It is not always an advantage to be refined – at least not when it comes to flour. Refined flour is certainly fine and white, but it is generally accepted that the coarser wholegrain flour has health benefits that the white flour just cannot match. The question is why this is so.

Scientists from Aarhus University have used bread-baking, pigs and high-tech to unveil some of the secrets of the virtues of wholegrain flour. They found that the digestive system reacts differently and produces different compounds depending on whether the intake is wholegrain flour or refined flour.

The essential bread

Flour and bread play a major role in our diet.

- In the western world, bread makes up half of our intake of carbohydrates, 50-60 per cent of our intake of vitamin B and a third of our intake of protein. Wheat and rye are suitable for baking bread and are therefore very important to us, says postdoc Natalja Nørskov from the Department of Animal Science at Aarhus University.

In her PhD study she examined whether there are specific bioactive compounds in wholegrain flour and refined flour that may help explain why wholegrain is healthier. She used the so-called LC-MS metabolomics technology to study the degradation products in the body after you have eaten bread baked on different types of flour. With LC-MS metabolomics you get a snapshot of the entire scenario in one go rather than having to analyse each compound separately.

Fibre is the source of all good

Wheat and rye are good sources of fibre and minerals, vitamins and health-promoting plant chemicals. The processing action is what makes a difference between refined flour and wholegrain flour. When the flour is processed, the fibre-rich part of the grain is removed. But along with the fibre disappears the germ and the bran and it is here that you have the highest concentrations of beneficial bioactive compounds.

- Refined flour and wholegrain flour contain the same level of carbohydrates, but the refined flour contains some empty calories – in other words, energy without significant amounts of fibre and bioactive compounds, says Natalja Nørskov.

Fibre itself has some positive effects on health. It has been shown to increase the viscosity in the gastrointestinal tract; it increases satiety and slows the absorption of blood sugar. This is good news for type 2 diabetes patients. The higher viscosity also leads to a lower uptake of fat and cholesterol, and increased excretion of bile acids. This is good news for high cholesterol sufferers.

- A high content of fibre in the diet is linked to a lower incidence of cardiovascular disease, type 2 diabetes and some types of cancer. However, this inverse relation between the intake of fibre and the development of a disease is not the same as saying that there is a direct link. It says nothing about the health-promoting mechanisms involved, explains Natalja Nørskov about the background for her studies.

Different breads gave different results

In her experiments Natalja Nørskov used pigs as a model for human subjects, because of similarities in their digestive systems. The pigs were fed bread baked on, respectively, refined flour, wholegrain wheat flour or wholegrain rye flour with added rye bran and wheat aleurone (wheat bran). Blood and urine samples were taken in order to examine the biochemical effects produced by the different types of bread – and different concentrations of various  compounds were found in blood and  urine, which mirrored the differences in the loaves.

The identified metabolites could be classified into three groups: fatty acids, bile acids and phenols. Their concentrations in pig plasma and urine could be related to diet and to possible health effects. The metabolic responses also showed that there is a relationship between the presence of anti-oxidants and inhibition of oxidation. Natalja Nørskov found, among other things, that specific phenolic acids (ferulic acid and caffeic acid) were more readily available to pigs fed fibre-rich bread. Phenolic acids act as natural antioxidants and may have health benefits in that they inhibit the oxidation of the fats in the body.

- The results show that it is important to eat unrefined carbohydrates and enrich bread with fibre-rich ingredients such as aleurone, but there is a need for more knowledge in the area – including the role of polyunsaturated fatty acids and their enzymes and their behaviour during the milling, baking and storage processes, says Natalja Nørskov, and continues:

- Living plants contain natural antioxidants, which inhibit the oxidation of fats. But in products such as flour and bread the polyunsaturated fatty acids are oxidized within hours or days, leading to the formation of oxylipins,   compounds whose effect on health we do not yet know.

For further information please contact: Postdoc Natalja Nørskov, Department of Animal Science, e-mail: Natalja.Norskov@agrsci.dk, telephone: +45 8715 7967