Carbohydrate Malabsorption – A Root Cause

Sometimes the medical world and the internet meme world converge. One example of that is how certain diagnoses can go in and out of style. The one I’m going to talk about today is one I think should not go out of style, one that I think is far more prevalent than people think. That is “Carbohydrate Malabsorption”. Something you don’t hear much about from either the medical world or the internet meme world. But this may very well be the number one cause of gut issues, a major contributing cause, or a result of gut problems. 

Looking back at the research I can find studies mentioning “carbohydrate malabsorption”, “sugar intolerance”  and “intestinal sugar malabsorption” dating back to the 1960s. With the use of “respiratory hydrogen (H2) excretion” dating back to at least 1970.  These are not new concepts.

Today everyone likes to talk about SIBO (small intestinal bacterial overgrowth) as being the root cause of nearly all gut maladies. I’m here to tell you, it is not. SIBO can often be a symptom, but it isn’t what started everything. But it is part of a chain of events that can cause issues such as leaky gut, SIBO diarrhea, SIBO constipation, nutrient malabsorption, and even anxiety.  It was only a few years ago that most doctors (including gastroenterologists) didn’t even know what SIBO was; most thought that the small intestine was sterile. Of course now that they have prescriptions they can write for it (e.g. Xifaxan and Linzess) doctors are diagnosing SIBO right and left.

In a way all of this attention to SIBO is a good thing, doctors have learned more about how the gastrointestinal tract works and they don’t laugh at their patients that bring it up. I actually had that happen once; then he said, “where did you learn that? On the internet? The only time the small intestine has bacteria in it is if you have food poisoning”.  But there are two problems with all of this attention to SIBO; 1) they forget that the colon is probably also out of balance (and sometimes the small intestine isn’t involved at all. 2) They are missing the root cause. (today I got a message from a woman who said in part “I have SIBO that the doctors diagnosed me with without doing any testing”. Of course they wanted to write her a prescription)

I have people ask me about the “root cause” nearly every day. The patients understand that it is important, even if most doctors don’t (actually they understand, but when doctors don’t know something, or don’t have a prescription for it, they tend to ignore it. Hoping you’ll stop talking about it before they have to say the words they hate the most, “I don’t know”).  Now admittedly the “root cause” is like finding the smallest unit of matter. We used to think that was a molecule, then an atom, then protons and neutrons, now I think it is a “quark”.  But who knows if that is truly the smallest. The same thing for “the root cause” of gut issues.  Nevertheless, it is very helpful to trace back a problem as close to the root as possible.

So let’s look at SIBO. SIBO means we have an overgrowth of unwanted bacteria in the small intestine. Usually this bacteria is “colonic” in nature (belongs in the colon of some mammal) and creates toxins and/or noxious gas. An overgrowth of beneficial bacteria is possible, but doesn’t happen very often; when it does happen the symptoms are very mild and the body usually knows just how to deal with it (with rare exceptions). The fact that beneficial bacteria don’t cause many symptoms is why they are defined as PRO BIOTIC (good for health), they can not be considered probiotic and create toxins. But how did we get an overgrowth of this bacteria?  We know that SIBO is causing us symptoms, but what is the “root cause” of SIBO?

There is no one answer to this last question as there is no one cause of SIBO. Here are a few of the “root” causes of SIBO.

• Abdominal surgery, Diverticulosis, radiation treatment, bypass surgery (Roux-en-Y)
• Antibiotics – as they can destroy the microbiome, leaving it vulnerable 
• Other Medications – especially antacids, narcotics, and antispasmodics 
• Diabetes – may be because it leads to carbohydrate malabsorption
• Celiac Disease
• Food poisoning – which can also destroy the microbiome
• Organ dysfunction (such as pancreatitis, gallbladder, kidney) – SIBO bacteria may also damage these organs.
• Slow Motility – Any number of causes, including nearly everything else listed here
• Over consumption of strong probiotics
• Carbohydrate malabsorption – primary or a comorbidity

The last two may be the only one you have control over. Even though carbohydrate malabsorption isn’t talked about very much, it may actually be one of the most common causes of SIBO. To make things even more confusing carbohydrate malabsorption may be caused by one of the other causes in the list; for example, pancreatitis will affect the enzymes that break down certain sugars (such as lactose and sucrose). Carbohydrate malabsorption can be the root cause or SIBO or a comorbidity, meaning that something else is causing SIBO but carbohydrate malabsorption is contributing. You can also have carbohydrate malabsorption and not experience any symptoms as there is no bacterial overgrowth (yet). 

Tracing things further towards the “root”; Carbohydrate Malabsorption can have several causes as well. Some are the same as for SIBO.

• Idiopathic – The etiology (cause) is not known
• Enzyme deficiency – enzymes created in the small intestine to break down sugars are not being made. Can be genetic (e.g. often the case with lactose) or from damage to the brush-border cells.
• Damage to brush-border cells can be caused by surgery, SIBO, food poisoning, celiac disease, etc.

Carbohydrate malabsorption may actually be quite common, but in many cases may not cause noticeable symptoms (however, this can change at any time). In fact studies have shown that even healthy children can malabsorb apple juice, 65% of the children tested (through a hydrogen breath test) showed malabsorption (with an average 43ppm of hydrogen peak, over twice that required for a SIBO diagnosis).

“Apple juice malabsorption, as judged by a peak breath H2 excretion of > or = 20 ppm, was found in 11 children (65%) and 4 adults (33%)… Fructose, and not sorbitol, is the sugar responsible for the increase in breath H2 after apple juice consumption and therefore for the diarrhea accompanying excessive apple juice consumption in toddlers.” — PubMed ID#8433238

In the following study they showed that the malabsorption of molasses (which contains sucrose, glucose, and fructose) led to the production of hydrogen, methane and hydrogen sulfide (H2S) gasses. 

“The incomplete absorption of carbohydrates may cause serious problems for the affected patients, and is a frequent cause of so-called non-specific abdominal complaints… These complaints are a major problem throughout the world, with up to 30% of the population in Western countries being affected…  There is a wide range of symptoms; the predominant ones are pain, flatulence, constipation and diarrhea… The most important carbohydrates that routinely cause clinical abdominal complaints are lactose, fructose, and the sugar alcohol sorbitol… the mechanisms of carbohydrate absorption are still not completely understood” — PubMed ID#PMC4171253

The prevalence of lactose intolerance varies from region to region, most Asian and Africans are lactose intolerant, with rates varying considerably among other populations. People may also develop intolerance later in life. 

Carbohydrate malabsorption can cause SIBO, and SIBO can also cause carbohydrate malabsorption. 

“Small intestinal bacterial overgrowth (SIBO) leads to carbohydrate malabsorption” — PubMed ID#PMC7209350

“Sugar malabsorption in the bowel can lead to bloating, cramps, diarrhea and other symptoms of IBS as well as affecting absorption of other nutrients.” — PubMed ID#PMC4069289 

“SIBO has been considered a secondary condition that develops… with poor nutritional outcomes, including… carbohydrate malabsorption” — PubMed ID#PMC4725020 

The 3 most common sources of carbohydrate malabsorption are; lactose intolerance, fructose malabsorption,  and sugar alcohols (such as mannitol, sorbitol, maltitol, isomalt, lactitol, and xylitol). 

Fructose Malabsorption

Fructose malabsorption has not been well studied until recent years. They’re finding that up to 70% of people are fructose intolerant when given 50 grams of fructose (50 grams is the amount of lactose used in a lactose tolerance test). Some people will malabsorb fructose after only a gram or two! Whether they suffer symptoms can depend on the bacterial composition in their gut.

Sorbitol (and most other sugar alcohols) are malabsorbed by almost everyone. Even at 10 gram challenges malabsorption rates often show 100% of the people will malabsorb it. Again, whether they have symptoms or not depends on their balance of gut bacteria.

When you malabsorb one of these sugars it causes an increased “osmotic load” (more water is pulled into the small intestine). This can then cause the contents of the small intestine to rapidly get dumped into the colon (depending on how much your consumed and malabsorbed), ultimately leading to bloating and diarrhea. Having all of this malabsorbed sugar (and other food that was consumed with it) dumped into the colon leads to a dysbiosis of bacteria in the gut. Beneficial bacteria consume foods that we normally do not digest / absorb, such as fiber and resistant polysaccharides (complex sugars that we can break down and utilize); bad bacteria thrive on sugars and undigested foods. The colon should never see simple sugars and other than trace amounts of sugar alcohol.  

Sugars in liquid form are even worse. This sugar can pass through the small intestine very quickly, not giving it enough time to be absorbed. Parents have been told for many years that apple juice is healthy for their children, as the study above shows, it is not. Much of the sucrose (table sugar) and fructose will be malabsorbed, changing the microbial composition in the child’s gut. Most children will have no obvious symptoms, but over time this imbalance of bacteria will lead to healthy issues. Often this leads to gut symptoms in their teens and twenties (if not sooner). Of course this issue is not limited to apple juice, any sugary juice or soda will also cause problems.

“Carbohydrate malabsorption is frequent in patients with functional gastrointestinal disorders and in healthy volunteers and can cause gastrointestinal symptoms mimicking irritable bowel syndrome (IBS)… Of the 2,390 patients with IBS-like symptoms, 848 (35%) were symptomatic lactose malabsorbers and 1,531 (64%) symptomatic fructose malabsorbers. A combined symptomatic carbohydrate malabsorption was found in 587 (25%) patients… fructose and lactose that remain in the lumen of the small intestine subsequently reach the colon and are fermented by resident bacteria.5–7 Degradation products of the bacterial metabolism are hydrogen (H2), carbon dioxide, hydrogen sulfide, methane” — PubMed ID#PMC4015196

“of those who had carbohydrate malabsorption on an oral glucose tolerance test, 75% were diagnosed with SIBO” — PubMed ID#PMC3099351 

Though I would expect to find a large number of people with IBS that have fructose malabsorption, this study also found that 20% of the control group also had it! 

“Fructose malabsorption (FM) mimics symptoms of irritable bowel syndrome (IBS)… The 15-g fructose HBT yielded positive results in 7 of the 35 (20.0%) patients with IBS… The 25-g fructose HBT was positive in 16 of the 35 (45.7%) patients with IBS and in 8 of the 35 (22.9%) controls” — PubMed ID#PMC5885730 

I receive a lot of negative feedback whenever I advise people to avoid fructose; after all, “fruit is good for us”. The fruit of our ancestors was good for us, it was high in soluble fiber and vitamins, but very low in sugar. Today fruit has been selectively bred to be much higher in sugar, and, because fructose tastes sweeter than sucrose, very high in fructose. We also have the advantage today of being able to eat this high sugar fruit 365 days per year; our ancestors only had fruit in season. They also expended a lot of energy gathering this fruit, a process that had to be done every few days as there was no refrigeration. 

My advice would be that anyone with IBS/SIBO symptoms (including IBS/SIBO-C) should limit their fruit consumption to low sugar fruits and berries. Try to consume no more than 10 grams of fructose per day, never in liquid form (no fruit juicing). Because table sugar is 50% fructose (bound to glucose) it too will need to be limited (see The Gut Health Protocol for sugar/carbohydrate limitations). If you are symptom free and have no IBS/SIBO you can consume more fruit, however, I still advise that this be low sugar/low fructose. Try to limit fructose consumption to less than 50 grams per day (again, never in liquid form. Dried fruit usually contains far more fructose than fresh).

Fructose Content of Fruits

Dates (32g)
Raisins (30g)
Figs (dried) (23g)
Apricots (dried) (12.5g)
Prunes (12.5g)
Jackfruit (9g)
Grapes (8g)
Pears (6.5g)
Apples (6g)
Persimmons (5.5g)
Cherries (5g)
Bananas (5g)
Mangos (5g)

Lime juice (0.6g) 
Lemons (1g)
Cranberries (0.6g)
Apricots (fresh) (1g)
Nectarines (1.4g)
Peaches (1.5g)
Clementines (1.6g)
Grapefruit (1.8g)
Cantaloupe, Honeydew Melon (2-3g)
Pineapple (2g)
Oranges (navel) (2.3g)
Raspberries, Blackberries, Strawberries (2.4g)
Plums (3.1g)

Personally I avoid foods in the left column with the exception of an occasional half a banana or a cherry or two. 

Someone with true fructose malabsorption will probably also need to avoid foods high in “fructans” and other sources of fructose.  These include honey, high fructose corn syrup, onions, and garlic. There is a long list in Appendix Q of The Gut Health Protocol. You can also find a graph of foods to avoid at this link. 

Lactose

Most adults have some level of fructose malabsorption, though they may not have symptoms and may not even produce hydrogen when consuming it. However, they may eventually develop symptoms as lactose (milk sugar) does not belong in the colon and it readily feeds bad bacteria. Luckily you do not need to avoid all dairy to avoid lactose. Hard (aged) cheeses and homemade kefir have had the lactose consumed during fermentation. Soft cheeses will still have enough lactose to cause trouble. Homemade kefir can be lactose free if fermented for 48 hours or longer.

In the following study they found that even 91% of healthy controls have lactose intolerance, yet half of those had no symptoms. (CFD=chronic functional diarrhoea)

“Lactose malabsorption was present in 27/31 (87%) patients with CFD and 29/32 (91%) healthy controls (P = 0.708). From the patient group 14/27 (52%) had lactose intolerance and 13/27 (48%) experienced no symptoms (lactose malabsorption controls).” — PubMed ID#20132150 

For people with symptoms the most frequent is diarrhea. But any carbohydrate malabsorption can eventually lead to SIBO and severe dysbiosis. Adult humans simply are not designed to consume dairy. I think we can probably fool mother nature most of the time, but that leaves us with some risk. Consuming lactose containing dairy with a lactase enzyme supplement can help reduce this risk.

Other Carbohydrates

There are other carbohydrates that can be malabsorbed as well. Plain table sugar (sucrose) can be malabsorbed, though not overly common, it isn’t rare either. In fact, as shown in a study above, liquid forms of sugar can easily malabsorp. If you have to consume sugar it is best that it is cooked into a food that contains fat, protein, and more complex carbs. It is also best to consume sugars as a dessert, after a meal. This helps slow transit, allowing the digestive system to do its job better. Remember, that is you absorb the sugar, the bad bacteria can not.

Sugar alcohols aren’t exactly carbohydrates, but function that way to microbes. Nearly all sugar alcohols are malabsorbed to some degree. Again, these include mannitol, sorbitol, maltitol, isomalt, lactitol, and xylitol (note the “itol” and the end of most of these). Erythritol is a sugar alcohol but it is easily absorbed by the small intestine; therefore it causes the fewest problems. Some studies show that Erythritol can increase fructose malabsorption.

The sugar Glucose / Dextrose probably malabsorbs the least of the simple sugars as our bodies utilize glucose very effectively. However, within the first 2-4 feet of the small intestine bad bacteria can still get to it prior to its absorption. If you have SIBO you would still need to be careful when consuming glucose.

Maltodextrin – this is often used by bodybuilders and athletes, it is also found in some elimination diet formulas. However, there are several studies showing that it can cause inflammation in the gut and perhaps lead to Crohn’s Disease. Although it absorbs quickly, you are better off using dextrose.

More complex carbohydrates (such as starches in potatoes and rice) can also malabsorb, but this is usually due to a lack of sufficient digestive enzymes. This can often be rectified by taking a digestive enzyme supplement. 

My Advice

Especially during the kill phase I would avoid all sugars, including those naturally occurring in fruit and dairy. Then after the kill phase is over slowly add back small portions of sugar containing foods and watch closely for any symptoms (bloating, gas, stomach distress, etc.)  Because these symptoms may not start until the sugar passes through the colon, symptoms may not start for 8-36 hours, depending on where the bad bacteria are. If there is SIBO problems can start much sooner. Always assume you have some degree of fructose and lactose intolerance and consume these foods in very strict moderation (unless you have symptoms, in which case you should avoid them completely).

Remember that everyone can malabsob carbohydrates if they consume too much at once, or consume them in liquid form.

Both The Gut Health Protocol and Phage Complete can help with this issue by rebalancing the microbiome and helping to eliminate the bacteria that feed on the malabsorbed sugars. Building up the beneficial bacteria in the gut can also help repair the brush-border cells that make the enzymes that break down these sugars.

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