What is happening in your body during the introduction diet? Several things:
- Herxheimer Reaction. During the introduction diet, most people who are doing the diet to heal significant health problems will be experiencing a Herxheimer reaction, which is a temporary worsening of symptoms due to die-off of harmful flora. Symptoms may include fever, nausea, diarrhea, constipation, flu-like symptoms, headache, etc. For myself, who was a chronic-fatigue profile with yeast overgrowth, I experienced about 10 days of mild "intoxication" symptoms. As crazy as that sounds, it is actually possible for the brain to become "drunk" from all the toxins being released from flora die-off (See Gut and Psychology Syndrome by Dr. NCM, pages 50-53; see also multiple scientific studies/articles on "auto-brewery syndrome" here; and an interesting case report here.). I felt slightly dizzy, befuddled in my thinking, and slightly blurry of vision. Also, my fatigue increased significantly and I had insomnia - my brain just would not turn off to go to sleep. In short, I was pretty incapacitated. Obviously I was an extreme case, but if you are really sick, then chances are it won't be pleasant for the first couple weeks.
- Sugar Withdrawal. In addition to "herxing," most people will also be having carbohydrate withdrawal symptoms. Yes, sugar is actually biologically addictive to your body, and you will probably get the shakes and grumpies from withdrawal (see this scientific study which found that refined sugar is more addictive than cocaine!). Even if you thought you weren't eating that much sugar before, you would be surprised how much sugar you were feeding your body from grains, starchy vegetables, processed foods, and that daily dessert or soft drink.
- Metabolic Shifting. Also, the body will be learning how to switch from a carbohydrate-driven metabolism to a fat-driven metabolism. Your body has been primarily processing its energy from carbohydrates, and now it has to learn how obtain its energy primarily from healthy fats. This is a huge shift in how your body functions, and it will likely include some low blood sugar symptoms temporarily until things balance out (see this helpful article about fat adaptation).
- Physiological Fasting. The first few stages of the GAPS introduction diet are also essentially a form of fasting. During a fast, your body is focusing less on digestion and more on detoxification and rebuilding, and numerous physiological changes occur. For example, during a fast your body cleans out old, worn out white blood cells and replaces them with fresh new ones, thereby giving your immune system a little "reset" (see a study about this here). Intermittent fasting also has an anti-inflammatory effect (see a study here). Of course, your body is working hard to do all this, and you may feel increased fatigue at first (see a helpful article about intermittent fasting here; and a scientific article about fasting benefits here).
Two years after my own journey on the introduction diet, I am now able to do strenuous physical exercise, like heavy yardwork, for hours on end without feeling weak or hungry. Whereas two years ago, exercise would have only been perceived by my body as an added stressor that contributed to further physical breakdown, now my body is now able to respond to physical exertion with beneficial rebuilding and strengthening.