The results of the present work show that the subjects with SPDPI had higher symptom frequency and intensity when ingesting dairy products but also after ingesting non-dairy high FODMAP foods, compared with the subjects with SPDPT. Importantly, our analysis included patients with numerous gastrointestinal diagnoses, not evaluating a particular group, such as patients with irritable bowel syndrome. The study subjects were more similar to the population seen at gastroenterology consultations, as opposed to a particular segment of said population (13–16).
The aim of the present study was to find out if self-perceived dairy product intolerance was associated with intolerance to other types of FODMAPs, perceived through an increase in the frequency and intensity of abdominal symptoms. The analysis separated high FODMAP foods that also contained some amount of lactose, utilizing the rationale that lactose is not the only disaccharide that causes symptoms, and that said symptoms due to lactose are indistinguishable from those attributed to the consumption of other carbohydrates.
In the subjects with SPDPI (56%), bloating, abdominal pain, borborygmus, flatulence, and diarrhea were the most frequent symptoms. Bloating and flatulence stood out in the two groups, producing nonspecific symptoms that made it impossible to determine causality, as has been described in other reports (17). Sixty-five percent of the subjects with SPDPI had stopped drinking milk, in an attempt to mitigate their symptoms, without having undergone any test to confirm lactose malabsorption or intolerance. The figure clearly indicates that a large number of persons are in the SPDPI category and that they reduce or avoid dairy product consumption.
One of the striking findings of the present work underlines the fact that the subjects with SPDPI presented with more symptoms than the subjects with SPDPT, suggesting that subjects with one food intolerance could also have others. Subjects that consume delactosed products often state that consuming whole milk causes them discomfort, a conviction commonly heard in daily practice. However, even though patients with SPDPI consciously consume products that are low in lactose, they also consume a large quantity of dairy products or inadvertently consume other foods that contain lactose.
To better distinguish the effect of inadvertent dairy product consumption in subjects with SPDPI, foods were selected that contained fewer than 6.25 grams of lactose per portion. The subjects with SPDPI reported symptoms when they consumed practically any of the listed products. Thus, foods without lactose were shown to have an influence on symptoms in persons with SPDPI.
The results of the present study revealed that more than half of the subjects that had a gastroenterology consultation were in the SPDPI category and suppressed milk consumption.
Ours is the first study to examine the effect of the consumption of FODMAPs other than lactose on persons with SPDPI. The subjects with SPDPI had less tolerance for FODMAPs, excluding lactose, than the subjects with SPDPT and the highest scores in the SPDPI group were for legumes, peas, watermelon, onion, cranberries, mushrooms, and beets, all of which are high FODMAP foods.
In the SPDPT group, one-fourth of the persons stated they had symptoms after consuming onion, peas, beets, prunes, nectarines, soft drinks and sweetened juices, chai, mushrooms, legumes, and avocado. Of those subjects, 25% presented with a greater frequency of bloating, after ingesting foods with more than 5.5 g of lactose per portion, suggesting that there is a limit to the quantity of sugars the human organism can tolerate and that perhaps it is the result of a combination of sugars, rather than one particular sugar. Reports have shown that not all the patients with lactose malabsorption present with symptoms and that even patients with demonstrated hypolactasia tolerate up to 12 g of lactose per day with no problem (3,7,18).
A limitation of the present study is the fact that the number of portions of foods containing lactose that each individual consumed was not evaluated, nor was the temporal relation with the intake of the other FODMAPs assessed. Patients possibly had lower grades of hypolactasia that enabled them to consume moderate quantities of milk, with no problem, and that their discomfort was due to the combination of high FODMAP foods, including those with lactose (13).
We recognize that by not performing breath tests to confirm the diagnosis of lactose malabsorption, the documented correlation with the consumption of foods containing lactose could be overestimated. Nevertheless, it is pertinent to remember that at least 30% of the persons with SPDPI had hypolactasia that was demonstrated (19), thus SPDPI could be a good tool for motivating the search for malabsorption.
Memory bias was another limitation. Even though one study showed that the distressing symptoms caused by dairy product ingestion were not easily confused or forgotten (20), we do not know whether the survey participants really had a temporal association with dairy product consumption and the production of symptoms or if the symptoms were associated with the consumption of other high FODMAP products.
Another study limitation was the impossibility to analyze the effect of previously prescribed medications or whether the subjects followed a specific diet and their level of adherence to it. Thus, we could not establish definitive associations for our study findings.
Likewise, we recognize that the patients with gastrointestinal symptoms related to dairy product intolerance can present with small intestinal bacterial overgrowth (SIBO) that causes those symptoms (21). The fact that we did not carry out diagnostic tests for detecting SIBO was another study limitation.
Lastly, we are aware that we could not establish whether dairy products, by itself, or its combination with other fermentable sugar-rich foods, caused symptoms in the persons with SPDPI. However, we did demonstrate that those patients presented with distressing symptoms after consuming FODMAPs other than lactose, and that the simple fact of being thought to have SPDPI justifies a more thorough evaluation to determine the effect of other high fermentable sugar products on them.