Questions: Dietary Fats, Fatty Acids, and Cholesterol

Question 1

Which type of dietary fat is most strongly associated with raising LDL cholesterol and increasing cardiovascular disease risk?

• A. Monounsaturated fatty acids (e.g., olive oil)
• B. Omega-3 polyunsaturated fatty acids (e.g., fish oil)
• C. Trans fatty acids (e.g., partially hydrogenated oils)
• D. Omega-6 polyunsaturated fatty acids (e.g., sunflower oil)

Answer: (C)

Trans fatty acids are uniquely harmful because they both raise LDL ('bad') cholesterol and lower HDL ('good') cholesterol, a double adverse effect not seen with saturated fat alone. Monounsaturated and omega-3 fats are generally considered cardioprotective. This distinction is why regulatory agencies have largely banned partially hydrogenated oils.

Question 2

Eating foods high in dietary cholesterol (like eggs) is the primary driver of elevated blood cholesterol in most people.

• T. True
• F. False

Answer: False

For most people, the liver compensates for dietary cholesterol by downregulating its own production — a process called feedback regulation. The primary dietary drivers of elevated LDL cholesterol are saturated and trans fats, not dietary cholesterol itself. A minority of people ('hyper-responders') do show a meaningful blood cholesterol rise from dietary cholesterol, but this is not the norm.

Question 3

Why are omega-3 and omega-6 fatty acids called 'essential' fatty acids, and what structural feature makes them impossible for the body to synthesize?

Model answer: They are called essential because the human body cannot synthesize them and must obtain them from diet. The body lacks the delta-12 and delta-15 desaturase enzymes needed to introduce double bonds at the omega-6 and omega-3 positions of a fatty acid chain — all double bonds the body can introduce are closer to the carboxyl end.

The body can elongate and further desaturate fatty acids once the omega-3 or omega-6 double bond exists, which is why consuming the parent forms (linoleic acid and alpha-linolenic acid) is sufficient. The essentiality is about the inability to create that first double bond at the correct position — a specific enzymatic gap, not a general inability to work with unsaturated fats.