What’s so great about wholegrain bread?

October 17, 2013 - 06:33

Wholemeal bread has become generally accepted as the healthy alternative to bread made from refined white flour. A new study with pigs, bread-baking and fancy technology brings us closer to an answer to why this is so.

Improved digestion, lower cholesterol levels and a slower absorption of blood sugar were just some of the beneficial effects that dark bread had on the pigs in the study. (Photo: Shutterstock)

The latest dietary guidelines say it, health gurus say it and restaurants are keen to flaunt the message – choose wholemeal bread and whole grains. But what exactly is it that makes dark bread healthier than white bread?

A new study Aarhus University, Denmark, has taken a closer look at this question.

In the study, postdoc fellow Natalja Nørskov of the Department of Animal Science fed pigs with white bread and wholemeal bread to investigate what effect the two types of bread had on the pigs. She used pigs in her study, as their digestive system is similar to our own.

Fibres improve digestion and prevent obesity

White bread has undergone a greater degree of processing, so that the fibre-rich parts of the grain have disappeared. This means that the germ and the bran in the grain disappear too, leaving only few of the nutritional 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 compound,” says Nørskov.

Fibres have some positive health effects in their own right, as they have been shown to increase the viscosity in the gastrointestinal tract. They also increase satiety and slow down the absorption of blood sugar. This is good news for obese people and type 2 diabetes patients, since the higher viscosity also leads to a lower uptake of fat and cholesterol, and increases the excretion of bile acids.

Pigs feel the health effects of dark bread

The pigs were fed bread baked on refined flour, wholegrain wheat flour or wholegrain rye flour with added rye bran and wheat aleurone (wheat bran). Blood and urine samples were taken 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.

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 compound.
Natalja Nørskov

The metabolic responses also showed that there is a relationship between the presence of anti-oxidants and the inhibition of oxidation. Nørskov found that specific phenolic acids (ferulic acid and caffeic acid) were more readily available to pigs fed with 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 to 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 Nørskov.

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

Is dark bread always better than white bread?

This may sound as if we should always pick wholegrain bread, regardless of the situation. So does that render white bread useless?

“It depends on what you’re using it for,” says the researcher.

“If you’re going out for a run, you can get a lot of quick energy by eating white bread, but if you want to lose weight or prevent some of the many lifestyle diseases that we’re currently seeing in the western world, then wholemeal bread is the right choice.

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Read the Danish version of this article at videnskab.dk

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