Prebiotics work not only in the gut, but also have been proposed to play an important role in a large range of health benefits from reducing disease risk to possibly curing disease. (As I write this, the words from Stephen Sondheim's "Pirelli's Miracle Elixir" from Sweeney Todd are stuck in my brain.) The claims are long but I will try to put them in large categories.
Prebiotics work on a limited number of gut microorganisms. As a result of prebiotics' ability to change the growth OR the activities of certain gut organisms prebiotics are claimed to do the following:
1. Improve the gut composition which leads to improved gut functions including stool regularity.
2. Improve immune function
3. Decrease the risk of colon cancer
4. Improve mineral absorption
5. Decrease GI infections
6. Decreases obesity, metabolic syndrome and its related problems
This then leads to the myriad of health benefits that are all over the Internet.
I will again look at good studies in humans, explain results that have only occurred in labs, and what is theory. The majority of studies have been done using food ingredients which belong to two groups - inulin-type fructans (ITF) and galacto-oligosaccharides (GOS). These have been shown to stimulate lactobacilli and bifidobacteria, which are good bacteria. To be classified as a prebiotic, it has to be resistant to hydrolysis and GI absorption before the colon, must be fermented by the intestinal micro flora and stimulate the intestinal bacteria associated with health of humans.
IMPROVE GUT COMPOSITION
In a normal gut, things go through the small intestine more quickly compared to the large intestine so there are more bacteria in the large intestine as well as more undigested food. This is where the prebiotics work. The food that we are unable to digest (fiber, complex sugars and proteins) as well lining substances of the gut are fermented by the bacteria and used as their energy source with metabolites left over. These products influence the gut motility.
In only 2 studies were they able to show a positive effect in gut motility with patients that had Irritable Bowel Syndrome. Those patients took 5-7 grams/day of a prebiotic to have an improvement in symptoms. All the other well designed studies showed less good outcomes and they used lower or higher doses.
IMPROVE IMMUNE FUNCTION
There are some very good theories that prebiotics ought to influence the immune system because the gut, through the gut-associated lymphoid tissue (GALT) is significantly involved in both preventing and modifying disease. The problem is that the human GI system is not easily accessible for study. So far the best studies are done in the lab and none have been confirmed with well-designed human studies.
A number of clinical studies are being done in Inflammatory Bowel Disease (IBD). The problems with the studies are many but the ingredients are safe and some of the early results deserve further investigation.
Prebiotics have been added to infant formula to make it more like breast milk, which does improve babies' immunity. The stools do show an increase of bifidobacteria, but whether that translates to improved human health has yet to be proved.
COLON CANCER
The bacteria in your gut manufacture chemicals and some of them can be carcinogens and toxic. Good bacteria produce a low number of carcinogens and bad bacteria produce a large number of toxins by comparison. In theory, if you have good bacteria, you should have less production of toxic waste products in your gut and less risk of cancer. In animals there is a a reduction in colon cancer and in humans, there seems to be a decrease in bio markers in patients at risk for colon cancer who were given symbionics (pre and probiotics.) It has not been proven that there is a decrease risk of cancer in humans, but again, this is a difficult study to do.
MINERAL ABSORPTION
A number of well-designed studies have shown an increase absorption of calcium in prepubertal girls and boys and late post menopausal women. In healthy infants, prebiotics increased iron and magnesium absorption; and in early menopause there is increased copper absorption. In the studies that showed the best mineral absorption, it appears not only is the dose important, but that also using a combination of prebiotics made the mineral absorption more effective.
Whether or not increased absorption leads to improved health has only been proved in lab animals. Although it seems reasonable, the bone metabolism of post-menopausal women is more complex and much of the previous dogma that we have taught women to do (like take high dose calcium) is now being questioned. So far no decrease in the risk of osteoporosis has been shown with prebiotics.
DECREASED GI INFECTIONS
The studies show some effect in rats, and some moderate success in prevention of traveler's diarrhea in humans, but otherwise this has not been as successful as probiotics.
OBESITY AND METABOLIC DISORDERS
Most of the studies on this subject have been done in animals. They have shown a decrease in fat mass, but not a decrease in weight. Also, there is better glucose, lipid, triglyceride, and cholesterol metabolism in the rats. The few human studies available seem to show that prebiotics work by producing a peptide that regulates appetite. But so far whether or not this will actually work in humans has not be shown. What the importance of the actual microbes in the gut are in humans has not been explored because the studies have all sorts of difficulties in trying to devise double blind studies with good placebos
AVAILABILITY OF FOOD
Many regular foods contain prebiotics. These include leeks, onions, Jerusalem artichoke, garlic, asparagus and bananas, to name a few. The quantity of what you have to eat of them to achieve a prebiotic effect differs with the food. Also, the caloric quantity of the food changes which will modify the health benefits of the prebiotic.
SIDE EFFECTS of PREBIOTICS
Prebiotics are fermented in the large intestine, which means gas is produced. The more prebiotics, the more flatulence, cramping and diarrhea. Most people can handle 10-20 grams/meal, but some people complain of side effects with that amount.
So where does that leave us? See my final blog as I try to summarize the health benefits of these topics and try to make sense on what you can do on a daily basis.
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