As Hippocrates said, «all disease begins in the gut». If the digestive system is working efficiently and effectively, the individual generally enjoys robust health. Unfortunately, most people suffer from at least some form of impaired digestion. In this newsletter, Part 1 of our Digestion Series, we will examine the core components of the digestive system. In Part 2, we will look at specific foods, herbs, and lifestyle choices that either strengthen or weaken digestion.
It’s often been said that you are what you eat. While this is true, it’s more accurate to say you are what you are able to digest. In other words, two people can eat the exact same foods, but if person A’s digestive system is impaired, those foods could weaken his/her gut, thereby weakening his/her immune system and potentially contributing to more serious conditions. On the other hand, if person B’s digestive system is strong, he/she would optimize the extraction of the foods’ nutrients while efficiently eliminating all waste products.
Digestion begins even before food enters the mouth. The very smell of food triggers the production of digestive enzymes, particularly in the saliva. Digestive enzymes are complex proteins that breakdown food into its core components. The efficacy of enzymes is intimately related to pH, which we’ll explore below when discussing stomach acid. There are three general classes of digestive enzymes:
The pancreas is the primary source of digestive enzymes, although they also occur in the saliva and in uncooked foods. The particular enzyme contained in saliva is called amylase, which helps break down carbohydrates. The quantity of salivary amylase differs greatly between individuals, based on the following lifestyle and genetic factors:
Whereas salivary amylase is an important source of enzymes, the pancreas, as mentioned above is the enzymatic powerhouse. The primary function of the pancreas is to create «exocrine» enzymes for the digestion of food. The organ’s secondary function (though no less important) is to create «endocrine» hormones used to regulate metabolism. These hormones include insulin, glucagon, somatostatin, and gastrin.
Regarding exocrine enzymes, the pancreas creates:
The content of pancreatic fluid varies based on many factors, particularly age and diet. In general, pancreatic secretion levels decrease as we age.4 In one study, for example, researchers observed pancreatic enzyme levels among elderly people to be approximately 60% those of young adults.5 As we age, therefore, we are more likely to require digestive enzyme supplements (discussed below).
Regarding diet, a low-carbohydrate diet tends to promote increased pancreatic enzymes compared to a low-fat diet. In one study, researchers measured postprandial and inter-digestive enzyme levels of subjects following either a low-carb or low-fat diet for four weeks. Inter-digestive enzyme levels were 4 times higher in the low-carb group compared to the low-fat group. Moreover, postprandial enzyme levels (a measure of digestive response) were twice as high in the low-carb group compared to the low-fat group.6
With respect to effective, efficient digestion, gastric secretions are just as important as pancreatic enzymes. Gastric secretions can be grouped into four basic categories:
Mucus cells are the most abundant epithelial cells. They cover the entire surface of the gastrointestinal tract and are extremely important with respect to gut permeability (described below).
Gastrin is the principal hormone contained in gastric secretions. Its job is to stimulate the secretion of HCl, also known as gastric acid.7 HCl is extremely important with respect to breaking down protein molecules, activating important enzymes and hormones, and protecting against bacterial overgrowth in the gut.8 Increased HCl, for example, protects against orally ingested pathogens.9 At the same time, depressed HCl levels promote small intestinal bacterial overgrowth (SIBO).10
Achlorhydria (the complete absence of stomach acid) and hypochlorhydria (low stomach acid) are common digestive problems. The most common cause of both conditions (discussed in Part 2 of this series) is improper diet, particularly excessive consumption of sugar and, more generally, adherence to a high-carbohydrate diet.
Besides diet, ageing also promotes decreased HCl. In one study, 30% of Americans over the age of 60 were observed to suffer from atrophic gastritis, a condition characterized by chronic inflammation of the stomach mucosa and achlorhydria (or extremely low stomach acid secretion).11
When gastric acid is too low, food is improperly absorbed. This means that undigested and/or partially digested food particles are able to access the digestive tract. If allowed to persist, this condition can lead to food sensitivities and food allergies in the short-term, and chronic conditions like gastroesophageal disease (GERD) and irritable bowel syndrome (IBS) in the long-term.
Conventional allopathic medical wisdom would have us believe that heartburn is the result of elevated stomach acid. If this premise were true, then all infants and babies should suffer from heartburn because they have relatively higher amount of HCl compared to adults. In fact, the opposite of the premise is true. Heartburn/acid reflux results from a combination of insufficient HCl and bacterial overgrowth in the stomach and intestines.
As mentioned above, the fourth type of gastric secretion is pepsin. There are three principle proteases (enzymes involved with the digestion of protein):
As mentioned above, the pancreas is responsible for trypsin and chymotrypsin. Pepsin, on the other hand, is produced in the stomach and is dependent on adequate HCl levels. Pepsin’s precursor is pepsinogen, a molecule secreted by «chief cells» along the stomach wall. When pepsinogen mixes with HCl, it converts into activated pepsin.12
As you can see, gastric acid (HCl) is critical to proper digestion. In Part 2, we will discuss dietary and nutritional strategies for improving digestion, particularly by increasing HCl.
Gut microbiome is a blanket term that refers, collectively, to the trillions of microorganisms that inhabit the gastrointestinal tract. This includes up to 1,000 different bacterial species, which encode 5 million different genes, and encompass around 30 to 40 trillion cells.13, 14 The gut microbiome fulfills numerous critical functions, including the following, and more.15, 16, 17
What constitutes a healthy gut microbiome? In short, diversity — the greater the number of different species of microorganisms inhabiting the microbiome, the better it performs. In recent years, scientists have demonstrated that people living in contemporary urban environments have far less diverse gut microbiomes compared to those of our ancestors, as typified by various modern hunter-gatherer tribes.
For example, in 2015, researchers analyzed gut microbiome samples from an «isolated Yanomami Amerindian village with no documented previous contact with Western people». Among these people, the researchers observed the «highest diversity of bacteria and genetic functions ever reported in a human group».18
For another study, in 2013, researchers analyzed the Hadza, a group of traditional hunter-gatherers living in modern-day Tanzania. The Hadza were reported to «have higher levels of microbial richness and biodiversity [compared to] Italian urban controls».19
So what determines the composition of one’s gut microbiome? Many factors are important, including age, genetics, environment, and lifestyle. The most important and influential factor, however, according to research published in the British Medical Journal, is diet.20
In Part 2, we’ll explore which foods influence the gut microbiome, as well as which nutritional supplements are useful in making it stronger and more robust.
Our final topic, with respect to digestion, is gut permeability. The intestinal mucosal barrier covers a surface area of approximately 400m2 and utilizes around 40% of the body’s energy expenditure.21 Ideally, this lining prevents antigens, undigested or partially digested food molecules, and other harmful microorganisms from entering the bloodstream. Concurrently, the intestinal lining allows nutrients and other beneficial molecules to pass into the blood stream.
Gut permeability, also known as «leaky gut», is an increasingly common condition whereby the intestinal lining becomes compromised, thereby allowing harmful particles to access the body. There is a growing body of evidence demonstrating that gut permeability can cause or exacerbate many diseases, including autoimmune diseases such as inflammatory bowel disease, celiac disease, autoimmune hepatitis, type-1 diabetes (T1D), multiple sclerosis, and systemic lupus erythematosus (SLE).22
So what causes gut permeability? One of the biggest culprits is a weakened gut microbiome (decreased diversity). Other contributing factors include, excessive alcohol consumption, and excessive consumption of gluten-containing cereals, sugar, and hydrogenated fats.23, 24
The old adage that you are what you eat lends itself to an extremely simplified, and perhaps detrimental, view of digestion. As we have seen, digestion is an extremely intricate process, involving and depending upon, among other things, digestive enzymes (from the pancreas, saliva, and gastric secretions), hydrochloric acid, and gut microbiome health. Having explored the science behind digestion, in Part 2, we’ll examine dietary, nutritional, and lifestyle practices that reliably strengthen digestion, thereby enabling us to maximize the assimilation of nutrients, protect our immune systems, and enjoy heightened vitality, mental clarity, and overall wellbeing.