What Happens to Grains When They Are Refined?

January 6, 2026 •

4 min read

According to the Whole Grains Council, refining a grain removes about a quarter of its protein and half to two-thirds or more of its nutrients. This milling process strips the grain of its bran and germ, leaving only the starchy endosperm and fundamentally changing its nutritional profile and physical characteristics. The refining of grains, a process developed for shelf life and texture, has significant implications for public health.

Quick Summary

The refining process removes the fibrous bran and nutrient-rich germ from a grain, leaving only the carbohydrate-heavy endosperm. This industrial milling gives refined grains a finer texture and longer shelf life but dramatically reduces their nutritional value, including fiber, vitamins, and minerals. Some nutrients are added back in a process called enrichment, but the lost fiber is not restored.

Key Points

Nutrient Removal: The refining process strips grains of their bran (fiber and nutrients) and germ (vitamins, healthy fats), leaving only the starchy endosperm.
Enrichment vs. Restoration: Many refined grains are enriched with some B vitamins and iron after processing, but this does not fully restore the nutrients and, crucially, not the fiber lost during milling.
Blood Sugar Impact: Due to the removal of fiber, refined grains are digested rapidly, causing sharp spikes in blood sugar and insulin levels, unlike the steady release from whole grains.
Digestive Health: The lack of fiber in refined grains can negatively impact digestive health, whereas the fiber in whole grains supports regular bowel movements and a healthy gut microbiome.
Longer Shelf Life: The removal of the oil-rich germ, which can cause spoilage, is the primary reason that refined grains have a significantly longer shelf life than whole grains.
Different Health Outcomes: Health authorities recommend whole grains over refined grains, linking whole grain intake to a reduced risk of chronic diseases like heart disease and type 2 diabetes.

The Anatomy of a Whole Grain

To understand what happens during refining, one must first appreciate the composition of a whole grain. A whole grain kernel, such as wheat, oats, or rice, consists of three primary parts.

The Bran: This is the hard, protective outer layer of the kernel. It is a rich source of dietary fiber, B vitamins, antioxidants, and minerals like iron, copper, and zinc.
The Germ: This is the embryo of the grain, the part that has the potential to sprout into a new plant. It contains healthy fats, B vitamins, and protein.
The Endosperm: This is the largest part of the kernel and is the germ's food supply. It consists mostly of starchy carbohydrates, along with some protein and small amounts of B vitamins.

The Mechanics of the Refining Process

Refining is the industrial process of milling a grain to remove the bran and germ, leaving only the endosperm. This is typically done using modern roller mills that grind the grain and then sift out the undesirable components. The result is a smooth, fine flour or grain with a longer shelf life, as the oils in the germ that can cause spoilage are removed.

This process has been utilized since the 19th century, with the intention of making grains more palatable and durable for storage and transport. However, it came at a significant nutritional cost, leading to widespread deficiencies in some populations.

The Nutritional Consequences

When grains are refined, the most significant change is the loss of nutritional density. The majority of the fiber, vitamins, minerals, and antioxidants are stripped away along with the bran and germ. While some nutrients, like certain B vitamins (thiamin, riboflavin, niacin, and folic acid) and iron, are often added back in a process called 'enrichment,' the lost fiber is almost never replaced. This enrichment process, while beneficial for preventing specific deficiency diseases, does not restore the grain to its original nutritional state. The resulting refined grain is fundamentally a high-carbohydrate, low-fiber food.

The Impact on Digestion and Health

The shift in nutritional profile from whole to refined has profound effects on the body. Whole grains, with their high fiber content, are digested slowly, which helps regulate blood sugar levels and promotes a feeling of fullness. Refined grains, however, are digested much more quickly due to the lack of fiber. This leads to rapid spikes in blood sugar and insulin levels, which can contribute to weight gain and increase the risk of type 2 diabetes.

Health organizations, including the American Heart Association, recommend prioritizing whole grains over refined grains as part of a healthy diet. The fiber and plant compounds in whole grains have been linked to a reduced risk of heart disease, obesity, and other chronic conditions.

Comparison Table: Whole Grains vs. Refined Grains


Feature	Whole Grains	Refined Grains
Composition	Contains all three parts: bran, germ, and endosperm.	Contains only the starchy endosperm; bran and germ are removed.
Key Nutrients	Rich in fiber, B vitamins, antioxidants, magnesium, iron, zinc, protein, and healthy fats.	Lower in fiber, vitamins, minerals, and antioxidants; mainly starchy carbohydrates.
Enrichment	Not enriched, as nutrients are naturally present.	Often enriched with some B vitamins and iron to replace lost nutrients.
Fiber Content	High in both soluble and insoluble fiber.	Very low or no dietary fiber.
Digestion	Digested slowly due to high fiber content, leading to gradual blood sugar release.	Digested quickly, causing rapid spikes in blood sugar and insulin.
Health Impacts	Associated with lower risk of heart disease, type 2 diabetes, and obesity.	Associated with higher risk of weight gain, insulin resistance, and inflammation.
Shelf Life	Shorter shelf life due to oils in the germ.	Longer shelf life due to the removal of the perishable germ.
Texture	Often has a coarser, heartier texture.	Finer, smoother texture.

Conclusion

The refining process fundamentally alters a grain, transforming a nutritionally dense whole food into a processed product primarily composed of starchy carbohydrates. While this process offers advantages like longer shelf life and a finer texture, the trade-off is the significant loss of essential fiber, vitamins, and minerals. Though enrichment adds back a few of the lost nutrients, it does not compensate for the dietary fiber that plays a crucial role in regulating blood sugar and promoting digestive health. For optimal health, dietary guidelines consistently recommend choosing whole grains over their refined counterparts to benefit from their complete nutritional profile and support long-term well-being. Ultimately, understanding what happens to grains when they are refined allows for more informed and healthful food choices. The Whole Grains Council offers valuable information on identifying and incorporating whole grains into your diet.

Frequently Asked Questions

During the refining process, the bran and the germ are removed from the grain kernel. The bran is the fibrous outer layer, and the germ is the nutrient-dense embryo of the grain.

Refined grains are less nutritious because the bran and germ, which contain most of the fiber, vitamins, minerals, and antioxidants, are removed during the milling process, leaving only the starchy endosperm.

Enriched means that some of the B vitamins and iron that were lost during the refining process have been added back to the grain. However, the lost fiber is not typically restored.

Refined grains, with their low fiber content, are digested quickly, which can cause rapid spikes in blood sugar and insulin levels. This contrasts with whole grains, which provide a more gradual release of sugar into the bloodstream.

Refined grains have a longer shelf life because the germ is removed. The germ contains healthy fats that can go rancid and cause spoilage over time.

In some cases, such as for individuals with certain digestive issues like inflammatory bowel disease (IBD) or for those following a low-residue diet, a doctor may recommend refined grains because their low fiber content is easier to digest.

No, brown bread is not always whole grain. Some food processors add coloring, like caramel, to refined flour to give it a brown appearance. To be sure, you should check the ingredients list for 'whole' in the name or look for the Whole Grain Stamp.