Stomach acid and pepsin work together at the beginning of protein digestion. The acid creates the environment pepsin needs; pepsin is the enzyme that starts cutting dietary proteins into smaller pieces. Dr. Natasha Campbell-McBride gives this first step particular attention in Gut and Physiology Syndrome.[1]
These names can sound like different ways of saying “digestive enzymes.” They describe different things. Understanding the difference makes the rest of the GAPS digestion chapters much easier to follow.
What Acid Does and What Pepsin Does
| Part | Its Role |
|---|---|
| Hydrochloric acid | Creates the acidic stomach environment and helps activate protein-digesting enzymes. |
| Pepsin | Begins breaking dietary proteins into smaller peptide chains. |
| Pancreatic and intestinal enzymes | Continue the digestive work after food leaves the stomach. |
The book gives a stomach pH of 3 or below for pepsin to work properly. A lower pH number means greater acidity. Low acid production is called hypochlorhydria; it can leave the stomach environment less suitable for pepsin’s work.[1]
Digestion Continues After the Stomach
Food passes from the stomach into the duodenum, the first part of the small intestine. Pancreatic juices and intestinal enzymes continue breaking down food there. Healthy cells lining the intestine, called enterocytes, have brush-border peptidases that help finish peptide breakdown before absorption.[1]
That gives you a useful order: stomach digestion, further digestion in the small intestine, then the work of the intestinal lining. A peptide is a short chain of amino acids. Reaching the peptide stage does not mean the entire digestive job is finished.
The DPP-IV and peptidase guide explains the later enzyme step. Keeping it separate from pepsin helps you see why GAPS addresses more than the stomach alone.
Why the Small Intestine Neutralizes Acid
The stomach and small intestine need different conditions. The book explains that pancreatic bicarbonate neutralizes acid arriving with food so pancreatic enzymes and bile can do their work in a more alkaline environment.[1]
Secretin and cholecystokinin, or CCK, help coordinate this response. Acid is important for secretin release. Products of fat and protein digestion also stimulate CCK; human feeding research has demonstrated that response.[2] Low stomach acid should not be described as switching off every pancreatic or bile response.
For the separate jobs of these hormones, use our secretin and CCK guide. The practical distinction is that an acidic stomach and a less acidic small intestine are both part of digestion.
Where Gluten and Casein Enter the Discussion
Campbell-McBride uses gluten and casein as extensively studied examples of proteins that may remain incompletely digested in the GAPS account. She discusses opioid-like peptides from these proteins and their proposed effects on the nervous system.[1]
Those consequences belong in the low-acid and peptides guide. Here, the point is the normal sequence: a protein begins being broken down in the stomach, and several later steps still follow.
Why One Enzyme Does Not Replace the Whole Process
The book gives stomach acidity priority in its supplement discussion. It also permits a pancreatic preparation when it genuinely helps and its ingredients fit the diet. These are parts of a larger approach that includes food changes, the gut flora and the intestinal lining.[1]
Her later discussion connects impaired digestive responses with pancreatic and bile problems. The gallstones and pancreatic-enzyme guide covers that clinical context, rather than turning this explanation of normal digestion into a way to diagnose a painful condition.
Put the Terms Beside the Product
Our family uses digestive enzymes, and I find it useful to keep the preparation itself clear when discussing the books. “Acid support,” “pepsin” and “pancreatic enzymes” do not describe interchangeable products. Our family’s use does not establish a dose for someone else.
The digestive-support overview puts those categories together. If you need the author’s actual capsule passage, the Betaine HCl and pepsin guide keeps its amounts and timing in one place.
The Supplement Introduction Tracker is listed in my WFLI Shop for keeping product names, amounts and response notes together.
For what happens after absorption, the blood and lymph guide follows nutrients from the intestinal lining into circulation.
References
- Campbell-McBride, N. Gut and Physiology Syndrome (2020), “Digestive Enzymes,” stomach acid and pancreatic enzymes; protein-digestion and enterocyte discussion.
- Liddle, R. A., et al. Cholecystokinin bioactivity in human plasma: molecular forms, responses to feeding, and relationship to gallbladder contraction. Journal of Clinical Investigation 75 (1985): 1144–1152. DOI:10.1172/JCI111809.
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