I was reading about a type of sugar in beans called galactooligosaccharides and came across this, about immunity, in Wikipedia:

Support of Natural Defenses
Human gut microbiota play a key role in the intestinal immune system, in maintaining a disease-free state. The gut and immune system form a complex structure that provides defense against ingested toxins and pathogenic bacteria. A well-balanced gut microflora is thought to play a particularly important role in the natural defense of the human body. Galactooligosaccharides support natural defenses of the human body via the gut microflora,[14] indirectly by increasing a number of good bacteria in the gut and inhibiting the binding or survival of Escherichia coli, Salmonella Typhimurium and Clostridia to the body, reducing the chances of getting infected.[15][16][17][18] Furthermore, GOS can positively influence the immune system—indirectly through the production of antimicrobial substances as the result of galactooligosaccharide fermentation, that can reduce the proliferation of pathogenic bacteria,[19][20] and directly by interaction with immune cells.[21][22][23][24] For example, in infants the usage of GOS has been shown to have a potential role in allergy prevention and reduction of infectious diseases.[25][26] GOS supplementation has also been shown to reduce symptoms of gastrointestinal dysfunction and reduce the number of days with cold or flu in stressed undergraduate students undergoing exams.[27]

Galactooligosaccharides are a type of sugar that humans don’t digest. Specifically, they are short chains of monosaccharides which contain galactose. They pass through our small intestine and arrive in the colon ready for bacteria to consume, like fiber.

There are many types of galactooligosaccharides (which I’ll shorten to GOS). One, common in beans, is stachyose, a 4-sugar molecule containing 2 galactoses, 1 glucose, and 1 fructose. Another is raffinose, a 3-sugar molecule containing 1 each galactose, glucose and fructose. GOS is all over the plant kingdom. Raffinose alone is found in beans, cabbage, Brussels sprouts, broccoli, asparagus, other vegetables, and whole grains.

Humans lack the enzyme to break down GOS, alpha-galactosidase. So GOS in foods end up feeding intestinal bacteria which in turn produces gas (and other beneficial molecules which I’ve discussed). By the way, the product Beano contains our missing enzyme, which is how it works to reduce gas and intestinal discomfort. People who don’t have success with it are probably either not taking enough, or aren’t taking it with the first bite of food. Timing is important.

Most of this I learned in school. The thing that got me started here was how GOS can boost our immunity. I didn’t know that. Look at that one reference, number 27:

Galactooligosaccharide Supplementation Reduces Stress-Induced Gastrointestinal Dysfunction And Days Of Cold Or Flu: A Randomized, Double-Blind, Controlled Trial In Healthy University Students, American Journal of Clinical Nutrition, April 2011

DESIGN: In a randomized, double-blind study, subjects (n = 427) received 0, 2.5, or 5.0 g galactooligosaccharides for 8 wk around the time of fall final exams. Levels of stress and cold or flu symptom intensity (SI; 0 = not experiencing to 3 = severe) were recorded daily. The SI from 9 cold or flu symptoms was summed with 1 d of cold or flu defined as a sum >6. The Gastrointestinal Symptom Response Scale was completed weekly.

RESULTS: Stress was positively related to diarrhea, indigestion, and reflux syndromes and with abdominal pain, average daily cold or flu SI score, and the percentage of days with cold or flu. Gastrointestinal symptom scores for diarrhea (P = 0.0298), constipation (P = 0.0342), abdominal pain (P = 0.0058), and indigestion (P = 0.0003) syndromes were lower after galactooligosaccharide supplementation. The cold or flu SI score was affected by galactooligosaccharides and stress (P < 0.0001); 2.5 g was associated with a lower SI score across all levels of stress, but 5.0 g was protective only at lower levels of stress. The percentage of days with cold or flu was associated with galactooligosaccharides within different body mass index categories (P = 0.0002), wherein a 40% reduction in the percentage of days with cold or flu was observed in normal-weight individuals with 5.0 g galactooligosaccharides. This effect was not observed in overweight or obese individuals.

CONCLUSIONS:Acute psychological stress was directly related to symptoms of gastrointestinal dysfunction and cold or flu. Galactooligosaccharide supplementation reduced these symptoms and the number of days with cold or flu.

So, consuming GOS, by supplement or perhaps by the foods that contain it … beans, broccoli, cabbage, corn, wheat, peppers, everything on the label of a Beano box … might reduce length and severity of flu. The mechanism isn’t something I understand well:

Recently, the concept of the brain-gut-enteric microbiota axis was introduced, which suggests bidirectional communication between the gastrointestinal tract and brain with input from the enteric microbiota (10). Another model in which cortisol may be driving changes in immune function and enteric microbiota is that of immunosenescence (11). Vulevic et al (12) supplemented the diets of older adults with a prebiotic, galactooligosaccharides, and observed increased numbers of beneficial bacteria (ie, bifidobacteria), decreased production of IL-6, and increased natural killer cell activity.

The foods we eat create a unique population of microorganisms in our gut, our “microbiota,” that contributes to communication between our brain and gut. Right? In turn, boosting immunity. Look at the last line in the quote above … GOS “increased natural killer cell activity.” I’ve a lot of reading to do.

Something else:

The dose of 2.5-g galactooligosaccharides was more effective than the 5.0-g dose at reducing symptoms associated with abdominal pain (ie, abdominal pain, hunger pains, and nausea) and indigestion syndrome (ie, rumbling, bloating, burping, and gas). This is of interest to note considering that galactooligosaccharides are fermented by the intestinal microbiota, which results in gas production (17). The higher dose of galactooligosaccharides (5.0 g) yielded a lower indigestion syndrome score than did the placebo (0 g) (Table 2). Although 2.5 g galactooligosaccharides was associated with slightly improved stool consistency, 5.0 g galactooligosaccharides was associated with the decreased likelihood of constipation syndrome.

The very foods that people avoid because they think they give them indigestion, could actually result in less indigestion (ie, rumbling, bloating, burping, and gas), and less diarrhea, constipation, and abdominal pain. I know, I’m not quite on that page either. But recall the study where people’s IBS (irritable bowel syndrome) went away when they took a placebo, and they knew it was a placebo!

Oh, and … if it’s true that GOS improves immunity then taking Beano might lessen the benefit since Beano metabolizes GOS before it gets to the colon. No food for bacteria to eat.

The moral of the story: Eat beans, and the other foods in this photo, to feed colonic bacteria and boost immunity.