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A Primal Primer: FODMAPs

You could be having a fairly routine conversation about health and nutrition where everything discussed is familiar. You hear things like “carbs [7]” and “medium chain triglycerides [8]” and “fructose” and “macros” and “gluten [9]” and “PUFAs [10],” thinking nothing of it. Like I said, routine. Then someone mentions FODMAPs. Huh? What the heck is that? Quite possibly one of the strangest, seemingly contrived acronyms in existence, FODMAPs represents a collection of foods to which a surprisingly large number of people are highly sensitive. To them, paying attention to the FODMAPs in their diets is very real and very serious if they hope to avoid debilitating, embarrassing, and painful digestive issues.

To begin, what exactly are FODMAPs?

As I said, it’s an acronym:

F is for Fermentable – Fermentable carbohydrates are carbohydrates that are fermented by bacteria instead of broken down by our digestive enzymes. In most people, some fermentable carbohydrates are healthy sources of food for the (helpful) bacteria that ferment them; these can include the prebiotics [11] I’ve championed in the past and can actually improve digestive and overall health. In people with FODMAPs intolerance, certain carbohydrates can become too fermentable, resulting in gas, bloating, pain, and poor digestion, as well as proliferation of unwanted pathogenic bacteria.

O is for Oligosaccharides – Oligosaccharides are short-chain carbohydrates, including fructans (fructooligosaccharides, or FOS, and inulin) and galactans (raffinose and stachyose). Fructans are chains of fructose with a glucose molecule at the end; galactans are chains of galactose with a fructose molecule.

D is for Disaccharides – These are pairs of sugar molecules, with the most problematic being the milk sugar lactose (a galactose molecule with a glucose molecule).

M is for Monosaccharides – This describes a single sugar molecule. Free fructose is the monosaccharide to watch out for with FODMAPs intolerance.

A is for And – Every list needs a good conjunction.

P is for Polyols – Polyols include sugar alcohols like xylitol, sorbitol, or maltitol. For an idea as to their effects, type one of them into Google and note the autofill choice (hint: it’s usually “diarrhea” or “constipation” or “gas”). Since large amounts of polyols rarely occur in nature, lots of people have trouble with them.

Most people probably don’t need to worry about these categories. Most people enjoy pristine, effortless trips to the toilet that happen like clockwork and finish in under a minute. Heck, as I understand it, most people don’t even use toilet paper these days; they are that efficient and clean. Yes, it’s true: digestion worldwide has never been better!

The reality, of course, is that digestive difficulties are widespread, particularly in the industrialized world. If it’s not constipation, it’s diarrhea. Or bloating. Or gas. Or hemorrhoids. Or IBS. Or all of the above. These complaints are sadly very common [12] (even more common than those stats would suggest, since many people are too embarrassed to admit they have an issue). For many of these people, FODMAPs may be exacerbating their symptoms.

Normal carbohydrate digestion takes place in the small intestine, where polysaccharides are broken up into glucose, fructose, and galactose and transporters like GLUT2 and GLUT5 absorb them for the body to use as nutrients. Sometimes those sugar molecules make it past the small intestine into the large intestine where colonic bacteria – the gut flora [13] we (sorta) know and love – gobbles it up via fermentation, potentially causing gas [14] and painful bloating. The presence of too many sugars in the colon can also cause an influx of fluid, which could lead to diarrhea. Constipation is another common symptom, though it’s not clear exactly how FODMAPs cause it. And some polysaccharides, like the oligosaccharides, make it through to the colonic bacteria as a rule because they resist digestion in everyone (in healthy people, these have a useful prebiotic effect).

You might be thinking, “Cool, so I can just avoid those weird sounding sugars and be fine, right?” Probably not. FODMAPs are very prevalent in the food supply. Even if you avoid free fructose, don’t drink milk, and ditch processed food containing sugar alcohols, you’ll still run into them in many fruits and vegetables.

FODMAP-containing vegetables include:

Asparagus (fructose, fructans), artichoke (fructose), beets (fructans), broccoli (fructans), Brussels sprouts (fructans), butternut squash (fructans), cabbage (fructans), celery (polyols), cauliflower (polyols), eggplant, fennel (fructans), garlic (fructans), leek (fructans), mushroom (polyol), okra (fructans), onion (fructans), shallots (fructans), sweet corn (fructose), radicchio (fructans), sweet potato (polyol)

FODMAP-containing fruits:

Apples (fructose, polyol), apricots (polyol), avocados (polyol), blackberries (polyol), cherries (fructose, polyol), plums (polyol), pluots (polyol), lychees (polyol), nectarines (polyol), peaches (polyol), pears (fructose, polyol), persimmons (polyol), grapes (fructose), mango (fructose), watermelon (polyol, fructose), dried fruit (fructose), juice (fructose)

Plus sweeteners like honey [15], agave nectar, maltitol, sorbitol, mannitol, and xylitol. And any dairy that contains significant amounts of lactose, like milk [16] or soft cheeses [17]. Depending on your sensitivity, cream or butter [18] can even do the trick.

So it covers quite a few otherwise healthy Primal foods (and some non-Primal ones, like wheat and rye and the aforementioned refined sweeteners).

Let me reiterate before I go on, because I don’t want to scare everyone away from berries and broccoli: not everyone has problems with FODMAPs. Most people probably don’t. If you’re eating all that stuff without issue, continue doing so and consider this post merely an academic curiosity.

Who might benefit from limiting FODMAPs?

Anyone with small intestinal bacterial overgrowth (SIBO).

Normally, the small intestine has relatively low numbers of gut flora residents. In SIBO, it’s got tons that aren’t supposed to be there. They interfere with nutrient absorption, digestion, and just generally muck everything up. SIBO has been shown to correlate quite strongly with lactase deficiency [19]. Without enough lactase, you won’t be able to digest lactose (one of the premier FODMAPs) and your colonic bacteria will have to do the job. Another, earlier study found that patients with SIBO also show malabsorption of fructose and sorbitol in addition to lactose [20]; all three are FODMAPs.

Anyone with IBS.

Low-FODMAP diets beat the pants off  [21]conventional dietary advice for people with IBS. One study [22] found that while healthy subjects had increased flatulence on a high-FODMAP diet, subjects with IBS had increased flatulence in addition to lethargy and adverse GI symptoms. This could indicate that both groups were feeding FODMAPs to their gut bugs (which produce the flatulence through fermentation), but only the IBS patients had enough pathogenic gut flora to produce adverse symptoms.

Anyone suffering from chronic stress.

Stress is a well-known disruptor of digestive function as anyone who’s gotten queasy, lost their appetite, or had explosive diarrhea before the big interview could tell you. There’s evidence that stress might be causing FODMAP-intolerance, too. First, stress inhibits the action of GLUT2 [23], a transporter responsible for the small intestinal absorption of glucose, fructose, and galactose in the gut. If you’re unable to adequately absorb the sugar molecules in the small intestine, they end up making it to your large intestine for fermentation by colonic bacteria. Second, stress has an immediate impact on the composition and function of your gut flora [24], rendering your populations less diverse and allowing certain pathogenic species to overpopulate.

Anyone with otherwise unexplained digestive problems.

Maybe you haven’t had a diagnosis. Maybe you just don’t feel right after eating almost anything. Maybe you’re chronically constipated (or the opposite). Trying a low-FODMAP diet can help you narrow your focus and start to identify some culprits.

If you decide to embark on a low-FODMAP diet, consider keeping a diet journal [25] to log your food and track your reactions to individual FODMAPs. Some people might really react poorly to fructose while having no issues with lactose. Point being: different FODMAPs affect different people differently. You can tolerate some and not others.

Dosage matters, too. A gram of inulin might be fine, while five grams could cause distress. Individual tolerance must be determined by, well, seeing what and how much you tolerate.

If you’re interested in healing your gut, whether from SIBO or IBS or anything else that might be predisposing you to FODMAP intolerance, well-established protocol like GAPS [26] (Gut and Psychology Syndrome) diet or SCD [27] (specific carbohydrate diet) may help and are worth looking into. 

If you have no digestive issues, I would caution against trying a low-FODMAP diet “just because.” You’ll be missing out on some very nutritious, important foods, probably unnecessarily, while adding a bunch of unnecessary stress to your eating. FODMAP-related digestive issues are very noticeable. You’ll know it if you have it.

Well, that about sums it up. I hope this basic Primal Primer was helpful for you.

Now that we’re done, what about you? Do you have any sensitivities to FODMAPs? Has looking at that list of FODMAP foods made lightbulbs go off? Let me know below!