A 56-year-old man came to see me with a very specific complaint: Every time he ate fatty food, he felt terrible. Nuts, salmon, sardines, dairy, meat – all produced bloating, cramping, and softer stools. He was sure he had “fat malabsorption” and wanted me to figure out why.
There were a few possibilities to explain his symptoms: moderate diverticulosis on colonoscopy; a diagnosis of mild ulcerative colitis in the past; and several rounds of the antibiotic rifaximin for a positive SIBO test.
But once a diagnosis appears in the chart, there’s a tendency to make the symptoms fit the diagnosis instead of asking whether the diagnosis fits the symptoms.
Revisit the Symptoms
Diverticulosis can definitely cause bloating and altered bowel habits, so I recommended a standard approach that included a high-fiber diet, increased hydration, and psyllium to improve colonic emptying. But instead of resolving his symptoms, he felt worse: cramping and multiple loose bowel movements. This wasn’t failure – it was information – and forced us back to the original question:
What were the symptoms that brought him in? Not “diverticulosis.” Not “SIBO.” Not even “fat malabsorption.” The symptoms were:
I eat fatty food, and then I bloat, cramp, and have loose stool.
And this is where the investigation needs to start.
Don’t Marry the Diagnosis
A diagnosis is only useful if it explains what’s actually happening. Sometimes a condition is real but incidental. Sometimes it explains only part of the picture. And sometimes the diagnosis itself is wrong. Diverticulosis was present, but treating it didn’t improve his symptoms, and a repeat colonoscopy showed he didn’t actually have ulcerative colitis. (Review of previous biopsies showed inflammation associated with his diverticulosis that was misdiagnosed as ulcerative colitis.)
Rather than continuing to unsuccessfully treat the conditions listed in his chart, the next step was to investigate the symptom pattern more directly. The main organ responsible for processing fat is the pancreas, so that’s where I started: a stool test for pancreatic function, a blood test for pancreatic enzyme levels, a CAT scan of the abdomen to image the pancreas, and most importantly – and inconveniently: 3 days of poo collection on a high fat diet to determine whether malabsorption was truly present (defined as >7grams of fat/24 hours).
I have to admit, I was doubtful about the diagnosis, because while he definitely had symptoms, he was missing the two most characteristic ones in people with fat malabsorption: foul-smelling floating stools and weight loss.
Good medicine isn’t about an expedient diagnosis. It’s about staying curious enough to notice when the diagnosis and the symptoms don’t line up.
All the testing came back negative; his 72 hour fecal fat test was well within normal limits, and so was everything else. And then I had a thought. What if this wasn’t an intrinsic problem with his gut, but something external that was irritating it? After convincing him to do one final stool test, we had the answer.
Giardia. A tiny parasite spread from person to person through food, water, or contaminated surfaces. While most people have symptoms that last just a couple weeks, about 30% develop chronic GI issues that can persist for years after the original infection. And this time, not only did his symptoms match his diagnosis, but the treatment made him better, not worse.
Bottom Line: Start with the symptoms. The diagnosis comes second.
