After working as a neurologist and a neurosurgeon for eight years, Campbell-McBride launched the Cambridge Nutrition Clinic in 1998, where she specialized in nutritional approaches to treating learning disabilities, psychological disorders and digestive and immune disorders in children and adults.

As she collected patient data, she noticed two consistent threads: first, most patients had some kind of active digestive issues, and, second, the occurrence of seemingly unrelated conditions overlapped. Children who were admitted for autism, for example, commonly suffered from other conditions such as hyperactivity, severe allergies, asthma and dyslexia. And it was discovered that many who had suffered severe eczema in infancy frequently developed autistic symptoms later in life. “I have yet to meet a child with autism, ADHD/ADD, asthma, eczema, or dyslexia who has not got digestive abnormalities,” says Campbell-McBride.

Since publication, Campbell-McBride has heard from people around the world who have adopted the GAPS diet and have gotten unexpectedly positive and definitive results with it. “When they start the GAPS nutritional protocol, we find that people recover from rheumatoid arthritis, chronic fatigue syndrome, multiple sclerosis, type 1 diabetes, chronic cystitis, asthma—from all sorts of problems—showing us that the disease was rooted in the gut.”

The book has since been translated into 23 languages.  

While most of us might not be aware of it, the digestive system does a great deal more than simply digest food. It plays a large, essential and pivotal role in keeping the body healthy and preventing illness and disease.

“The digestive system is a highly sophisticated and highly complex microbial community; it’s just as complex as life on earth itself,” says Campbell-McBride. She points out that 90% of all cells in the human body are located in the gut, and up to 85% of the cells that participate in the immune system are housed in the walls of the digestive system. When the gut’s complex ecosystem is balanced, the body stays healthy, and the immune system stays strong. And when it is weakened and its delicate balance is disturbed, the body becomes vulnerable to symptoms, illness and disease.

Unfortunately, compromised and polluted environments, food supplies, food choices and even adverse human genetics can play havoc with the gut’s microbial balance. “Every time we take antibiotics, for example,” says Campbell-McBride, “bacteria are killed off, bacteria that had been eating and controlling a myriad of other creatures to help keep the balance. Suddenly all those creatures become uncontrolled. They overgrow. Then, organisms that used to be perfectly beneficial within a whole, balanced community suddenly become pathogenic.”

But the problem goes well beyond what we put in our mouths. The health of gut flora can pass through the generations, according to Campbell-McBride. “We now have generations of people that have been exposed to a damaging environment, and they pass the damaged gut flora to their children, generation after generation.” In addition, the foods we eat are more denatured, and more damaging drugs are introduced in the market. The contraceptive pill, for example, has a devastating effect on a woman’s gut and immune system, says Campbell-McBride.

What happens when gut flora gets out of balance? The gut wall itself—normally a fortress of protection of the immune system—deteriorates very quickly. “When the microbial community in the gut is damaged, its walls are less able to stay sealed, gaps develop, and it becomes porous and leaky,” says Campbell-McBride. The condition, sometimes called “leaky gut,” means the gut lining is damaged by abnormal microflora, and foods don’t get properly digested before they’re absorbed into the bloodstream.

Next, the immune system, which normally polices the contents of the blood looking for troublesome invaders, doesn’t recognize undigested compounds as food and goes into attack mode. The body attacks itself, and health problems inevitably ensue.

And the dominoes keep falling. When the microbes can’t break down the food properly, they end up producing toxic chemicals instead of nutrients. Then, since the gut wall has become porous, those chemicals flow right into the bloodstream and get distributed throughout the body. Instead of being a source of nourishment, the digestive system becomes a significant source of toxicity in the body.

“A river of toxins flows from the gut into the blood, into the lymph and is then distributed all over the body,” says Campbell-McBride. “Once it gets in the brain, it causes gut and psychology syndrome.” The symptoms that manifest can be anything under the sun, says Campbell-McBride. “It could be a drop in blood-sugar level, a skin rash or a migraine. It could show up as cystitis or an asthma attack. It could be a panic attack. The symptoms can be immediate, or they can be delayed. On any given day, you have no idea what your body is reacting to. It can be reacting to a piece of lamb you just had for breakfast, plus a tomato you had yesterday, plus a banana you had a few days ago, plus something else you had two weeks ago.”

Ironically, even if someone has no discernible digestion issues at all, they could still be experiencing symptoms due to gut imbalance. “The majority of GAPS people have inflammation and ulcerations in their gut lining, whether or not they have digestive symptoms,” says Campbell-McBride. “It’s a whole long, long list of chronic degenerative diseases that people are suffering from nowadays because, from my point of view, every disease begins in the gut, and that’s where the treatment has to begin.”

The GAPS diet is designed to nourish the gut, heal the gut lining, seal the holes and rebalance the gut flora. Once that happens, the river of toxicity stops, the body cleanses itself and removes remaining toxins, and the immune system starts functioning the way it’s supposed to. Symptoms and conditions can fall away.

“We can influence the microbial community of our body through changing our diet,” she says. But it’s not worth trying to figure out which food has what effect. “As long as your gut lining is porous and leaky, you can presume you’re reacting to every morsel of food you eat,” she says. “Once all the holes are closed up and the gut lining has sealed itself, then foods digest properly before they absorb and food allergies and intolerances disappear.”

While the primary component of the GAPS protocol is the diet, it also includes a few food-based nutritional supplements and lifestyle changes.

As tempting as it is to consider the fallout of poor gut health as this person or that person’s problem, Campbell-McBride speaks of an emerging epidemic of illness. “There are hardly any healthy children nowadays in the Western world. Pretty much every child has got some kind of health problem,” she says. Certain statistics back up her claim. Studies conducted in the 1960s on the prevalence of autism in Europe and the U.S. reported two to four cases per 10,000 children. More recently, the CDC reported that, in 2016, approximately one in 54 children in the U.S. was diagnosed with an autism spectrum disorder (ASD). Campbell-McBride predicts that, in the next five years, half of all children born in English-speaking countries will be autistic.

For 10 years, Campbell-McBride has been training GAPS health practitioners all over the world, and, last year, she started training GAPS coaches who help people in a more hands-on way. She’s also developing a training program for professional chefs to learn to incorporate the GAPS protocol in their cooking. Campbell-McBride has authored three more books since 2004 on the topic and speaks about GAPS at conferences and seminars around the world.