Professor Samir Samman, Otago University
The importance of nutrient interactions was echoed by Professor Samir Samman who presented evidence on the impact of bioavailable zinc on risk of type 2 diabetes. Whilst the benefit of a diet high in dietary fibre is well established, emerging evidence suggests a positive association between zinc and reduced risk of type 2 diabetes. However, phytate, found in foods rich in dietary fibre, such as nuts, seeds, grains and cereal foods, inhibits zinc absorption.
Resolving this dilemma requires an holistic approach which Professor Samman along with Dr Garnett and colleagues explored in adolescents with type 2 diabetes. Using data from the Researching Effective Strategies to improve Insulin Sensitivity in children and Teenagers (RESIST) study, they compared bioavailable zinc intake in participants following the moderate carbohydrate, moderate protein diet with those on the high carbohydrate, low fat diet. Although absolute zinc intake was similar between the two diets, the ratio of phytate to zinc and the prevalence of inadequate zinc intake were higher on the high carbohydrate diet.
It is therefore important to consider the food source of dietary zinc. Indeed, the impact of zinc deficiency on growth was identified in Iranian adolescents low in zinc as a result of their high phytate diet. With this in mind, it is interesting to note a shift in dietary sources of zinc in Australian children from 1995 to 2007 from bioavailable zinc sources such as meat and dairy foods to less bioavailable sources.
Whilst the implications of these dietary changes are unclear, it highlights the risk of focusing on a single nutrient or food and the benefit of a meal-based approach to dietary advice. Professor Samman acknowledges that the phytate:zinc ratio is difficult to use in practice. Since the inhibitory effect of phytate occurs at the level of the meal, to optimise zinc bioavailability, he suggests having phytate-rich foods in separate meals to more bioavailable zinc sources. He also suggested the glycaemic index as a suitable measure of carbohydrate quality for managing glucose levels.
Professor Samman presented at the ‘Putting nutrition into meals’ symposium held on 28 April 2015 in Sydney.
Click here to access a webinar presentation of the symposium and a quiz contributing to CPD points under the APD ̶Professional Education-Assessed” CPD module is available.
The event was hosted by Nutrition Society of Australia, sponsored by Meat & Livestock Australia (MLA) and supported by Dietitians Association of Australia, Horticulture Innovation Australia, Egg Council, Dairy Australia, Grains and Legumes Nutrition Council. The topics attracted much interest with more than 600 people registering for this event.
Supported by Meat & Livestock Association