Phytosterols are absorbed and transported in chylomicrons as efficiently as cholesterol itself.
options: True False
The correct answer and explanation is:
The correct answer is: False
Explanation:
Phytosterols are plant-derived sterols structurally similar to cholesterol, found in foods such as vegetable oils, nuts, seeds, and whole grains. Despite their structural similarity to cholesterol, phytosterols differ significantly in how they are absorbed and transported in the human body.
Absorption Efficiency:
Phytosterols are absorbed by the intestine much less efficiently than cholesterol. While cholesterol absorption rates typically range between 40-60%, phytosterols have an absorption efficiency of only about 0.5-2%. This dramatic difference is due to several factors:
- Intestinal Transporters: Both cholesterol and phytosterols are taken up by enterocytes (intestinal cells) via transporters such as Niemann-Pick C1-like 1 (NPC1L1). However, once inside the enterocyte, phytosterols are preferentially transported back into the intestinal lumen by ATP-binding cassette transporters (ABCG5 and ABCG8), which actively pump phytosterols out to prevent excessive absorption. Cholesterol, by contrast, is retained more effectively.
Transport in Chylomicrons:
After absorption, cholesterol is incorporated into chylomicrons, which transport lipids from the intestine through the lymphatic system into the bloodstream. Phytosterols are also incorporated into chylomicrons but at much lower levels because of their low absorption.
Physiological Implication:
This low absorption and rapid excretion of phytosterols are important for human health. Phytosterols compete with cholesterol for absorption and can reduce cholesterol uptake, which is why phytosterol-enriched foods are used to help lower LDL cholesterol levels.
Summary:
- Cholesterol absorption: ~40-60%
- Phytosterol absorption: ~0.5-2%
- Both can be transported in chylomicrons, but phytosterols are much less absorbed and hence present in lower amounts.
- Active efflux transporters limit phytosterol absorption.
Thus, phytosterols are not absorbed and transported in chylomicrons as efficiently as cholesterol itself, making the statement false.