Coffee and the Stomach: A Challenge to Study

Ildi Revi
A discussion of the literature, by Ildi Revi, Director of Coffee

A key dialogue that would be valuable for the Coffee Council brain trust to explore together is the connection between coffee and gastrointestinal issues.

Some people drink a cup of coffee and they don’t feel well afterward, get indigestion, or have acid reflux. Observation tells us that this is not uncommon. Doctors frequently advise their patients to regulate coffee use if they are having gastric symptoms. What scientific evidence is the basis for this advice? Is coffee’s acidity the culprit? Why do some people feel coffee is too “harsh” for their stomachs? Has science actually demonstrated an effect of coffee on stomach issues? Is there research that has established a link between coffee and stomach ailments? What sort of coffee may be advisable for people who have a sensitivity to coffee? I delved into some of the scientific literature to find answers, bust myths and narrow down areas of study for the Coffee Council.

The cliff notes to this story are that the most current and overarching scientific evidence points to coffee consumption having little or no significant relationship with any of the major acid-related upper gastrointestinal disorders, including different types of ulcers and reflux <1>. However, there is a much more complex narrative to tell, and we cannot discount the experiences of our patients and clients.

Here is a summary of what I found:

Is it really the acidity and caffeine in coffee that hurts the stomach?

This is a common complaint and an important one to look at directly. Coffee has a pH between 4.8 and 6.0, with a very small buffering capacity or titratable acidity. That means that coffee has a lower acid content, on average, than tomato or orange juice. This pH actually translates to a level of acidity not that much different from our saliva or milk which both are at around a pH of 5.5. This makes the acidity of coffee very unlikely to affect stomach ailments or cause any real difference in stomach acid.

Regarding caffeine, studies have shown that coffee’s effects on the stomach are present with both regular and decaffeinated coffee, and thus not by caffeine alone <2>. This tells us that something else may be leading to or exacerbating stomach symptoms.

What other compounds in coffee may influence gastric issues?

What is important to note is that the scientific evidence for possible coffee components affecting gastric acid secretion in humans is still very scarce. We are learning that the real culprit of gastric acid production may be not acid or caffeine, but other compounds entirely. Evidence is pointing to the likelihood that there are other compounds linked to a chemical signaling in our bodies that tells our stomachs to produce gastric acid. These compounds include (β) N-alkanoyl-5-hydroxytryptamides and chlorogenic acids <3-6>. Organic acids common to coffee, especially malic acids, have also been shown in other beverages, such as wine, to stimulate gastric acid production <7>.

Another relatively new hypothesis is related to our mouth signaling to our stomach via our taste buds. One recent study demonstrated that caffeine ingestion actually stimulated bitter taste receptors in the mouth and stomach, which led to a signal to produce gastric acid <8>. This is an example of the variety of complex methods to signal our stomach into action.

There is relatively new research that shows certain compounds naturally occurring in coffee can prevent gastric acid secretion in the stomach <6, 9-10>. One notable compound, N-methylpyridinium (or NMP, for short), has been identified as actually down-regulating gastric acid production. This means that there are certain compounds in coffee that could limit this irritating stomach acid. If a coffee variety or roast level allows more of them, it may contribute less to stomach issues.

One study showed that when the NMP content in coffee was higher and the βN-alkanoyl-5-hydroxytryptamides and chlorogenic acid content was lower, there was less stomach acid produced by the study participants <10>. So, while NMP is a key compound in the search for a coffee that doesn’t cause symptoms, the presence of other compounds also could potentially have an effect.

Another study concluded that a darker roasted blend did not stimulate gastric acid secretion in healthy volunteers as compared to a lighter roast market-blend beverage <11>. However, the research on the complex mixtures, relative abundances, and combinations of these and other potentially gastric-acid-regulating compounds is still very sparse, and only a couple of studies have investigated this topic.

As the Director of Coffee, I would like more information on how to craft (choose advantageous green coffee and roast it to an advised level) the perfect “stomach friendly” coffee. I would like to explore targeted processes to develop that maximize the amount of gastric acid reducing compounds in coffee, while minimizing the compounds that promote it. Today, though, we do not appear to have the level of scientific understanding of these chemical compounds and their impact on the human body.

Studies about Heartburn and Reflux

Heartburn is the most frequently reported gastric symptom reported after the consumption of coffee. Nevertheless, the scientific evidence on whether drinking coffee causes heartburn or irritates reflux disorders is mixed. One review of the literature concluded that coffee does not contribute to reflux <12>. Although the effects of coffee on reflux are not profound or extensive, other evidence suggests that coffee could affect this issue.

If the acidity of coffee is not to blame for stomach related ailments, some scientists currently believe the reason behind reported irritation may be enhanced gastric acid production in the stomach <12-13>. There is a growing amount of research devoted to identifying which compounds in coffee could be responsible for this promotion of gastric acid secretion and exactly how this happens. I will go over this in a minute.

One study found that coffee precipitated heartburn in about 68% of patients with daily symptoms <13>. In people who already identify as “coffee sensitive” the results may even be stronger. One such study found that different coffees induced various levels of reflux in a “coffee-sensitive” study group, and demonstrated that symptoms were more severe if they had a meal afterward <14>. These studies, although limited, may indicate that certain coffee consumers may be more sensitive than others to stomach-related effects, which partially explains why study results on this topic have been inconclusive.

Gastro esophageal reflux disease (GERD) is a specific reflux condition caused by return of stomach acid into the esophagus. Common causes of this condition are the consumption of spicy or fatty food and overeating <7>. Coffee has been suggested as a possible cause in some cases, however there is no evidence that coffee consumption affects the symptoms of this disease <15>. Those who suffer from symptoms often self-regulate their diet according to their own sensitivities and some people may choose to limit their coffee consumption based on misconceptions of the beverage and its effect on the body.

A study by Nilsson and others (2004) found something different. Their research shows an inverse relationship between drinking coffee and risk of reflux, meaning that people who drank coffee were less likely to experience reflux. The same study found that other healthy lifestyle factors, such as eating a high fiber diet and exercise, also had fewer reflux issues, pointing out how drinking coffee can be an important part of a healthy lifestyle <16>.

Still, the problem isn’t so clear-cut because of conflicting evidence and significant differences within different coffees. In fact, there are no one large, well-designed study that shows that the elimination of coffee or caffeine consistently improves reflux symptoms or outcomes.

How does coffee impact peptic ulcers?

Peptic ulcers are lesions that develop in the mucosa of the stomach wall causing pain and discomfort. A meta-analysis from 2013 analyzed whether various types of ulcers could detect any association of coffee consumption with either gastric ulcers or duodenal ulcers. Previously, coffee had been linked with the development of peptic ulcers, but the researchers concluded there was no significant relationship between coffee consumption and the four major acid-related upper gastrointestinal disorders.

Today, studies investigating the risk factors for the development of stomach ulcers conclude that coffee is no longer considered a risk factor <17,18>. Therefore, even though coffee may stimulate gastric acid secretion, and is often blamed for gastric symptoms, including ulcers, there is no good scientific evidence that firmly links coffee consumption with peptic ulcers.

Does coffee cause indigestion?

Although coffee is often mentioned as a cause of indigestion symptoms, the research on this topic shows little association between coffee and dyspepsia <17>. Many food items, along with coffee, have been alleged to aggravate dyspeptic symptoms, but a relation between them and dyspepsia remains to be confirmed <12>.

Since it is a common belief that coffee-drinking induces intestinal distress, the effect of coffee and caffeine has on the small bowel transit and fluid secretion has also been studied. In the multiple studies I looked at, none have found a decrease in intestinal “transit time” <18,19>, and no data are available that support an effect of coffee on small intestinal transit. It seems there is no scientific consensus (or any evidence at all, that I could find) that shows a link between drinking coffee and intestinal distress.

If someone is experiencing indigestion after drinking coffee, what else might be going on? What may be a part of a morning coffee routine that does not agree with the body? Are sweeteners or creamers to blame? Is the coffee the highest quality, clean, organic coffee from a trusted company?

What else in coffee could be contributing to gastrointestinal troubles?

Are there toxins in the coffee? Could they be affecting the stomach? Molds, such as the Aspergillus or Fusarium species may be to blame. Both of these are commonly identified in low-quality, poorly processed coffee <22>. Ingesting mold and moldy foods is known to cause a variety of adverse health effects, including stomach pain, acid reflux, and indigestion. Many fungi produce metabolites called mycotoxins, which are known to be common in poor quality coffees, too. Ochratoxin A is a known fungal-related toxin in coffee <23> which has various ill-effects on human health.

Pesticide residues, if they remain on coffee, could also contribute to stomach troubles. There are various stomach and digestive-related symptoms which are related to acute pesticide poisoning. However, these symptoms are usually expected in high-exposure (poisoning) situations. This doesn’t mean that pesticide residues cannot irritate your stomach, but this is a challenging topic to study, and therefore more research is needed in this area.

In summary, the Research shows:

  1. Overall, coffee has been predominately exonerated from blame for most common stomach complaints. Although frequently mentioned by patients, there is little or no evidence for an association of coffee ingestion with peptic ulcer disease or functional dyspepsia <1, 12>.
  2. Some chemical compounds naturally found in coffee may stimulate gastric acid production. This may irritate certain gastrointestinal issues, such as reflux, but the research results on this topic are mixed.
  3. Coffee may stimulate digestion. Scientists have linked coffee drinking to enhanced colonic motor activity and gallbladder contraction <20-21>. They found that coffee elicits this response in under 4 minutes, which means that such a mechanism could be mediated by neural mechanisms or by gastrointestinal hormones.

What might be brewing along with your coffee that contributes to stomach symptoms? A Coffee Council working group could contribute significantly to this topic, and bridge the gap from research into a roasted coffee that is more stomach friendly. This could improve the quality of life of many people.

References:
  1. Shimamoto, T.; Yamamichi, N.; Kodashima, S.; Takahashi, Y.; Fujishiro, M.; Oka, M.; Mitsushima, T.; Koike, K., No Association of Coffee Consumption with Gastric Ulcer, Duodenal Ulcer, Reflux Esophagitis, and Non-Erosive Reflux Disease: A Cross-Sectional Study of 8,013 Healthy Subjects in Japan. PLoS ONE 2013, 8 (6), 1-9.
  2. J. Boekema, M. S. G. P. v. B. H. A. J. P. M. S. P., Coffee and Gastrointestinal Function: Facts and Fiction: A Review. Scandinavian Journal of Gastroenterology 1999, 34 (230), 35-39.
  3. Wendl, B.; Pfeiffer, A.; Pehl, C.; Schmidt, T.; Kaess, H., Effect of decaffeination of coffee or tea on gastro-oesophageal reflux. Alimentary Pharmacology & Therapeutics 1994, 8 (3), 283-287.
  4. Ehrlich, A.; Lücker, P. W.; Schaefer, A., Effect of processed and non-processed coffee samples on gastric potential difference. Study with healthy male Helicobacter pylori-positive and Helicobacter pylori-negative volunteers. Arzneimittel-Forschung 1999, 49 (7), 626-630.
  5. Lang, R.; Bardelmeier, I.; Weiss, C.; Rubach, M.; Somoza, V.; Hofmann, T., Quantitation of βN-Alkanoyl-5-hydroxytryptamides in Coffee by Means of LC-MS/MS-SIDA and Assessment of Their Gastric Acid Secretion Potential Using the HGT-1 Cell Assay. Journal of Agricultural and Food Chemistry 2010, 58 (3), 1593-1602.
  6. Weiss, C.; Rubach, M.; Lang, R.; Seebach, E.; Blumberg, S.; Frank, O.; Hofmann, T.; Somoza, V., Measurement of the Intracellular pH in Human Stomach Cells: A Novel Approach To Evaluate the Gastric Acid Secretory Potential of Coffee Beverages. Journal of Agricultural and Food Chemistry 2010, 58 (3), 1976-1985.
  7. Liszt, K. I.; Walker, J.; Somoza, V., Identification of Organic Acids in Wine That Stimulate Mechanisms of Gastric Acid Secretion. Journal of Agricultural and Food Chemistry 2012, 60 (28), 7022-7030.
  8. Liszt, K. I.; Ley, J. P.; Lieder, B.; Behrens, M.; Stöger, V.; Reiner, A.; Hochkogler, C. M.; Köck, E.; Marchiori, A.; Hans, J.; Widder, S.; Krammer, G.; Sanger, G. J.; Somoza, M. M.; Meyerhof, W.; Somoza, V., Caffeine induces gastric acid secretion via bitter taste signaling in gastric parietal cells. Proceedings of the National Academy of Sciences 2017, 114 (30), E6260.
  9. Rubach, M.; Lang, R.; Skupin, C.; Hofmann, T.; Somoza, V., Activity-Guided Fractionation to Characterize a Coffee Beverage that Effectively Down-Regulates Mechanisms of Gastric Acid Secretion as Compared to Regular Coffee. Journal of Agricultural and Food Chemistry 2010, 58 (7), 4153-4161.
  10. Rubach, M.; Lang, R.; Seebach, E.; Somoza, M. M.; Hofmann, T.; Somoza, V., Multi-parametric approach to identify coffee components that regulate mechanisms of gastric acid secretion. Molecular Nutrition & Food Research 2012, 56 (2), 325-335.
  11. Rubach, M.; Lang, R.; Bytof, G.; Stiebitz, H.; Lantz, I.; Hofmann, T.; Somoza, V., A dark brown roast coffee blend is less effective at stimulating gastric acid secretion in healthy volunteers compared to a medium roast market blend. Molecular Nutrition & Food Research 2014, 58 (6), 1370-1373.
  12. Boekema, P. J.; Samsom, M.; van Berge Henegouwen, G. P.; Smout, A. J., Coffee and gastrointestinal function: facts and fiction. A review. Scandinavian journal of gastroenterology. Supplement 1999, 230, 35-9.
  13. Feldman, M.; Barnett, C., Relationships between the acidity and osmolality of popular beverages and reported postprandial heartburn. Gastroenterology 1995, 108 (1), 125-131.
  14. Brazer, S. R.; Onken, J. E.; Dalton, C. B.; Smith, J. W.; Schiffman, S. S., Effect of different coffees on esophageal acid contact time and symptoms in coffee-sensitive subjects. Physiology & Behavior 1995, 57 (3), 563-567.
  15. Kaltenbach, T.; Crockett, S.; Gerson, L. B., Are lifestyle measures effective in patients with gastroesophageal reflux disease? An evidence-based approach. Archives Of Internal Medicine 2006, 166 (9), 965-971.
  16. Nilsson, M.; Johnsen, R.; Ye, W.; Hveem, K.; Lagergren, J., Lifestyle related risk factors in the aetiology of gastro-oesophageal reflux. Gut 2004, 53 (12), 1730.
  17. Elta, G. H.; Behler, E. M.; Colturi, T. J., Comparison of coffee intake and coffee-induced symptoms in patients with duodenal ulcer, nonulcer dyspepsia, and normal controls. The American Journal Of Gastroenterology 1990, 85 (10), 1339-1342.
  18. Boekema, P. J.; Samsom, M.; Roelofs, J. M. M.; Smout, A. J. P. M., Effect of Coffee on Motor and Sensory Function of Proximal Stomach. Digestive Diseases and Sciences 2001, 46 (5), 945-951.
  19. Buijs, M. M.; Kobaek-Larsen, M.; Kaalby, L.; Baatrup, G., Can coffee or chewing gum decrease transit times in Colon capsule endoscopy? A randomized controlled trial. BMC Gastroenterology 2018, 18 (1), 95-95.
  20. Brown, S. R.; Cann, P. A.; Read, N. W., Effect of coffee on distal colon function. Gut 1990, 31 (4), 450-3.
  21. Douglas, B. R.; Jansen, J. B.; Tham, R. T.; Lamers, C. B., Coffee stimulation of cholecystokinin release and gallbladder contraction in humans. The American Journal Of Clinical Nutrition 1990, 52 (3), 553-556.
  22. Geremew, T.; Abate, D.; Landschoot, S.; Haesaert, G.; Audenaert, K., Occurrence of toxigenic fungi and ochratoxin A in Ethiopian coffee for local consumption. Food Control 2016, 69, 65-73.
  23. Reichert, B.; de Kok, A.; Pizzutti, I. R.; Scholten, J.; Cardoso, C. D.; Spanjer, M., Simultaneous determination of 117 pesticides and 30 mycotoxins in raw coffee, without clean-up, by LC-ESI-MS/MS analysis. Analytica Chimica Acta 2018.


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