Whole wheat maintains more nutrients than refined flour during processing, research flags

02 Jul 2024 --- Scientists have uncovered new evidence supporting the addition of whole grains in a healthy diet, as is recommended in many dietary guidelines. According to their study, whole wheat retains more nutritional value during milling and baking than refined flour.

Major minerals were cut by nearly three-quarters in bread made with refined flour compared with whole wheat. Milling and baking also reduce the amount of vitamin E in refined and whole wheat products compared to raw wheat kernels. 

The research, presented at the ongoing annual meeting of the American Society for Nutrition, Nutrition 2024, traced how processing and backing influence nutrient composition at each step. 

“Tracking nutrient content from farm to table is key for appraising what agricultural products contribute to the diet,” says Dr. David Killilea, a researcher at the University of California, San Francisco, US. “Our experimental approach revealed that both milling and baking had significant impacts on multiple nutrient levels within wheat flour and bread.”

“Whole grains have an important role to play in the nutritional palette of the Western diet, and we strongly support the promotion of whole grain consumption,” he adds. “Processes that enrich the nutrient density of wheat-based foods should be encouraged, while processes that deplete nutrient density should be understood.”

Baking bread 
Researchers milled raw wheat kernels obtained from a single farm source to produce three different types of flour: whole wheat flour produced by stone milling, reconstituted whole wheat flour produced by roller milling and refined white flour created with roller milling, from which they removed bran and germ. 

Next, the research team used these three flours to prepare bread. 

At each processing step, the team assessed the levels of major minerals (calcium, magnesium, phosphorus, potassium), trace minerals (copper, iron, molybdenum, zinc), carotenoids (vitamin A-like compounds) and vitamin E. 

The researchers underscore the importance of a diet rich in whole grains with their high nutritional value.In both whole wheat flours, major mineral levels remained “virtually unchanged” from kernel to flour and bread, while levels of some trace minerals even increased during processing. 

However, major minerals were reduced by up to 72%, and trace minerals were reduced by up to 64% in refined flour and bread compared to wheat kernels. 

Moreover, vitamin E levels dropped significantly in each processing step, regardless of the type of flour used to bake the bread — bread contained less than one-fifth of the vitamin E levels of wheat kernels. Finished breads contained less than one-quarter of the carotenoid levels of wheat kernels. 

Dietary guidelines 
Although the Dietary Guidelines for Americans recommend that whole grains constitute at least half of the total grains, most people do not meet this recommendation. The researchers aim to underscore the importance of a diet rich in whole grains by revealing the substantial differences in nutritional value between more and less refined wheat products. 

The research team plans to determine how farming or processing practices could influence the nutrient density of wheat and wheat products. For example, they will focus on whether fermentation or other processes could help preserve the vitamin content of wheat content, as vitamin A and E deficiencies are a significant health concern in the US. 

Last month, Nutrition Insight reported on the controversy surrounding “golden rice,” a genetically modified variety aimed at addressing vitamin A deficiencies in low-income regions. Although independent scientific studies and assessment reviews support the product’s safety and efficiency, golden rice was recently banned in the Philippines, the first country to approve the commercial cultivation of the product in 2021. 

Meanwhile, South African researchers highlight the nutritional quality of climate-resilient sorghum bran, which contains higher levels of essential amino acids and minerals than whole grain or dehulled sorghum flour.