Kaplan USMLE Step 1: What nutrient is elevating blood pressure?

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

The AMA and Kaplan have teamed up to support you in reaching your goal of passing the USMLE® or COMLEX-USA®. If you're looking for additional resources, Kaplan provides free access to tools for pre-clinical studies, including Kaplan’s Lecture Notes series, Integrated Vignettes, Shelf Prep and more. 

A 38-year-old woman comes to the physician for a routine health maintenance examination. She has two children and no significant medical history. She has had no major changes in her health over the past year, but she has started a new role in her career as a lawyer and has been much busier than in the past.

She describes frustration with the lack of time to exercise and prepare healthy meals, and she has been eating fast food more often than she would like. She has additionally started drinking multiple sodas during the day to keep up with her workload. Her blood pressure, as measured in the physician office, is 133/97 mm Hg, elevated from her previous readings. Her weight has remained stable at 62 kg (137 pounds) and her body mass index is 27 kg/m².

Excess consumption of what nutrient is most likely directly contributing to her elevated blood pressure?

A. Animal protein.

B. Fructose.

C. Insoluble fiber.

D. Saturated fat.

E. Sodium.

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The correct answer is B.

Basic science and clinical data have implicated excess fructose consumption as being a primary driver of the early pathogenesis of metabolic syndrome and essential hypertension. The mechanism is related to increased production of uric acid, which is the mediator of pre-glomerular microvascular injury, resulting in the salt-sensitive essential hypertension. 

Specifically, uric acid increases plasma renin levels, thereby activating the renin-angiotensin-aldosterone system, as well as causing vascular smooth muscle proliferation and atherosclerotic changes in the pre-renal vasculature.

Excess consumption of fructose has been shown to induce hypertension in as little as a week, with the effect relieved by uric acid lowering therapy. Common sources of fructose in the standard U.S. diet are soda, sweetened pastries and other sources of sugar. High-fructose corn syrup is 55% fructose plus 45% glucose, compared to regular table sugar which is 50:50.

Choice A: Although animal protein was previously thought to be associated with kidney damage, this is not the case in individuals with healthy kidneys. Lean sources of animal protein are part of a healthy diet and are not associated with the development of essential hypertension.