Refining Flour Strips Away Essential Nutrients, Says Study

A new study illuminates the nutrients lost during flour refining and emphasizes the benefits of whole wheat.

The study, presented at NUTRITION 2024, the flagship annual meeting of the American Society for Nutrition, is among the first to identify how processing and baking influence nutrient composition at each step.

Researchers obtained raw wheat kernels from a single farm. The kernels were milled to produce three different types of flour, which were used to prepare bread.


At each step, researchers assessed the levels of major minerals, such as calcium, magnesium, phosphorus, and potassium, as well as trace minerals like copper, iron, molybdenum, and zinc. They also looked at the content of vitamin E and carotenoids.

The three flour types included intact whole wheat flour (produced by stone milling), reconstituted whole wheat flour (produced by roller milling), and refined white flour (produced by roller milling with bran and germ removed).

Refined flour and bread contained up to 72% and 64% less major minerals and trace minerals compared with wheat kernels, respectively.

The levels of major minerals remained practically unchanged in the two types of whole wheat flour while processing even increased the content of some trace minerals.

Vitamin E levels decreased substantially with each processing step, regardless of the type of flour. Breads made with all flour types contained less than one-fifth the amount of vitamin E as wheat kernels.

Baking flour into bread also cut the levels of carotenoids: all bread contained less than one-quarter the amount of carotenoids as wheat kernels.

David Killilea, Ph.D., a researcher at the University of California San Francisco, said that tracking nutrient composition from farm to table is key for evaluating what agricultural products actually contribute to the diet.

“Our experimental approach revealed that both milling and baking had significant impacts on multiple nutrient levels within wheat flour and bread,” Killilea said in a statement.


An essential part of a healthy diet

In a healthy dietary pattern, at least half of total grains should be whole grains, according to the Dietary Guidelines for Americans. A food is 100% whole-grain food if the only grains it contains are whole grains.

However, 98% of Americans fall below recommendations for whole grains, and 74% exceed limits for refined grains. High consumption of refined grains is associated with an increased risk of major cardiovascular disease, stroke, and early death.

In the American diet, nearly half of the refined grains consumed come from mixed dishes such as sandwiches, burgers, tacos, and pizza.

Individuals can increase their whole-grain intake and lower their refined grain intake by shifting to whole-grain versions of commonly consumed foods, such as from white to 100% whole-wheat bread and white to brown rice.

Moreover, shifting to more nutrient-dense forms of grains, such as ready-to-eat breakfast cereals with less sugar, can help meet healthy dietary patterns.

The new study reveals how refining flour significantly cuts the levels of major minerals and trace minerals, making refined grains a less nutritious food choice.


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