What is Carb Flu? and how to avoid it

carb flu

So you’re about four days into starting the Autoimmune Protocol and you feel like total crap, experiencing everything from headaches and fatigue to achy muscles and brain fog. At this point you’re probably thinking, “What is happening? I thought this protocol was supposed to help me feel better, not worse?!” Don’t worry, you don’t have the flu… at least not the viral kind! You’ve got carb flu.

When you switch from a conventional diet that is low in healthy fats and high in grains and processed sugar to one that is, well, the exact opposite, there is a good chance you’ll experience those lovely flu-like symptoms. This uncomfortable transition period is often called “carb flu” and is caused by your body changing how it gets energy.

What is “Carb Flu”?

The body has two primary fuel sources, healthy fats and carbohydrates, and these are broken down into glucose, or blood sugar, which give the body energy to function. The process of breaking down carbohydrates into glucose is a much faster and simpler process than breaking down fats, so carbs tends to be the first resort for the body when it needs energy fast. Refined carbohydrates (grains and processed sugar) are broken down even faster than whole-food based carb sources (vegetables).

If you’ve been eating a diet high in refined carbohydrates, your body is used to rapidly breaking those down to get a “energy hit” and relies heavily on this fuel source. When you remove these refined carbs and replace them with whole-food carbohydrates, protein, and healthy fat, the body must now create more fuel from fats and protein, instead of carbs. This process is completely natural but slightly more complex, so it can take time to get up to speed.

We feel this fuel-source-transition as increased fatigue, muscle aches, headaches, and brain fog while our body is trying to adjust how it creates energy. Don’t worry, there are some ways you can either avoid this process completely or at least help speed it up.

How to Avoid It

What is carb flu

Know Your Starchy Carb Sources. The Autoimmune Protocol is not inherently a low-carb diet. There are plenty of starchy carbohydrate sources available, you just have to be creative in your menu planning. If you’re coming to AIP from a diet high in refined carbs, be sure to include plenty starchy vegetables, especially in the beginning. Here are a few examples:

  • Sweet Potatoes (orange, white, and purple)
  • Plantains
  • Cassava or Yuca
  • Rutabaga
  • Taro
  • Parsnips
  • Winter Squash
  • Yam

Include Plenty of Healthy Fats. Fat is one of the body’s primary fuel sources, so be sure to include plenty of healthy fats with every meal. This makes sure your body has enough fuel to burn while its transitioning away from refined carbohydrates. You can use generous amounts while cooking or drizzle over your veggies before eating. Here are a few examples:

  • Coconut Oil
  • Animal Fats (lard, tallow, duck fat)
  • Avocado Oil
  • Olive Oil (only for low-heat cooking or finishing)
  • Avocados
  • Fatty fish (salmon, anchovies, tuna)

Drink Enough Water. The symptoms of carb flu can be made worse by dehydration, so make sure you’re drinking plenty of hydrating liquids and avoiding diuretics like coffee, caffeine, and certain herbal teas (ginger, peppermint, dandelion.) Adding a pinch of sea salt or mineral salt to your water can help increase absorption, so your body doesn’t pee it all out. To calculate how much water you should be drinking, follow this equation:

(half your body weight in ounces / 2) + (amount of diuretics consumed in ounces x 1.5) = goal water intake

Here is an example equation for someone who weighs 150lbs and drinks one 12oz cup of coffee:

(150/2) + (12 x 1.5) = 93oz of water


Jesse St. Jean

Jesse St. Jean

I am many things: a wife, a daughter, a sister, a nutritional therapist, a dog-mom… and I’m an autoimmune warrior.

Nutritional therapist Jesse

Hi, I'm Jesse

I empower women autoimmune warriors to reclaim their health by teaching each woman how to make the right food choices to heal her body while confidently owning her journey so she can live a vibrant life with chronic illness.


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