookies, candy, chips, white bread and other junk foods can significantly lower the number of carbs you eat and have dramatic benefits for your health.

Low-Carb Diet Side Effects

The side effects you may experience when starting a low-carb diet depend on the extent to which you cut carbs. They also depend on your own sensitivity to a lack of carbs. If you previously ate a high-carbohydrate diet, and you switch to a ketogenic diet, you are likely to feel more marked side effects than someone who makes a more moderate change.

Side effects of a very low-carb diet like the keto diet may include:

  • Fatigue
  • Headache
  • Nausea
  • Vomiting
  • Dizziness
  • Insomnia
  • Reduced exercise intolerance
  • Constipation or diarrhea
  • Skin rash
  • Bad breath
  • Weakness
  • Muscle cramps

These symptoms are often referred to as the "keto flu." They aren't a virus like the flu, but they can cause you to feel tired and achy as if you have the dreaded bug. Much like the flu, these symptoms are at their worst in the first few days, then gradually begin to improve.

Read more: 16 Diet-Friendly Healthful Carbs

Sore Muscles on Keto

No one is quite sure of the causes of keto leg pain. In general, most people feel run down and icky during the first few days of the keto diet because their bodies are trying to adapt to the huge dietary change.

Your body likes to maintain homeostasis, or a state of balance. Suddenly taking away carbs, its preferred source of energy, can throw your body into a tailspin. Now, the body has to search for another means of providing energy, burning fat and creating ketones, in a metabolic process known as ketosis.

The effects of ketones on the body aren't well understood. In people with diabetes, a buildup of ketones in the blood causes a dangerous condition called ketoacidosis, which can have side effects including fatigue, nausea, weakness, shortness of breath and a fruity odor to the breath. This is not the same as ketosis, which is a natural process that raises ketone levels but not nearly as high as in ketoacidosis; however, ketones may be responsible for some of the uncomfortable side effects you experience.

In addition, when you drastically reduce your carbs, you lose a lot of water weight in the first few days. In fact, most of the weight loss you'll see at the beginning of a diet is water loss. If you're not adequately replacing these fluids, you risk dehydration, primary symptoms of which include muscle cramps.

If you're also exercising during this time, you risk even more fluid loss through sweat. Doing vigorous activities such as running or interval training while dehydrated can make matters worse. Putting stress on muscles that are already fatigued from lack of carbs and fluids will likely result in greater muscle damage and soreness after your workout.

Lastly, fluid loss and cutting carbs can lead to losses of important electrolyte minerals, including magnesium, potassium, calcium and sodium. Collectively, these minerals play a major role in muscle function, and being deficient in one or more of them can cause keto leg pain.

Read more: 9 Tasty Tips for Cutting Carbs From Your Diet

Help for Keto Leg Pain

Like many of the symptoms of ketosis, leg cramps are typically short-lived. As your body adapts to the change, your legs should start to feel better. In the meantime, here are a few tips to minimize your discomfort:

Take it easy: Don't put any more stress on your legs than you need to. There's no need to stop exercising — in fact, light exercise may even help — but this is probably not a good week to increase your marathon training mileage, run sprints or hike Mt. Kilimanjaro. Instead, opt for short sessions of low- to moderate-intensity activities like brisk walking.

Drink up: It's crucial to focus on proper hydration during this time. According to the Mayo Clinic, men need 15.5 cups of fluids per day and women need about 11.5 cups daily. While about 20 percent of this comes from the foods you eat, most comes from drinking water and other unsweetened beverages.

Keep track of your fluid intake to make sure you're reaching your goal. You can also weigh yourself — especially before and after exercise — and try to replace the weight you have lost with extra fluids. As mentioned earlier, this is not fat loss — it's water loss. If your weight is dropping, you're probably becoming dehydrated.

Replace electrolyte minerals: Most people can get all the electrolyte minerals they need through their diet. Eat plenty of leafy greens, snack on some keto-friendly nuts like pecans, and add a little extra salt to your meals.

If your keto leg cramps don't subside after a week, you should check in with your doctor. Leg pain and leg cramps have myriad causes that may not be due to your diet change. Tell your doctor about any other changes you've made recently, or any other changes in your health that you've noticed so you can get an accurate diagnosis.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.
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