The Phloem Study (1999-2000)

To address the question of the antioxidant function of catechins on total serum and isolated lipoproteins, we conducted a long-term placebo-controlled supplementation study in which phloem was used as the source of catechins.

Seventy-five non-smoking male volunteers aged 31-70 years were recruited from the Kuopio area in eastern Finland through newspaper advertisements. Potential participants were screened in an initial telephone interview for the following inclusion criteria by a public health nurse: 1) no severe obesity (body mass index, BMI < 32 kg/m2), 2) elevated serum cholesterol concentration (total cholesterol 6-9 mmol/L), 3) no regular use of any drug or supplement with antioxidative (ß-carotene, vitamins C or E) or lipid lowering properties 4) no chronic diseases like diabetes, CHD or other major illness 5) willingness to consume 70 g of dried rye bread per day for four weeks. All criteria were ascertained prior to entering the study by a physician. A written informed consent was obtained from all participants. The study protocol was approved by the joint ethical committee for human research at the University of Kuopio and the Kuopio University Hospital.

The study was a 4 wk randomized double-blind supplementation study. Subjects were randomly assigned to consume daily 70 grams of normal dried rye bread (placebo group, n = 30), rye bread in which 7% of the rye flour was substituted with phloem powder (low catechin, LC group, n = 30) or bread in which 14% of the rye flour was substituted with phloem powder (high catechin, HC group, n = 15). The placebo group received 0.6 mg, LC group 17.7 mg and HC group 35.8 mg of catechins daily from the study bread. The subjects were advised to discontinue the use of tea, red wine, cacao and chocolate one week prior to the study and to avoid the use of alcohol and analgesics three days before and vigorous physical activity one day before the study visits. A four-day food recording was required before and during the last week of the intervention period to control for possible confounding factors and to check the compliance to given instructions. The compliance was also checked by a questionnaire designed to assess the amount of breads eaten. Blood samples were drawn after overnight fast (10 hours). All measurement were done at baseline and after the 4 wk supplementation period.

In the phloem study the lipid peroxidation was evaluated by measuring the oxidation susceptibility of serum and LDL+VLDL to oxidation.

We also analyzed the lignan content of phloem powder enriched rye bread and studied the dose-response relationship of the effect of dietary plant lignans derived from phloem on enterolactone production by measuring enterolactone concentration in serum. We found a significant increase in serum enterolactone concentration in the LP and HP groups compared with the placebo group (P=0.009 and P=0.003, respectively). Considerable interindividual differences were observed in the response to dietary lignans within the study groups.

Our results indicated that plant lignans attached to insoluble fiber layer in phloem can be further metabolized and converted to enterolactone presumably by the bacteria present in the colon.

More information: jaakko.mursu at uef.fi

Our publications:

Mursu J, Vanharanta M, Voutilainen S, Rissanen TH, Nurmi T, Porkkala-Sarataho E, Nyyssönen K, Virtanen JK, Salonen R, Salonen JT. Polyphenol-rich phloem enhances the resistance of total serum lipids to oxidation in men. Journal of Agriculture and Food Chemistry 2005;53:3017-22.

Vanharanta M, Mursu J, Nurmi T, Voutilainen S, Rissanen TH, Salonen R, Adlercreutz H, Salonen JT. Phloem fortification in rye bread elevates serum enterolactone level. European Journal of Clinical Nutrition 2002;56:952-57.

Mursu J, Nurmi T, Vanharanta M, Voutilainen S, Salonen JT. Developing phytochemical products: a case study. Phytochemical Functional Foods, Edited by Ian Johnson and Gary Williamson, Cambridge, England, 2003. ISBN 0-8493-1754-1.