Hardest RDN Practice Questions — Can You Answer These?

Honey contains fructose and glucose, which are reducing sugars. These possess a free reactive carbonyl group that reacts with amino acids in the Maillard reaction. Sucrose is a non-reducing sugar and does not participate until hydrolyzed. Fructose browns at lower temperatures than glucose. CDR Tip: The Maillard reaction requires a reducing sugar + an amino group; it is NOT the same as caramelization.

Sorbitol is a polyol (sugar alcohol). It is incompletely absorbed in the small intestine, creating an osmotic gradient that draws water into the colon (osmotic laxative effect). It is then fermented by colonic bacteria, producing gases (CO2, H2). CDR Tip: Polyols provide fewer calories (approx 1.6-2.6 kcal/g) but are high-FODMAP. Erythritol is better tolerated as it is mostly absorbed in the small intestine.

This forms Type 3 Resistant Starch (RS3), or retrograded starch. When starch is cooked (gelatinized) and then cooled, the amylose realigns into a crystalline form that resists enzymatic digestion in the small intestine. CDR Tip: RS1 is physically inaccessible (seeds); RS2 is ungelatinized (green bananas); RS4 is chemically modified. RS3 is the most clinically relevant for leftover starches.

Amylose is a linear, tightly packed molecule with less surface area, making it less accessible to alpha-amylase for digestion. Amylopectin’s highly branched structure provides numerous ends for rapid enzymatic hydrolysis into glucose. CDR Tip: High amylose = slower digestion = lower Glycemic Index (GI). This is a core concept for MNT in diabetes and weight management.

This is Dextrinization. Dry heat breaks down long starch polymers (amylose/amylopectin) into shorter-chain polysaccharides called dextrins. Dextrins have significantly less thickening power (viscosity) than the original starch but increased solubility and sweetness. CDR Tip: Wet heat leads to gelatinization (increased viscosity); dry heat leads to dextrinization (decreased viscosity).