Effects of Antacids on Pepsin

Background — Pepsin and Protein Digestion

In the human digestive system, there are many enzymes to help digest our food. In the mouth, salivary amylase acts to break long starch molecules into maltose, a disaccharide. In the stomach, the enzyme pepsin functions to break proteins into smaller pieces called polypeptides. Because pepsin can only break the bonds next to certain amino acids, proteins are only broken into these shorter chains, and not digested all the way to amino acids. That must be done later, in the small intestine. Most digestion and absorption of nutrients occurs in the small intestine. A number of enzymes including maltase, sucrase, and lactase (which break down the corresponding disaccharides), trypsin and chymotrypsin (which further digest polypeptides to amino acids), and pancreatic lipase (which breaks fats into glycerol and fatty acids) are secreted by the pancreas into the small intestine. While not an enzyme but an emulsifying agent, bile is secreted by the gall bladder into the small intestine. All these, plus some enzymes secreted by the intestinal lining work to digest the food we eat.

So that pepsin doesn’t digest the cell that makes it, it is synthesized and secreted in an inactive form called pepsinogen. Other cells in the stomach lining produce hydrochloric acid (HCl), causing the stomach contents to have a pH of around 1 to 3. Since the pepsinogen and hydrochloric acid are secreted by different cells, they don’t come into contact with each other until they meet in the stomach cavity. Pepsinogen needs the low stomach pH and hydrochloric acid for conversion to pepsin. Once some of the pepsinogen is converted, that starts a chain reaction because pepsin can also trigger formation of more pepsin. This, by the way, is an example of a positive feedback loop (Campbell, 1987). This acidic pH range is also necessary for proper functioning of the pepsin: a pH of 2 is optimum for pepsin function (Campbell, 1987). Thus, it would be suspected that anything which changes stomach pH might interfere with both formation and effectiveness of pepsin.

One thing that can denature proteins, including enzymes, is a change in pH, and in the case of enzymes, this would cause them to cease functioning. While hydrochloric acid, itself, cannot break peptide bonds (Cunningham, 1989), the low pH in the stomach denatures proteins in food, thereby changing their shape and exposing their peptide bonds so that pepsin can break these bonds. Even left-over salivary amylase is denatured, ceases to work, and is digested (Campbell, 1987). While hydrochloric acid does not actually digest food, it does help by softening the “glue” between the cells of various foods, making those foods more vulnerable to digestion by pepsin. Hydrochloric acid also helps by killing bacteria that are swallowed with food (Campbell, 1987).

The smell and/or taste of food triggers an initial burst of gastric juice (pepsin, HCl, etc.). Once food is in the stomach, its presence there triggers the release of the hormone, gastrin into the blood system. As this hormone recirculates to the stomach, it stimulates continued production of gastric juice. The presence of food dilutes the hydrochloric acid, so stomach pH is a little higher when food is present, stimulating the secretion of more gastric juice. As the stomach gradually empties, the pH decreases. If the pH of the stomach becomes too low, that inhibits secretion of gastrin, thus reducing the secretion of gastric juices. This is an example of a negative feedback loop (Campbell, 1987), one of the many involved in homeostasis.

Antacids do just what their name suggests: they neutralize the normal stomach acid (HCl), causing the pH to rise to a nearly neutral pH of around 6 to 7. As the pH rises above 4, pepsin activity decreases or stops. Some types of antacids, made of sodium bicarbonate (NaHCO3) or calcium carbonate (CaCO3), are easily absorbed into a person’s body and can cause a pH imbalance, possibly leading to kidney damage or other problems (Berkow, 1987). Using negative feedback loops as mentioned above, the body attempts to keep the pH level of the stomach fairly constant, and thus it has been shown that for many people, consumption of antacids actually increases the amount of acid secreted in an effort to restore normal pH. One source states that antacids neutralize the stomach acid, preventing proper digestion and interfering with absorption of nutrients, thereby leading to continued indigestion. This source further states that antacids are useless for gas and bloating, and that CaCO3 antacids can cause a rebound effect in which the stomach produces more acid than before, once the antacid’s effects wear off (Balch and Balch, 1997). There also have been cases of people with self-diagnosed “heartburn” who really were on the verge of a heart attack, who should have been going to the emergency room instead of popping antacids. Thus, while consumption of antacids may be necessary when prescribed by a doctor to treat gastric ulcer, casual use is probably not a good idea. Just because they are “over-the-counter” drugs does not mean they are harmless.

Some other related issues to consider:

Upset Stomach:
While there are legitimate reasons why a doctor might prescribe antacids in specific cases (ulcers), there are other, safer ways of settling an upset stomach due to things like morning sickness, motion sickness, flu, or too many hot dogs. No amount of antacids nor home remedies can cure “stomach aches” that really are heart attacks or food poisoning, and these problems require immediate medical attention. If in doubt, go see a doctor! A number of herb books suggest ginger for indigestion, morning sickness, motion sickness, nausea, and vomiting. Even here, though, don’t overdo it because even ginger can cause stomach distress if taken in large quantities (Balch and Balch, 1997). A “pinch” (⅛ tsp or less) of ginger can be placed into a cup of water, and the whole thing heated in a microwave as though making a cup of tea. This is then sipped slowly. I personally saw someone who had the flu, had been vomitting, and was “white as a sheet,” take some ginger in this manner, and within about 15 min, return nearly all the way to normal. If someone must have a simultaneous sugar fix, gingerale that contains some real ginger may be used, and the carbonation often also helps calm an upset stomach.
Dietary Calcium:
Recently, one manufacturer of over-the-counter antacids has been advertizing their product as a source of dietary calcium. This raises a number of important questions to consider. Is a shortage of dietary calcium a problem? How much does a person need and how much are you getting from your normal diet? How do you know when you need a supplement? Is there such a thing as too much calcium, and what effects would that have? Is an antacid really the best way to get calcium? (Calcium is absorbed best at an acidic, not neutral, pH.) What dietary sources of calcium are there, and how many of them do you consume (how often)? Many authors recommend 1200 to 1500 mg of calcium a day, especially for women. Do you drink milk? Do you eat dark green leafy vegetables?
Over-consumption of calcium-alkali antacids can lead to hypercalcemia, which can adversely affect a number of organ-systems, including the kidneys, bones, muscles, and pancreas (Berkow, 1987). Calcium, like iron, needs an acidic environment for proper absorption (Weed, 1992). Many sources point out that too much dietary phosphate (PO4), as in soft drinks, will leach calcium from the bones. Good dietary sources of calcium include dairy products (milk, yogurt, etc. – 4 cups of milk a day will give most people an adequate amount of calcium, plus the proper amount of vitamin D needed to handle it), fish bones (sardines, salmon, smelt), collard greens, spinach, broccoli, tahini, tofu (if calcium is added to the liquid), oats and oatmeal, seaweed, and dandelion leaves (Postlethwait and Hopson, 1989; Weed, 1992). One source suggests soaking clean egg shells or bones in vinegar or lemon juice (which will dissolve the calcium), then using that vinegar on salads and/or in cooking (Weed, 1992). If needed, supplements that include bone meal, oyster shell, dolomite, or calcium orotate are available (Fredericks, 1976), and these are not designed to simultaneously inhibit pepsin’s ability to digest the protein in one’s diet.
Food Allergies:
Amino acids, dipeptides, and tripeptides (two or three amino acids stuck together) are normally absorbed through the intestinal walls. Polypeptides and protein molecules generally are not absorbed in this manner, but occasionally larger polypeptides do cross the intestinal wall, and this may lead to allergic reactions. In babies, some absorption of whole proteins does occur, and may help transfer antibodies from the mother’s milk to provide passive immunity (Weinreb, 1984). Here, then, is a question to consider: if antacids interfere with pepsin’s ability to digest proteins, and if indeed, many food allergies stem from partially- or undigested proteins being absorbed through the intestinal walls, could antacid-induced inhibition of protein digestion increase the chances of developing food allergies?
Vitamin Pills:
Some people claim it doesn’t do any good to take vitamin pills. They say our bodies don’t digest the pills, which are supposedly eliminated, whole. As evidence, these people drop a vitamin pill into a solution of HCl, then point out that the tablet does not dissolve there. Many of these tablets use a starch or stearate binder to hold them together, and some have a light protein coating on the outside to seal them. Based on the information on HCl cited above, what might be wrong with these people’s experimental design – what might be missing from their mixture?
Other Questions:
Here are some other questions and concerns to think about that relate to antacid consumption.


Balch, James F. and Phyllis A. Balch. 1997. Prescription for Nutritional Healing, 2nd Ed. Avery Publ. Group, Garden City Park, NY.

Berkow, Robert, ed. 1987. The Merck Manual. 15th ed. Merck, Sharp and Dohme, Rahway, NJ.

Campbell, Neil A. 1987. Biology, 1st Ed. Benjamin/Cummings Publ. Co, Inc. Menlo Park, CA.

Cunningham, John D. 1989. Human Biology. Harper & Row Publ. Co., New York, NY.

Fredericks, Carlton. 1976. Dr. Carlton Fredericks’ New & Complete Nutrition Handbook. Nutri-Books Corp. Denver, CO.

Postlethwait, John H. and Janet L. Hopson. 1989. The Nature of Life. Random House Publ. New York, NY.

Weed, Susun S. 1992. Menopausal Years the Wise Woman Way. Ash Tree Publ, Woodstock, NY.

Weinreb, Eva Lurie. 1984. Anatomy and Physiology. Addison-Wesley Publ. Co. Menlo Park, CA.

Materials Needed


  1. Obtain eight 16 × 150 test tubes and number them. Obtain an additional test tube for each antacid you plan to test.
  2. In these tubes place the following solutions:
    0.5% Baking
    Hydrochloric Acid
    1% Pepsin
    Other Info/Ingredients
    (@ body temp
    unless noted)
    1 10 mL        
    2 5 mL     5 mL  
    3 5 mL 5 mL      
    4 5 mL   5 mL    
    5   5 mL   5 mL  
    6     5 mL 5 mL  
    7     5 mL 5 mL* *boiled pepsin soln.
    8     5 mL 5 mL keep @ room temp
    9+       5 mL § 5 mL w/ antacid(s)
    § For #9, etc., 100 mL of HCl should be mixed with one “dose” of antacid. 5 mL of that should be used. See directions below.
  3. Mix each solution with a vortex.
  4. Use pH paper (or a pH meter) to determine the pH of each test tube and record the pH values in your lab notebook.
  5. In a 250-mL beaker, obtain 100 mL of 0.1 M HCl. Determine the pH of this solution and record in your lab notebook.
  6. To this solution, add one dose of the antacid you are testing (if more than one brand of antacid is being tested, each sample needs a separate beaker of solution). If needed, use a mortar and pestle to crush tablets. Stir to completely dissolve and mix. Determine the new pH reading and record in your lab notebook.
  7. For each antacid you are testing, label a test tube (#9, #10?, etc.), and place 5 mL of the solution you just mixed + 5 mL of 1% pepsin solution into that test tube. Check the pH again. Remember to record tube number(s), contents, and pH in your lab notebook.
  8. Obtain “fingernail-sized” slices of egg white and add one piece to each test tube.
  9. Cap the tubes and incubate all EXCEPT #8 at 37° C for 48 hr. Store #8 at room temperature in the designated location.
  10. The next class period, obtain your tubes and record what happened in each. Is there egg white still present or not? Is it still white or translucent? Is it still in one piece or broken up? Is there any smell or any other change?
  11. To compare your data to those collected by other students here at UC, you may fill in the chart below and submit your data.
  12. CLEAN UP AFTER YOURSELF!!! Using hot, soapy water, thoroughly clean all equipment. Do not leave pieces of egg white in the sinks. Remove them and put them in the trash.
  13. Make sure that you have recorded all data and observations into your lab notebook. Take any other notes you feel are important. Draw any new equipment so you can better remember what it looks like and how to use it.
  14. When everyone has submitted their data online, you may view and print class data. As you compare the class data, you may wish to comment on the implications, healthwise, for someone who consumes a lot of antacids.


The following rating system may be used to indicate the results of this experiment:
3no egg white observed, nothing left, completely gone
2some egg white present but decreased mass and very transparent
1egg white slightly transparent and only slightly changed in size
0no change in the condition of the egg white

Create a table in your notebook similar to the following: Then, please fill in the following data and submit the form.

Tube # Contents pH Reaction
1 10 mL dH2O
2 5 mL dH2O + 5 mL 1% pepsin solution
3 5 mL dH2O + 5 mL 0.5% NaHCO3
4 5 mL dH2O + 5 mL 0.1 M HCl
5 5 mL 0.5% NaHCO3 + 5 mL 1% pepsin solution
6 5 mL 0.1 M HCl + 5 mL 1% pepsin solution
7 5 mL 0.1 M HCl + 5 mL BOILED 1% pepsin solution
8 5 mL 0.1 M HCl + 5 mL 1% pepsin solution (RT)
9 5 mL Rolaids® solution + 5 mL 1% pepsin
10 5 mL Tums® solution + 5 mL 1% pepsin
11 5 mL Mylanta® solution + 5 mL 1% pepsin
12 5 mL Pepto-Bismol® solution + 5 mL 1% pepsin
13 5 mL Maalox® solution + 5 mL 1% pepsin

 Submit  Reset 

View Class Data


  1. What effect(s) does pH have on pepsin’s ability to digest egg white?
  2. What effect(s) does the addition of antacid have on pH and on pepsin’s ability to digest egg white? Of what significance would this be in “everyday life?”

Copyright © 1998 by J. Stein Carter. All rights reserved.
This page has been accessed Counter times since 18 Jan 2003.