Lipid digestion: orlistat: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Lipid digestion: orlistat

Sample item

A 40-year-old woman with obesity is started on orlistat. After some weeks she complains of oily, foul-smelling stools and has reduced vitamin D and vitamin K levels. Which mechanism accounts for this?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Inhibition of gastric and pancreatic lipases, which reduces triglyceride hydrolysis and fat absorption

Orlistat covalently binds the active serine of gastric and pancreatic lipases. About a third of dietary fat escapes hydrolysis and is passed in the stool, and the absorption of fat-soluble vitamins A, D, E and K falls. Supplementation with a multivitamin is advised.

Option by option

  • A. Inhibition of the sodium-glucose cotransporter in the proximal tubule

    SGLT2 inhibition is the mechanism of gliflozins and causes glycosuria.

  • B. Inhibition of acyl-CoA:cholesterol acyltransferase in enterocytes

    ACAT inhibition is not the mechanism of orlistat and does not cause oily stools.

  • C. Inhibition of gastric and pancreatic lipases, which reduces triglyceride hydrolysis and fat absorption (correct)

    Lipase inhibition causes steatorrhoea and fat-soluble vitamin malabsorption.

  • D. Binding of bile acids in the ileum, preventing their reabsorption

    Bile acid binding is the mechanism of resins, and these cause constipation and bloating rather than orlistat-type steatorrhoea.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Inhibition of gastric and pancreatic lipases, which reduces triglyceride hydrolysis and fat absorption. Orlistat covalently binds the active serine of gastric and pancreatic lipases.

Why is "Inhibition of the sodium-glucose cotransporter in the proximal tubule" not the answer?

SGLT2 inhibition is the mechanism of gliflozins and causes glycosuria.

Why is "Inhibition of acyl-CoA:cholesterol acyltransferase in enterocytes" not the answer?

ACAT inhibition is not the mechanism of orlistat and does not cause oily stools.

Why is "Binding of bile acids in the ileum, preventing their reabsorption" not the answer?

Bile acid binding is the mechanism of resins, and these cause constipation and bloating rather than orlistat-type steatorrhoea.

What concept does this question test?

It tests Lipid digestion: orlistat in Biochemistry. About a third of dietary fat escapes hydrolysis and is passed in the stool, and the absorption of fat-soluble vitamins A, D, E and K falls. Supplementation with a multivitamin is advised.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Lipid digestion: orlistat?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.