Effects of cooking using multi-ply cookware on absorption of potassium and vitamins: a randomized double-blind placebo control study

Abstract

This 2-week interventional study involved a randomized allocation of subjects into three groups: Group A (daily ingestion of 350 g vegetables cooked without water using multi-ply [multilayer-structured] cookware), Group B (daily ingestion of 350 g vegetables; ordinary cookware) and Group C (routine living). Before and after intervention, each subject underwent health examination with 24-h urine sampling. Blood vitamin C significantly increased after intervention from the baseline in Group A (P < 0.01) and Group B (P < 0.05). β-Carotene levels also increased significantly after intervention in Group A (P < 0.01) and Group B (P < 0.01). Oxidized low-density lipoprotein decreased significantly after intervention in Group A (P < 0.01). In Group A, 24-h urinary potassium excretion increased significantly (P < 0.01) and 24-h urinary sodium (Na)/K ratio improved significantly (P < 0.05) after intervention. In conclusion, a cooking method modification with multi-ply cookware improved absorption of nutrients from vegetables and enhanced effective utilization of the antioxidant potentials of vegetable nutrients.

Keywords::

• vegetable ingestion
• water-free cooking
• 24-h urinary Na/K
• vitamin C
• β-carotene
• oxidized LDL

Acknowledgements

The authors are indebted to Vitacraft Japan Co. Ltd for the free-of-charge supply of cooking devices used for this study, to Ikari Supermarket Co. Ltd for the supply of vegetables to each subject and to Ms Reina Shoji, Ms Erina Joh, Ms Shiho Li and Mr Isshiki Tanemura and others involved in the study at Prof. Tsuda's and Prof. Toshio Moritani's Laboratories of Kyoto University Graduate School of Human and Environmental Studies for their cooperation in the study.

Declaration of interest: The authors declare that they have no conflict of interest. Cookware and vegetables were supplied free of charge with no obligation from the researchers to the manufacturers; the manufacturers were willing to voluntarily contribute towards food education for students. Funds for the blood or urine analysis were self-funded.

Affiliations

All authors were involved in the concept and design of this study. AH and HM collected the data and performed the nutritional analyses. YY and KT assessed the quality of study design and the data independently. MM performed the statistical analysis and wrote the manuscript. All authors critically reviewed the manuscript and approved the final version submitted for publication.