Effects of Antacids on Pepsin
Background — Pepsin and Protein Digestion
In the human digestive system, there are many
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
functions to break proteins into smaller pieces called
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
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
Other cells in the stomach lining produce
(HCl), causing the stomach contents to have a
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
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
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
(pepsin, HCl, etc.). Once food is in the stomach, its presence there triggers
the release of the hormone,
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
do just what their name suggests: they
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
(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
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
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
- It is known that an acid environment is needed for proper absorption
of iron, calcium, and other minerals. How would neutralizing stomach
acid affect the absorption of these minerals? Could overconsumption of
antacids cause anemia? How much of the calcium in calcium-containing
antacids really is absorbed, given the more basic stomach environment
created by those antacids?
- One of the functions of the hydrochloric acid in our stomachs is to
kill harmful bacteria in our foods. Do antacid users have any greater
chance of food poisoning, Helicobacter, and/or other infections?
- Could overconsumption of antacids cause a deficiency of needed amino
acids due to inhibition of pepsin at higher pH levels?
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.
- 16 × 150 test tubes with caps
- wax pencil
- 1% pepsin solution (1 g pepsin in 100 mL or 10 g/L)
- boiled 1% pepsin solution
- 0.5% NaHCO3 (sodium bicarbonate — baking soda) (= 5 g/L)
- 0.1 M HCl (= 31.15 mL of conc. HCl/ gal or 8.24 mL/L of solution)
- hard-boiled egg white and knife
- antacid(s) of your choice (Students are invited to bring in samples from
home. Record which you use.)
- 250-mL beaker for each antacid sample
- pH paper or pH meter
- Obtain eight 16 × 150 test tubes and
number them. Obtain an additional test tube for each antacid you plan to
- In these tubes place the following
§ 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.
(@ body temp
||*boiled pepsin soln.
||keep @ room temp
||§ 5 mL w/ antacid(s)
- Mix each solution with a vortex.
(or a pH meter) to determine the pH of each test tube and record the pH
values in your lab notebook.
- In a 250-mL beaker, obtain 100 mL of
0.1 M HCl. Determine the pH of this solution and record in your lab
- 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.
- 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
- Obtain “fingernail-sized” slices of
egg white and add one piece to each test tube.
- Cap the tubes and incubate all
EXCEPT #8 at 37° C for 48 hr. Store #8 at room temperature in the
- 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?
- To compare your data to those
collected by other students here at UC, you may fill in the chart below and
submit your data.
- 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.
- 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.
- 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:
|3||no egg white observed, nothing left, completely gone|
|2||some egg white present but decreased mass and very transparent|
|1||egg white slightly transparent and only slightly changed in size|
|0||no change in the condition of the egg white|
- What effect(s) does pH have on
pepsin’s ability to digest egg white?
- 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.
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