Phytosterols. Effect of intake on cholesterol absorption and colorectal cancer risk

Abstract

Phytosterols are lipid components of all food items of plant origin. They are effective in decreasing plasma cholesterol concentrations, but have also been suggested to protect against colorectal cancer. The overall aims of the thesis were to describe and compare the physiological response after ingestion of two esterified sources of phytosterols, soy sterols and sitostanol from wood oil, and to describe the dietary intake of phytosterols with special emphasis on its relation to colorectal cancer risk.Seven ileostomy subjects consumed a controlled diet during three randomized periods of 3 days each. A controlled basal diet was served in all periods, and in two of the periods, 2.5 g of soy sterol esters or sitostanol ester were added. Effluent bags were gathered during the second and third day, pooled together from each 24 h-period, and analyzed for neutral and acidic sterols. Cholesterol absorption was measured by the classical double label method. The results showed that soy sterol esters and sitostanol ester decreased cholesterol absorption from 58 % in the control period, to 39 and 38 %, respectively. The esterification of the unsaturated and saturated phytosterols gave them similar inhibiting properties on cholesterol absorption. The study showed no significant decrease in sterol excretion, which might be due to low power of the study.A database on the phytosterol content of different foods was developed for use in epidemiological studies. It was applied within the framework of the Netherlands Cohort Study on Diet and Cancer among 120,852 subjects who completed a baseline questionnaire in 1986. After 6.3 years of follow-up, 620 colon and 344 rectal cancer cases were detected. A case-cohort approach was used to calculate confounder adjusted rate ratios (RR) and the 95 % confidence intervals (CI) for quintiles of phytosterol intake. The major sources were bread (38 %), vegetable fats (26 %), and fruits and vegetables (21 %). For men and women, there was no clear association between intake of any of the phytosterols and colon cancer risk when adjusting for age, smoking, alcohol, family history of colorectal cancer, education, and cholecystectomy. Energy adjustment did not alter the results. For rectal cancer in men, energy adjustment gave positive associations for campesterol and stigmasterol. For women, no association was observed between the dietary intake of any of the phytosterols and rectal cancer risk .