Refined grains drive insulin resistance and type 2 diabetes. Stripped of bran and germ, flour digests into fast starch. That spikes blood sugar and forces the pancreas to pump out insulin. It also fuels overeating and stokes inflammation.
Flour is hard to avoid at meal times. Breakfast is mostly toast, bagels, cereal, and pancakes. A handy lunch is sandwiches, wraps, pasta or pizza. Dinner might bring its own temptations too. As a result, the average American now eats 10 servings of refined grains each day. What do these refined grains do to your health? Does eating refined grains set you up for type 2 diabetes? In this article, we look at factors that could put you at risk.
- What Is the Difference Between Whole Grains and Refined Grains?
While whole grains are very high in dietary fiber, refined grains are much lower in fiber and micronutrients.
Whole grains consist of three main parts:
- Bran: The hard outer layer, containing fiber and minerals.
- Germ: The nutrient-rich core, containing carbs, fat, protein, vitamins, minerals, antioxidants and plant compounds.
- Endosperm: The middle layer, containing mostly carbs and small amounts of protein.
The bran and germ are the most nutritious parts of whole grains. They hold large amounts of many nutrients, such as fiber, B vitamins, iron, magnesium, phosphorus, manganese, and selenium.
Refining removes the bran and germ, along with all the nutrients they hold. Taking out those nutrients has effects. On the upside, it makes things like bread doughy and spongy — textures we like and have come to crave. On the downside, the food’s nutritional value is severely reduced. These stripped grain products actually drain our body’s stores of important vitamins and minerals.
The nutrient content of refined flour depends on the ‘extraction rate’ (the share of the grain kept after milling). Refined flour made in Australia is milled to an extraction rate of 78-80%. That gives it more nutrients (before fortification) than flour from countries that use a lower extraction rate (e.g. 73-75% in the USA).
This leaves almost no fiber, vitamins or minerals in the refined grains. What’s left is fast-digesting starch with small amounts of protein.
- Why are refined grains bad for you?
- Blood sugar spikes: Because flour is easy to digest, it makes our blood sugar spike, which could lead to a rise in insulin. The pancreas has to crank out a lot of insulin to process the glucose in flour-rich foods. That can set the body up for insulin resistance, diabetes, and bodywide inflammation. Refined grains have a higher glycemic index, which measures how quickly the body turns food into fuel, or glucose. A carbohydrate in wheat, called amylopectin A, turns into blood sugar more easily than most other carbohydrates. Two slices of bread made with whole-wheat flour could raise blood sugar higher than six teaspoons of table sugar. They could also raise it higher than many candy bars.
- Overeating and Obesity: Obesity is the leading factor in insulin resistance, type 2 diabetes, and other chronic diseases. Eating too many refined carbs may be one of the main culprits. They are low in fiber and digest quickly, so eating them can cause major swings in blood sugar levels. This can contribute to overeating.
- As we said above, foods high on the glycemic index keep you full only a short time, about one hour. Foods low on the glycemic index keep you full longer, about two to three hours. Blood sugar levels drop about an hour or two after a meal high in refined carbs. This drives hunger. It also fires up parts of the brain associated with reward and craving.
- These signals make you crave more food, and they are known to cause overeating. This constant eating leads to obesity, a pre-diabetic state, and finally diabetes.
- Slower Metabolism: Research shows that the body may shift nutrients into fat storage and away from muscle burning when it gets high-glycemic-index foods. In 2004, Ludwig and his colleagues at Harvard ran a study, published in the journal Lancet. They fed rats diets with identical nutrients, except for the type of starch. By the end of the study, rats in both groups weighed roughly the same. But those eating a high-glycemic diet had 71 percent more fat than the low-glycemic-index group.
- Inflammation: A diet high in grains stokes inflammation. When blood sugar spikes, glucose builds up in the blood. As glucose drifts in the blood, it could attach itself to nearby proteins. The result is a chemical reaction called glycation. Glycation is a pro-inflammatory process that plays a role in a host of inflammatory diseases — everything from Type 2 diabetes to arthritis to heart disease.
- GI Disorders: Studies show that the lectins in grains inflame the lining of the gut and create cracks between cells. Also, when whole-kernel grains are refined, 80 percent of the fiber is lost, and gut health suffers. Without the fiber, these grains become fast-release carbs, which is bad for the gut. Fiber helps sweep debris out of the gut. It supports the body’s vital elimination and detox processes. Those processes also help keep high cholesterol and inflammation in check.
- Food Allergies/Intolerances: Wheat, in particular, is one of the biggest food triggers of allergies and intolerances. The exact reason is unclear, but many experts blame the higher gluten content of modern wheat. Gluten is a type of protein found in many grains, including wheat. It gives dough its stretch, trapping air bubbles and creating a soft texture. Because soft is seen as desirable, wheat today is bred to have more gluten than ever before.
- Acid-Alkaline Imbalance: The body has a detailed system of checks and balances to keep its pH level at a steady 7.4. A diet high in acidic foods, such as grains, forces the body to pull calcium from the bones to keep things balanced. Researchers looked at how the diets of more than 500 women affected their bone density. They found that a diet high in refined grains, among other nutrient-poor foods, was linked to bone loss. A highly acidic diet also wears away at our cells’ health and our immunity in ways that can leave us open to chronic disease. Grains are the only plant foods that create acidic byproducts. Wheat, in particular, is among the most potent sources of sulfuric acid. Sulfuric acid is a powerful substance that quickly overwhelms the neutralizing effects of alkaline bases.
- What are the healthiest grains to eat?
Whole grains keep more fiber, vitamins and minerals than refined grains. But they are still starch, and wheat, barley and rye still carry gluten and gliadin. In chronic pain, gluten and gliadin drive a leaky gut and autoimmune trouble. Here are a few steps to cut back on grains:
- While baking, replace the flour with nut or seed meals.
- Don’t overdose on gluten-free foods.
- Try going flour-free.
- Consider a grain sabbatical.
- Do refined grains cause insulin resistance and type 2 diabetes?
When ground into flours, most grains act like sugar in the body. They trigger weight gain, inflammation, and blood-sugar imbalances. Studies show that high intake of refined carbs is linked with insulin resistance and high blood sugar levels. These are some of the main symptoms of type 2 diabetes.
Refined carbs also raise blood triglyceride (blood fat) levels. This is a risk factor for both heart disease and type 2 diabetes. So we recommend no refined grains for our patients.
Frequently asked questions
What are examples of refined grains?
Anything made from refined flour. That covers most of the American menu: toast, bagels, cereal and pancakes at breakfast, then sandwiches, wraps, pasta and pizza later in the day. Refining strips out the bran and germ and leaves the starchy middle layer. The average American now eats 10 servings of refined grains every day.
What are the health effects of refined grains?
Refined flour digests fast, so blood sugar spikes and the pancreas has to pump out extra insulin. That sets the body up for insulin resistance and type 2 diabetes. The drop in blood sugar an hour or two later drives hunger and overeating. Refined grains also stoke inflammation through glycation. They strip away the fiber your gut needs and raise blood triglycerides.
Which grains are not refined?
Whole-kernel grains that keep all three parts: the bran, the germ and the endosperm. Sprouted grains and truly whole-grain flours also count. Whole grains are still starch, and wheat, barley and rye still carry gluten, so we do not build meals around them. When you bake, replace the flour with nut or seed meals. Or go flour-free and take a grain sabbatical.
Related reading
References
- Grains & legumes Nutrition Council (2019): Refined grains. Retrieved from https://www.glnc.org.au/grains/grains-and-nutrition/refined-grains/
- NCBI (2002): Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/11976158
- Popsugar (2019): 4 Reasons to Eat Whole Grains Instead of Refined. Retrieved from https://www.popsugar.com/fitness/Why-You-Should-Eat-Whole-Grains-Instead-Refined-18361716
- Healthline (2017): Why Refined Carbs Are Bad For You. Retrieved from https://www.healthline.com/nutrition/why-refined-carbs-are-bad
- Experience Life (2019): The Truth about Refined Grains. Retrieved from https://experiencelife.com/article/the-truth-about-refined-grains/
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
