Prebiotics - good or bad?

One great thing about this blog is that through interacting with other people, I am learning so much. A commenter had a question about fructo-oligosaccharides - an ingredient she saw in one of her food products - and frankly I really didn't know anything about them. Hence this post! I love it when a question spurs me on to learn more about something - especially as I am relatively new to thinking about nutrition and what we put into our bodies in a more hardcore way. 


What is FOS?
So, what exactly are fructo-oligosaccharides (FOS), and what are they doing in our food and supplements? Let's start with the big word - oligosaccharides are short to medium chains of sugar molecules. Adding fructo to the word indicates that the chain is composed of several fructose molecules. So FOS is really just a bunch of fructose molecules connected to each other chemically. (Similarly, galacto-oligosaccharides are a bunch of galactose - or milk sugar - molecules strung together.)

Inulin, often used as a dietary fiber, is a longer chain of fructose molecules. Sometimes inulin is referred to as an FOS, but FOS are generally shorter chains of fructose, while inulin is a very long chain of fructose. Both FOS and inulin are found naturally in Jerusalem artichoke, burdock, chicory, leeks, onion, aspargus, bananas, wheat, leeks, and tomatoes. FOS can be synthesized by Aspergillus enzmatically acting on sucrose or by the degradation of inulin.

FOS actually behaves quite differently than a solitary fructose molecule. We don't have the right enzymes to digest FOS, so they pass through our stomachs and small intestines intact. The flora in our large intestines and colon, however, are able to feed on FOS. What's more, FOS is preferred by the good bacteria (such as the Bifidobacteria and Lactobacillus strains), though bad bacteria (like Klebsiella, Clostridium, and E. coli) are able to digest it on a limited basis. Because FOS serves as food for friendly bacteria (the kind you find in probiotics), it's considered to be a prebiotic. Get it? Prebiotics feed probiotics.

The Good
There are quite a few health benefits associated with FOS. Have you heard that a happy colon equals a happy body? Well, the health and happiness of your colon and intestines is largely dependent on its bacterial population. The human gastrointestinal tract has a complex ecosystem of hundreds of different types of bacteria. These bacteria have enormously important functions, including protection from infection from foreign bacteria and providing nutrients, including B-vitamins and short chain fatty acids.

The good bacteria in our body feed on FOS with a much greater efficiency than the bad bacteria in our body. In that way, FOS acts as a selective food for the good bacteria. The hope with a prebiotic like FOS is that the good bacteria will get the extra nourishment and thrive at the expense of the bad bacteria, and the bacterial population in your gut will then be mostly good bacteria.

FOS consumption has been associated with a lot of positive results. It's been shown to increase calcium and vitamin K absorption in the colon. It also boosts the bacterial populations' ability to synthesize B vitamins (like riboflaven, niacin, and pyridoxine). The level of short chain fatty acids in the colon is also higher with FOS consumption. All good things for colon health.

Because we can't digest FOS, it serves as a low-calorie dietary fiber, and we all know that we need to be consuming more dietary fiber! FOS is sweet - about half as sweet as table sugar - and is finding popularity as a low calorie sweetener, which is one reason why it's popping up in more and more foods.

The Bad
Of course, everything isn't all sunshine and roses with FOS (and inulin). There are concerns surrounding prebiotics. The biggest concern is that FOS also feeds the bad bacteria. If the microflora in a person's gut is out of balance - with more bad bacteria than good bacteria - this could be especially troubling.

Some people who consume FOS have problems with gas formation, bloating, abdominal pain, and (to a lesser extent) diarrhea. These problems have been attributed in part to actions by bad bacteria. While many people tolerate and are benefited by consumption of FOS, others simply cannot tolerate it and experience intestinal havoc when taking FOS or inulin.

Some claim that FOS and inulin can help those with irritable bowel syndrome (IBS), but clinical studies simply do not support this. Not only does FOS not help alleviate IBS symptoms, some IBS sufferers experience a short term worsening of IBS symptoms when taking FOS or inulin.

What's the bottom line?
FOS consumption has a lot of potentially positive outcomes, but its interactions with bacteria in the gut are still not well understood. Each person's body chemistry is so different, and I suspect that the microflora population (good versus bad bacteria) in a person's colon determines to a large extent how effective - or detrimental - FOS is. For a colon in bacterial balance, FOS and inulin are probably beneficial. For a colon where the bad bacteria have an edge, FOS and inulin might not be such a good thing.

FOS is starting to pop up in a lot of different places. If you buy probiotics (aka good bacteria taken as a supplement), you might see FOS bundled in. Inulin is sold as a dietary fiber (Fiber Choice fiber supplement). And because both are sweet, they're starting to be used as sweeteners in foods too.

In the end, we've decided to be cautious with FOS and inulin. We have irritable bowel syndrome in our family and don't want to risk the detrimental effects that can potentially come along with FOS and inulin consumption. So, for now, we'll stick with natural sources of FOS and avoid FOS as a supplement.

Thanks so much for the question, Rachel! I meant for this post to appear much sooner, but life gets in the way sometimes. Keep those questions coming!