White rye flour bread leads to better insulin and blood sugar levels than wheat bread with rye bran

Lund University Faculty of EngineeringFeb 12 2010

Wholegrain bread is good and good for you, as most people know. But it is not only the fiber-rich bran, the outer shell of the grain, that is healthful. On the contrary, research at the Lund University Faculty of Engineering shows that bread baked with white rye flour, which is flour made from the inner, white part of the rye kernel, leads to better insulin and blood sugar levels compared with wheat bread with rye bran. White rye flour thus leads to much better values than both regular wheat flour and rye bran. At the same time, much of the bread that is sold in stores today in most countries is in fact baked with wheat flour and bran from various grains.

The great difference between white rye and white wheat surprises the researchers.

"Precisely what it is that makes rye lead to a stable blood sugar curve is as yet unknown. But we are getting closer and closer to an answer. There are several different types of rye, and all not all types have the same effect, which means that some of them can be omitted from future studies. The rye flour that is sold in stores is often a mixture of different types," says Liza Rosén, a doctoral candidate in Applied Nutrition and Food Chemistry at the Lund University Faculty of Engineering, who has led the study. The research is part of the EU project "Healthgrain", in which researchers study how wholemeal products can be used to prevent diseases including type 2 diabetes and heart and vascular diseases.

According to Liza Rosén, if you want to optimize the health benefits, you should eat porridge or bread made from whole grain, where all the parts of the grain are included.

"This gives you all the benefits of rye. The bran includes many healthful fibers, vitamins, minerals, and antioxidants. This also helps give a feeling of satiety and helps lower blood sugar responses over the long term. On the other hand, we did not see such good results regarding blood sugar and insulin directly after the meal," she says.

In meal tests the researchers also found that individuals who ate boiled rye kernels for breakfast were fuller and ate significantly less for lunch, more precisely 16 percent less in energy intake, compared with those who ate bread made from white flour. They also found that both bread and hot cereal made with white rye and wholegrain rye are more filling than white wheat bread. The most effective form was rye porridges.

"It is probably the water in the porridge that increases the feeling of satiety. But the water has to be mixed into the product.  If you drink the same amount of water with rye bread, the results are not as good," she explains.

The original objective of Liza Rosén's research was to try to determine the reasons that wholegrain products are so beneficial, in that they have been shown to protect against cardiovascular diseases and certain types of cancer. There is also strong evidence that whole grains can prevent type 2 diabetes and insulin resistance.

"Since rye has been shown to yield low insulin responses, I started with that. A high insulin response can lead to insulin resistance in the body, that is, that the body has a hard time responding to insulin. Insulin resistance can result in high blood sugar, high blood pressure, and bad blood fats, which in turn increase the risk of age-related diabetes and cardiovascular diseases. Since I have found so much of interest, I haven't had yet time to look into barley, for instance, but perhaps in the future. On the other hand, several other researchers at Lund University have studied barley and its health benefits," says Liza Rosén.

Liza Rosén has not carried out any studies of how rye affects humans over the long term, but her colleague Ulrika Andersson did such a study on mice. For a half year a number of mice were fed wholegrain wheat or wholegrain rye, respectively. The results show that the mice that ate wheat gained significantly more weight than the mice on a rye diet.

"A possible explanation would be that wheat prompts a higher insulin response than rye, which means that the cells in the body can store more fat. The fact that rye contains more soluble fibers than wheat also plays a role, since they probably prevent the uptake of fat and other nutritional substances in the intestine."

There are only a few studies of how wholegrain forms of various cereal grains affect our health, so there is a great need for more detailed studies of the issue. Enhanced knowledge in this field creates a base for the development of a new generation of custom-designed wholegrain products that can counteract different types of diseases associated with our prosperity.

How the tests were done:

Study 1:

Twelve subjects ate breakfasts consisting of white wheat bread, porridge from wheat flour, white rye bread, wholegrain rye bread, wholegrain rye bread with lactic acid, hot cereal  porridge from wholegrain rye, and wheat bread with rye bran, all in rotation. The researchers monitored blood sugar, insulin, and satiety over the following three hours. The results for the various products were then compared with each other for each individual subject (that is, subject 1's response to wholegrain bread was compared with subject 1's response to wheat bread and subject 2's response with subject 2's responses, etc.).

Since the researchers found that the products that led to low insulin release provided greater satiety after three hours, they designed a second study to address the question: Can rye products that lead to low insulin response provide greater satiety and reduce the food intake in the following meal?

Study 2:

Ten subjects ate breakfasts consisting of white wheat bread, boiled wholegrain rye kernels (the whole grain), boiled whole wheat kernels, white rye bread, white rye bread baked with acid (corresponding to sourdough bread), wholegrain rye bread, and wholegrain rye bread baked with acid. The researchers monitored blood sugar, insulin, and satiety over the following 4.5 hours. For lunch, the subjects were allowed to eat as many meatballs and pasta as they wanted, until they felt full. Then the results were compared for the various products with each other and for each individual subject.

In an ongoing third study, the researchers are investigating different kinds of rye.