Grains are rich sources of complex carbohydrates (that supply glucose, the main fuel needed by the brain and body for energy) and contain some plant protein as well. They’re also good sources of vitamins and minerals such as folate, thiamin, niacin, iron, and magnesium.
Whole grains are foods that include all the essential part of the entire grain seed or kernel (including the nutrients and other components found in those parts). A whole grain includes three key components: the bran (outer layer), the germ (innermost part), and the endosperm (middle layer).
Some commonly consumed whole grain foods include whole wheat bread, oatmeal, whole wheat pasta, brown rice, whole wheat crackers, and popcorn. Whole grains are often good sources of dietary fiber (even though amounts vary from about ½ gram to 4 grams per serving). They also contain the B vitamins folate, thiamin, riboflavin, and niacin, as well as the minerals iron, magnesium, and selenium.
Refined grains are made when whole grains are milled into four to make breads, pasta, cereals, and other foods. Unfortunately, milling removes two key components of whole grains – the bran and germ. That means the end product does not have many healthful nutrients such as fiber, vitamins, minerals, and phytochemicals that are specifically found in those parts of the whole grain. Only the endosperm, which contains some protein, vitamins, and minerals, is unaffected by milling and is intact on the final product produced.
Fortunately, many refined grains are enriched with several B vitamins and iron. Despite this, refined grains are usually not as nutritious as whole grains because they are missing other nutrients, especially minerals, phytochemicals, and fiber.
Refined grains often have less fiber and are digested and absorbed more quickly than whole grains and therefore tend to be less filling. Many refined grains also have a high glycemic index (GI). Research suggests that people who consume too many high-GI foods have more than double the risk for developing diabetes compared with those who consume fewer high-GI foods. High-GI foods enter the bloodstream quickly, which raises blood sugar levels. That then triggers the pancreas to release the hormone insulin into the bloodstream, which lowers blood sugar to more normal levels. Too many, or large portions of, high-GI foods can overwork the pancreas, which keeps releasing more and more insulin. To much insulin in the blood can contribute to high blood cholesterol, high blood triglycerides, low HDL or (“good” cholesterol), and increased blood clotting.
A recent study also found people who consumed a lot of refined carbohydrates (refined grains as well as added sugars) doubled their risk for heart disease.
Many of the starchy, baked, snack-type grains we commonly consume are made primarily or solely of refined grains. Some common refined grains include white breads; rolls; flour tortillas; white rice; pasta; crackers; and snack foods such as pretzels, potato chips, cakes and cookies.
A cone-ounce equivalent serving of grains equals approximately:
• 1 cup read-to-eat cereal flakes or puffs
• ½ to ¼ cup ready-to-eat cereal nuggets
• ½ cup cooked cereal
• 1 ounce dry or ½ cup cooked pasta or rice
• 1 slice of bread
• 1 ounce of crackers
The bran is the protective multilayered outermost component of a whole-grain seed or kernel. It contains antioxidants; B vitamins; the minerals iron, zinc, copper, and magnesium; fiber; and phytochemicals.
The endosperm is the largest part of the whole grain seed or kernel. It contains carbohydrates (specifically starches), protein, and small amounts of vitamins and minerals.
Enriched grains contain many of the nutrients lost during processing. The B vitamins thiamin, riboflavin, and niacin and the mineral iron are added back after whole grains are milled to produce refined flour.
Glycemic index (GI) measures how much a food or beverage raises blood sugar or blood glucose levels. Foods or beverages that have high GI values raise blood sugar more rapidly (and higher) than those with lower GI values.