6.4: Stomach

Cells in the stomach lining secrete about 3 quarts of liquid each day. This “gastric juice” includes hydrochloric acid, intrinsic factor, and digestive enzymes that begin the digestion of fat and protein. The fluid is very acid (about pH 2).

Hydrochloric acid is what makes gastric juice so acid. It kills much of the bacteria ingested along with food, and denatures proteins (including enzymes in food).* The acidity also aids mineral absorption, because minerals dissolve more easily in acid fluids. As with other nutrients, minerals must be in solution (dissolved) to be absorbed.†

Intrinsic factor is a protein secreted in the stomach that’s needed to absorb vitamin B₁₂. It attaches to B₁₂, and the combination is absorbed in the lower part of the small intestine. As will be discussed in Chapter 7, some older adults develop a B₁₂ deficiency because of insufficient intrinsic factor. They can get B₁₂ as an injection or from a nasal gel or spray, or take large doses of B₁₂ as a pill.

Alcohol: Very little nutrient absorption occurs in the stomach. But alcohol can be absorbed here, so it can enter the bloodstream that much sooner. It’s a small molecule that’s already “in solution,” and readily absorbed “as is.”

Alcohol only needs to contact the wall of the stomach or small intestine to be absorbed. So you feel its effects the fastest when you drink on an empty stomach—no food to hinder its contact. Also, liquids leave the stomach faster than solids. This speeds alcohol absorption, because the small intestine provides more surface area for absorption.

Eating fatty foods when drinking alcohol helps slow alcohol absorption, because fat stays longer in the stomach. Appetizers served with alcoholic drinks are typically high in fat, e.g., cheese, nuts. Fat slows alcohol absorption by mixing with the alcohol (hindering its contact with the wall of the stomach and small intestine) and slowing its passage from stomach to small intestine.

The stomach lining also has an enzyme that breaks down alcohol. The enzyme lessens the toxic effects of alcohol by breaking some of it down before it’s absorbed into the blood. Women have less of this enzyme than men. As a result, women are more susceptible to alcohol’s toxic effects, e.g., cirrhosis of the liver.

^{*A common misconception is that “natural enzymes in food” aid our bodily functions. But the body treats the enzymes as it does other proteins in food—it digests them and absorbs the resulting amino acids.
†Some brands of mineral tablets (e.g., calcium) don’t dissolve as they should in the stomach. Put a tablet in a half-glass of vinegar at room temperature, and stir vigorously every 5 minutes. If it doesn’t completely dissolve in 30 minutes or less, try another brand.}

Stomach Cancer

Stomach cancer is common throughout the world, but relatively uncommon in the U.S. Stomach cancer has fallen dramatically and steadily in the U.S. for decades (Table 12-1). We now have one of the lowest rates in the world (Figure 12.4).

Long-term infection with the microbe Helicobacter pylori is thought to play a major role in stomach cancer. H. pylori infection is less common in developed countries and in higher socioeconomic groups. H. pylori can also cause stomach ulcers** and gastritis (inflammation of stomach lining), both of which raise the risk of stomach cancer. (H. pylori-caused ulcers and gastritis can usually be cured with a precise regimen of antibiotics and other medication.)

Although much of the world’s population is infected with H. pylori, only a small fraction get ulcers, gastritis, or stomach cancer, presumably because of people’s genetic and environmental differences and different microbial strains.

What’s in our food would be expected to be a strong environmental factor. In fact, stomach cancer rates do seem to reflect the amount of carcinogens (cancer-causing substances) in food. A major source has been foods preserved by salt, smoke, and/or nitrite. Salt isn’t a carcinogen, as such, but excessive amounts can contribute to inflammation of the stomach lining (gastritis), which can increase susceptibility to cancer.

It’s probably not coincidental that stomach cancer rates fell when sanitation improved (lessening H. pylori infections) and the use of home refrigerators and refrigerated trucks became widespread. Fresh fruits and vegetables have become available year-round in most parts of the U.S., and we no longer have to preserve food with salt, smoke, or nitrite. We now eat fewer preserved foods and more fresh fruits and vegetables (thought to protect against cancer). Also, refrigeration retards spoilage (e.g., formation of molds), and some products of spoilage can be carcinogenic.

Stomach cancer likely depends on a combination of risk factors. Carcinogens in food might not cause stomach cancer if the diet was not also high in salt, or the stomach was not infected with H. pylori. As combinations go, note that bacon is very salty, is cured with nitrite, has nitrosamines, and is sometimes smoked. When bacon is then fried, more nitrosamines are formed—and perhaps people who eat a lot of cured meats eat fewer fruits and vegetables. Nitrosamines and other food and nutrition factors will be discussed in Chapter 12.

South Korea and Japan have the highest stomach cancer rates and among the highest salt intakes in the world. Foods preserved with salt (e.g., pickled vegetables, salted fish) and smoked and fermented foods are a traditional part of their diet, whereas fresh fruits and vegetables are not.

Stomach cancer in Korean-Americans and Japanese-Americans has fallen with successive generations (Koreans immigrated here more recently than Japanese.) Stomach cancer is also decreasing in Korea and Japan. Their diet and lifestyle has become more Americanized, and infection with H. pylori has fallen.

Among ethnic groups in the U.S., Korean-Americans have the highest stomach cancer rate. Though lower than in Korea, stomach cancer is caught at a later stage in the U.S. than in Korea. Korea has a national screening program for stomach cancer, as does Japan.

^{**Non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, acetaminophen can also cause ulcers.}