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You are a symbiotic organism. Millions of tiny organisms inhabit your digestive tract and live merrily in a symbiotic relationship with you. You provide them a place to live that is hospitable (proper pH, temperature, etc…) as well as a constant food supply. In return, these little microorganisms provide valuable services like converting indigestible calories into digestible ones.

What is even more fascinating is that we have evolved to live in symbiosis with these creatures on such an intimate scale. The microflora that inhabit your gut relay information to your body that manipulates all sorts of things, from your immune system to your metabolism. It makes you wonder who’s in charge. Maybe we are just walking, talking, transport vehicles for these little bacteria…

Since the microflora that inhabit your digestive system can influence so many things, it behooves us to ask the question: “How might the micro organisms that inhabit my digestive tract impact my body composition?” That is the question I intend to answer in this article.

Speaking the Language

To properly discuss how digestive health plays a role in one’s body composition, we have to get some terminology squared away. Like all advanced subjects, this area has its own jargon. The following three terms are used extensively in the literature and it is important to understand them before we continue.

1. Pre-Biotic: A pre-biotic is a nutritional substance that brings about the growth of the bacteria and organisms that inhabit your digestive system. Compounds such as inulin and fructo-oligosaccharides (FOS) are collectively known as fructans. They are non-digestible strings of fructose molecules that are classified according to their length. In general, inulin (which comes from chicory root) is considered a long chain whereas FOS, which are generally synthetically derived through fermentation, are considered short chain. Each is non-digestible by humans, but the bacteria that inhabit your gut thrive off of them. By ingesting these compounds the bacteria grow like crazy—particularly the colonies in the colon and lower intestine.2. Pro-Biotic: A pro-biotic supplement is probably what you normally think of in this category. It is a supplement that is composed of lots of bacteria. Often they are marketed as a means of replacing lost microflora due to antibiotic use or excessive alcohol consumption. They primarily affect the microflora make up of the upper intestine.3. Synbiotic (not symbiotic): Synbiotic supplements are a combination of both pre-biotics and pro-biotics. They contain the bacteria themselves and a food source that promotes colony expansion.

Microflora and Body Composition

So the question at hand is why should you give a rat’s ass about any of this—especially if you don’t normally have digestive tract problems? The answer is a simple one. It could improve your health as well as your body composition!!! Your digestive tract plays a very large role in not just your overall health but your body composition as well. There are several ways in which the gut contributes to your appearance.

The first way that I would like to discuss is direct neuronal signaling. There are nerves that run from the stomach directly to the brain. Specifically, they run to the adrenal medulla area. I wrote rather extensively about these nerves in my M&M

leptin series, so I will simply refer you there for further reading. The short-and-sweet version is that these nerves sense mechanical stretch and relay that information to your brain. In other words the nerves say “hey brain there is some food in here – no need to make the poor guy hungry anymore.” Since I have already written extensively on this subject before I will move on so that we can spend more time on the other ways your digestive system modulates your metabolism.

The secreting of various proteins is the next mechanism of action. Really this is many individual mechanisms but I will group them all together for the purpose of this article. The gut releases ghrelin, peptide YY (PYY), GIP-1, GLP-1, and cholecystokinin (CCK) all of which play an important part in modulating your metabolism.

Unless you have been living under a rock I am sure you have heard about ghrelin and CCK before. Ghrelin is a protein released by your digestive tract when it’s empty. Ghrelin then wanders up to the brain where it increases appetite. It also does some other interesting things but this is not an article about ghrelin so I will just move on. CCK and PYY are released when the digestive tract senses food. CCK is kind of the anti neuropeptide-Y (another peptide that makes you hungry and suppresses metabolism, thyroid, androgens etc…). I covered NPY very extensively in my leptin articles so again I will refer you to that series. I have not however talked much about PYY, so let’s now turn in that direction.

There is an area of the brain called the Arcuate nucleus (ARC). The arcuate nucleus controls the production of MSH and CART. The MSH that is produced in the ARC acts on the lateral hypothalamus (LH) to decrease NPY production. When NPY goes up, metabolism goes down and catabolism increases. When NPY goes down, metabolism and anabolism go up. This is because NPY acts as a switch regulating whether the body favors thyroid production or cortisol production. NPY is in my opinion the switch that acts to determine the metabolic and anabolic/catabolic state of the body. So it is wise to trace all of the pathways back to NPY production and see how it is affected.

In the ARC there are neurons that have ghrelin receptors. When ghrelin activates these receptors, the receptors decrease MSH production, thus slowing metabolism and putting the body in a state of catabolism. This is to be expected. After all, the gut is telling the brain “hey there is no food in here!!” So the brain responds accordingly by increasing appetite and producing a net catabolic state.

Interestingly enough, these exact same neurons that have ghrelin receptors also have PYY receptors. As expected, the two are in opposition. When PYY binds to these receptors it increases MSH production, thus having the opposite effect: it increases metabolism and places the body in an anabolic environment. So for all meaningful intents and purposes, PYY is the anti-ghrelin. The two are in a constant battle to determine the state of MSH production in the ARC.

Glucagon-like peptide-1 (GLP-1) and Gastric inhibitory polypeptide/glucose-dependent insulinotropic polypeptide (GIP-1) are two peptides produced by the gut that help control glucose disposal and insulin sensitivity/secretion. They are both known as incretin hormones and it is your author’s opinion that they play an extremely important and fascinating role in human physiology. Sadly, to cover both peptides adequately would take an inordinate amount of time and will have to wait for a future article. Suffice it to say these two little buggers are extremely important in determining insulin sensitivity, and they play crucial roles in diabetes, syndrome X and obesity.

Finally, the gut can also alter body composition through the production of short chain fatty acids (SCFA). SCFA are fatty acids that have extremely short hydrocarbon chains. Believe it or not, things like acetic acid (vinegar), citric acid (lemon juice), and carbonic acid (soda pop) are all short chain fatty acids. SCFA can have profound affects on your body’s metabolism. Hell, I could and probably should devote an entire article to vinegar, as I feel it is probably the most underused/underrated supplement out there.

Anyway, the helpful little bacteria that inhabit your digestive system digest some of the compounds in the food you eat and produce short chain fatty acids as a waste product. These SCFA are then absorbed and can manipulate your metabolism (among other things). Butyrate is one such fatty acid, for example, that is produced by the microflora of your gut and acts as a PPAR-alpha agonist just like fish oil, SesaThin and the fibrate drugs. Suffice it to say these SCFA can have profound effects.

The Results

All that low level science mojo is all well and good but what exactly will taking digestive supplements do for you? Quite a lot actually—especially when you consider the cost. I think the pre-biotic supplements offer some of the best bang for the buck out there because they are so incredibly cheap.

The pre-biotic supplements like inulin and FOS are well studied for their ability to lower plasma lipids and improve cholesterol profiles. If you recall form my write up on PhenoGen, I believe that by lowering plasma triglycerides one can increase his/her leptin and insulin sensitivity and thus improve his/her body composition.

This lipid-lowering effect is most often attributed to the SCFA mechanism of action. Specifically, it is attributed to butyrate and acetate production. It is thought that acetate creates a futile cycling of carbohydrates from glycogen to glucose-6-phosphate (G6P) and back again in the liver. This wastes calories. As mentioned, butyrate is a PPAR-alpha agonist that promotes the utilization of fatty acids for fuel and lowers plasma triglycerides.

Sadly, much of the research on butyrate and acetate is performed on rats; the data in humans is somewhat mixed. This is because butyrate and other SCFA profoundly affect the lipogenic pathways. These pathways contribute extensively to plasma lipids in animals but are mostly inactive in humans, so we should expect that human results would not be as stunning. In rats, treatment with fructans such as inulin or FOS reduce fat pad weight, lowers plasma triglycerides, improves cholesterol profiles, protects against diabetes and fatty liver in fructose-fed rats, and protects against endotoxic shock induced by Lipo-polysaccharide (LPS) administration.

Another reason the human data is hit-or-miss is that gastrointestinal side effects start to appear when individuals hit the 15g/day marker of FOS. This basically means the subjects get very bad gas. On the other hand, doses of 10g/day are well tolerated and show statistically significant effects in most of the studies. In normal individuals 10g/day primarily results in a lowering of serum lipids with a noticeable but not statistically significant reduction in LDL (bad) cholesterol. In people who already have elevated plasma lipids, this dose of FOS results in a small but not statistically significant reduction in plasma lipids but a statistically significant drop in LDL (bad) and increase in (HDL) good cholesterol.

So, in normal individuals 10g/day results in reductions in serum lipids, and in individuals with elevated serum lipids 10g/day results in an improved cholesterol profile. Not that exciting, right? Still it’s a nice benefit. Luckily, there is more to FOS than a simple reduction in plasma lipids and an improved cholesterol profile.

A recent study in rats showed some amazing results. The authors hypothesized that pre-biotics like inulin and FOS are able to alter the secretion patterns of some of those proteins we talked about earlier. The researchers fed normal Wistar rats either a normal diet or one enriched with 100g of fructans. They tested long chain inulin and short chain FOS separately to see if chain length had any effect.

The first thing the researchers found was that any of the groups that received the fructans ingested fewer calories and showed decreases in fat mass as a result. More interestingly, they found that the animals that received FOS in their diet had a higher concentration of GLP-1 in the portal vein. It gets even better. The researchers also tested what would happen to these rats when they fasted for 8 hours. In the rats fed FOS, ghrelin levels were significantly lower than control animals. Normally an 8 hour fast would send ghrelin levels though the roof, but the animals that received the FOS were protected from this.

In another study the authors focused on the contribution of GLP-1 and GIP-1 to the equation. Again, they took normal healthy Wistar rats and fed them normal chow or chow supplemented with 10% FOS. The researchers found that the animals that received FOS had lower fasting plasma insulin levels, better sensitivity to the oral glucose tolerance test, and reduced insulin production during the oral glucose tolerance test.

Best of all, this all happened without inducing hypoglycemia. In fact, the animals that received FOS showed normal levels of plasma glucose even though they had significantly reduced levels of plasma insulin. The rats received all the benefits of normal blood glucose levels that I discussed in my leptin articles while still lowering plasma insulin concentrations (presumably, humans would see similar results).

Still, there is much to be learned. Unfortunately we still don’t know all that much about the microflora makeup of the gut, so we cannot make a reasoned attempt at analysis as to why these changes manifest themselves. We know that pre-biotics and synbiotics bring about these favorable changes.

Additionally, we know that they alter the balance of certain bacteria, favoring one over another. But we don’t know the specifics. This is because many of the bacteria and microorganisms that inhabit our digestive tracts can’t be raised in culture. In other words, scientists can’t grow them in a dish to study them, so we are still in the dark as to how the pre-biotics and the microflora alter these protein secretions.

Hopefully, in the future, better techniques will be developed that will allow us to understand the mechanism behind these favorable alterations.

Health Benefits

Besides improving markers that could positively affect body composition, the fructan based pre-biotics also have several other health benefits.

The first such benefit is improved mineral absorption, which has been well studied in both lab animals and humans. FOS and other pre-biotics can dramatically increase the absorption of Calcium, Magnesium and Zinc.

Fructans have also been studied in animals and humans for their ability to bolster the immune system. The effect is quite profound. In fact, this immune system boost is attributed to the rats improved protection from endotoxic shock that I discussed previously. That mechanism was identified to increase hepatic macrophage content. Macrophages are the killer cells of the immune system—they undergo phygocytosis and eradicate harmful bacteria.

Synbiotics can also correct alterations of the gut’s pH. For example, several case reports have successfully treated candida infections with anti-fungal agents and synbiotics. Frankly I think the whole candida thing is quite over blown. If you search for these little bacteria on the web you will get a host of quacks talking about how everyone on earth is infected. I feel I would be remiss if I did not at least mention it even though I feel it’s hardly an issue for concern.

In some individuals, the pH of the intestine or colon can change due to medical treatment or some other condition. When this happens the candida bacteria converts into a yeast fungus. This fungus grows and can even rupture the intestine. Synbiotics and anti-fungals are normally used to treat this and other similar conditions. The anti-fungal kills the candida fungus while the synbiotics help restore the digestive system’s proper pH so that the problem will not reappear.

Bottom line: if you are concerned about maintaining proper pH of your digestive system, Synbiotics can help. They have also been used to treat similar conditions like thrush or recurrent yeast infections, even if these issues are a bit over blown.


Now the fun part. If this stuff is so great, why don’t you hear about it all the time? Probably money. There is no money to be made on it, mostly because the stuff is so incredibly cheap. In fact that’s one of the reasons I decided to write this article. People email me all the time asking for an opinion on one product or another—generally some fifty dollar snake oil. Why, people, why?!? Yet if I mention FOS I am met with blank stares.

Sure, FOS is not the end-all be-all. It’s not going to get you ripped and hyooooge overnight. But it is healthy, can improve your body composition, and is dirt cheap. And when I say cheap, I mean cheap. If you shop around you can generally find a kilo of FOS for about $10-15. Even at high dosages we are talking about twenty five cents per day and only a nickel a day at lower doses. That’s like “creatine” cheap. Because of its low cost and its health benefits I consider it a required staple along with fish oil, and a multi-vitamin/mineral product.

For recommended dosages, it varies. Most studies show desired results with 10/g per day, but studies using far less have shown results as well. Even as little as 1g/day would be worthwhile depending on how much fructan you get in your normal daily diet. As stated previously, side effects start to appear at the 15g/day marker.

I have personally found that those side effects never appear even at much higher dosages so long as the dosage is increased slowly. I started with 1g/day and gradually increased my dose all the way up to 30g/day over the course of 6 months and experienced no gastrointestinal problems (gas). This might be due to the fact that I have used FOS and not inulin. I have not seen an analysis of this subject, but it appears that inulin is not as well tolerated as FOS.

The pro-biotic/synbiotic side of things is a little more complicated. Personally, I recommend that you just eat some yogurt. Part of the reason for this is that pro-biotics are generally quite expensive. Also, you can’t be sure of the actual content. If the bottle has been sitting on the shelf for quite some time it’s quite possible that the majority of those bacteria you have just paid hard earned money for are dead and gone. So I say opt for yogurt.

Personally, I eat a serving of yogurt three times per weak and ingest 15g of FOS per day as part of my standard diet and supplement regimen. So if you want a specific plan you can build off of that. As stated, I would start your FOS usage at no higher than 1g/day initially unless you want some pretty intense gas.

In conclusion, I hope that I have convinced you that this is a good product. There are lots of excellent products that can produce meaningful results and do it on the cheap. In the future I plan to address several other products like this that I think have fallen under the radar. Products like FOS, vinegar, fiber, vanadium, and baking soda are all quite effective and backed by some real science. Sadly, you never hear about them because there is just no money to be made selling them. So I hope to make this but the first of many articles in a series that covers these forgotten gems of fitness.

Questions or Comments? CLICK HERE to pose your questions and receive live feedback from Spook, as well as the Mind and Muscle staff and fellow readers!


1. Prebiotic carbohydrates modify the mucosa associated microflora of the human large bowel. Langlands SJ, Hopkins MJ, Coleman N, Cummings JH. Gut. 2004 Nov;53(11):1610-6.

2. Inulin-type fructans modulate gastrointestinal peptides involved in appetite regulation (glucagon-like peptide-1 and ghrelin) in rats. Cani PD, Dewever C, Delzenne NM. Br J Nutr. 2004 Sep;92(3):521-6.

3. Kupffer cell activity is involved in the hepatoprotective effect of dietary oligofructose in rats with endotoxic shock. Neyrinck AM, Alexiou H, Delzenne NM. J Nutr. 2004 May;134(5):1124-9.

4. Citrus pectin and oligofructose improve folate status and lower serum total homocysteine in rats. Thoma C, Green TJ, Ferguson LR. Int J Vitam Nutr Res. 2003 Nov;73(6):403-9.

5. Prebiotic inulin enriched with oligofructose in combination with the probiotics Lactobacillus rhamnosus and Bifidobacterium lactis modulates intestinal immune functions in rats. Roller M, Rechkemmer G, Watzl B. J Nutr. 2004 Jan;134(1):153-6.

6. Oligofructose protects against the hypertriglyceridemic and pro-oxidative effects of a high fructose diet in rats. Busserolles J, Gueux E, Rock E, Demigne C, Mazur A, Rayssiguier Y. J Nutr. 2003 Jun;133(6):1903-8.

7. Applications of inulin and oligofructose in health and nutrition. Kaur N, Gupta AK. J Biosci. 2002 Dec;27(7):703-14.

8. Effects of consumption of probiotics and prebiotics on serum lipid levels in humans. Pereira DI, Gibson GR. Crit Rev Biochem Mol Biol. 2002;37(4):259-81.

9. Long-term consumption of fermented dairy products over 6 months increases HDL cholesterol. Kiessling G, Schneider J, Jahreis G. Eur J Clin Nutr. 2002 Sep;56(9):843-9.

10. Inulin and oligofructose: effects on lipid metabolism from human studies. Williams CM, Jackson KG. Br J Nutr. 2002 May

11.Insulin, glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide and insulin-like growth factor I as putative mediators

of the hypolipidemic effect of oligofructose in rats. Kok NN, Morgan LM, Williams CM, Roberfroid MB, Thissen JP, Delzenne NM. J Nutr. 1998 Jul;128(7):1099-103.

12.Oxyntomodulin and glucagon-like peptide-1 differentially regulate murine food intake and energy expenditure. Baggio LL, Huang Q, Brown TJ, Drucker DJ. Gastroenterology. 2004 Aug;127(2):546-58.

13. Peptide YY directly inhibits ghrelin-activated neurons of the arcuate nucleus and reverses fasting-induced c-Fos expression. Riediger T, Bothe C, Becskei C, Lutz TA. Neuroendocrinology. 2004;79(6):317-26.

The Gut and the Body

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