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No two gastrointestinal tracts are alike. I bet you’ve never heard an article with that opening line. But it’s true, the hollow organs that make up your GI tract- mouth, esophagus, stomach, small intestine, large intestine, and rectum- can differ slightly in structure and functionality from person to person. These organs determine how well food can be digested and absorbed. The amount of acid you stomach produces, the absorptive capacity of the epithelial cells in your small intestine, and the kind and quantity of bacteria in your large intestine, are examples of how digestive capabilities are dependent on several elements. The presence of functional bowel disorders, such as constipation, diarrhea, IBS, use of NSAIDs, antibiotics, or other medications, digestive motility, and level of inflammation from GI diseases (ulcerative colitis or Crohn’s) can impact the types of food that one can tolerate. Personalizing nutrition to the individual is key for preventing and managing symptoms of GI conditions in addition to symptoms of chronic disease.

Ordovas et al. defines personalized nutrition as “an approach that uses information on individual characteristics to develop targeted nutritional advice, products, or services.”1 A one-size-fits all paradigm does not apply to nutrition. It is why government officials and health-care professionals offer nutrition “guidance” rather than concrete protocols or meal plans. Personalization of nutrition interventions is necessary to maximize “the benefits and [reduce] the adverse effects of dietary changes for the individual.”1 Basically, nutrition intake that doesn’t align with an individual’s needs can do more harm than good.

How Digestion Influences Our Nutrition Needs

Oftentimes gastrointestinal function, or lack thereof, determines how well someone digests and absorbs (the nutrients of) certain foods. Functional GI-disorders (FGID) are due to disorders of the gut-brain axis, basically how your brain sends signals to the nerves in your gut. The symptoms of FGID can be incredibly bothersome to the person experiencing them; symptoms include, but are not limited to, constipation, diarrhea, pain, bloating, and difficulty swallowing.5 For this reason, symptom management via personalized nutrition interventions can vastly improve a person’s day to day wellbeing and comfort-level.

Let’s talk about some of these disorders and how different dietary interventions can help or hurt symptoms of them.


There are many reasons why one might experience constipation, including lack of fiber, irritable bowel syndrome (IBS), gastroparesis (slow-motility), opioid-induced constipation (OIC), and pelvic floor dysfunction (PFD). Even if you eat a high fiber diet, it’s still possible to get constipated if you create more stool than your body can excrete in a day.

The dietary interventions for constipation will differ slightly depending on the cause of constipation. For example, if you have PFD, fiber and laxatives can worsen symptoms. But if you have IBS-related constipation or gastroparesis-induced constipation, then over-the-counter laxatives, and increased fiber intake (food or supplements) can help. Two opposing solutions for the same apparent problem!

Gastroparesis-induced constipation is common in individuals with chronic high blood sugar or diabetes, meaning high blood sugar can cause a slowing down of the GI tract, which can lead to constipation.

Generally, it is recommended that a high fiber and low glycemic diet is followed if you have diabetes. However, a high fiber diet can exacerbate gastroparesis since fiber takes longer to digest and there is already slowed motility. The solution to this double whammy of high-blood sugar induced gastroparesis and gastroparesis-induced constipation is to modify the texture of high fiber, low-glycemic foods. For example, pureed parsnips and fennel are more easily digested since their particle size is reduced prior to digestion.

To add one more level of diet confusion, I meant diet “personalization,” high fiber, low glycemic carbohydrates are often not well tolerated by those with irritable bowel syndrome (IBS). The diet of someone with IBS versus someone with diabetes will differ according to personal tolerance and acceptability.

Irritable Bowel Syndrome (IBS)

IBS side effects include severe pain, bloating, and bowel changes after ingesting certain short-chain carbohydrates, known as FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). With functional bowel disorders, which is just a fancy way of saying that with there is no apparent inflammation or structural issue with the intestines, dietary changes are made according to symptoms. A diagnosis of IBS requires a high level of diet personalization; and dietary management can resolve or reduce many of the unpleasant symptoms. One person with IBS might be able to consume disaccharides, such as lactose, but not foods containing polyols, such as cauliflower.

And personalization of dietary intake with IBS applies not only to the type of food, but the quantity.  Tolerance of certain foods can vary according to dose. For example, someone could experience no adverse symptoms after eating half a clove of garlic, but one clove could cause bloating, gas, and pain.

Portion sizes are also modified for individuals experiencing dyspepsia, another functional disorder. 

Functional Dyspepsia (indigestion)

One in four people in the United States experience indigestion, known as dyspepsia in the medical world. Non-ulcer or -GERD induced indigestion can be a result of going too long in between meals, eating high volume or high fat meals, and drinking alcohol (particularly on an empty stomach). Dietary interventions include not going too long in between meals without eating, eating smaller low-fat meals, and avoiding alcohol on an empty stomach.

Smaller, more frequent meals can manage symptoms of dyspepsia but could exacerbate symptoms in someone who has constipation. It is recommended that those with constipation eat larger, fewer meals throughout the day. Large, bulky meals trigger the gastrocolic reflex, which controls the movement of the lower intestinal tract after a meal.6

After reading this, you’re most likely overwhelmed by all the dietary modifications. Nutrition is nuanced! A recommendation that might be appropriate for one condition could exacerbate another. Many seemingly unrelated conditions also tend to impact the gut in one way or another. Therefore, type of intake, quantity, and timing of food are all important considerations when managing symptoms.

It’s personal, but in a good way!


1) Ordovas JM, Ferguson LR, Tai ES, Mathers JC. Personalised nutrition and health. BMJ. 2018;361:bmj.k2173. Published 2018 Jun 13. doi:10.1136/bmj.k2173

2) Mahadeva S, Goh KL. Epidemiology of functional dyspepsia: a global perspective. World J Gastroenterol. 2006;12(17):2661-2666. doi:10.3748/wjg.v12.i17.2661

3) Definition & Facts of Indigestion. National Institute of Diabetes and Digestive and Kidney Diseases.,the%20United%20States%20each%20year.&text=Of%20those%20people%20with%20indigestion,are%20diagnosed%20with%20functional%20dyspepsia.

4) Aboubakr A, Cohen MS. Functional Bowel Disease. Clin Geriatr Med. 2021 Feb;37(1):119-129. doi: 10.1016/j.cger.2020.08.009. Epub 2020 Nov 2. PMID: 33213766.

5) Fikree A, Byrne P. Management of functional gastrointestinal disorders. Clin Med (Lond). 2021;21(1):44-52. doi:10.7861/clinmed.2020-0980

6) Malone JC, Thavamani A. Physiology, Gastrocolic Reflex. [Updated 2021 May 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: