Sugar is a carbohydrate, so the real question is whether starchy carbs like bread, rice, and pasta are worse for blood sugar than the sweet stuff in a candy bar. The answer surprises most people: many common starches spike blood sugar just as fast as, or faster than, table sugar. A serving of white rice, for example, has almost the same blood sugar effect as eating pure table sugar. For someone with diabetes, the total amount of carbohydrate you eat matters more than whether those carbs come from sugar or starch.
Why Starch Can Spike Blood Sugar as Much as Sugar
Table sugar (sucrose) is a combination of glucose and fructose. Starchy foods like white bread, white rice, and crackers are long chains of glucose molecules. Your digestive system breaks those chains apart quickly, flooding your bloodstream with glucose in a pattern that looks remarkably similar to eating sugar straight.
The glycemic index, which rates how fast a food raises blood sugar compared to pure glucose, makes this clear. White bread, rice cakes, bagels, and most packaged breakfast cereals all score 70 or above on the scale, putting them in the highest category. Table sugar actually scores lower, around 65, because the fructose half gets routed to the liver instead of hitting the bloodstream directly. So a plain bagel can raise your blood sugar faster than a spoonful of sugar.
Maltodextrin, a processed starch found in many packaged foods (including some marketed as healthy or diabetic-friendly), is digested and absorbed at the same rate as pure glucose. It triggers a nearly identical insulin response. If you see maltodextrin on a label, treat it the same as sugar when counting carbs.
Total Carbs Matter More Than Carb Type
Research on people with type 2 diabetes who weren’t taking medication found that total daily carbohydrate intake correlated with HbA1c, the measure of long-term blood sugar control. The more total grams of carbohydrate people ate per day, the higher their HbA1c tended to be. This held true for men and women, though the specific food sources that drove the correlation varied. In men, carbs from noodles and sugary drinks had the strongest link. In women, rice was the biggest contributor.
This means fixating on “sugar-free” labels while eating large portions of rice, bread, or pasta can be counterproductive. Your body converts all digestible carbohydrates into glucose eventually. Whether the carbs came from a cookie or a bowl of white rice, a large enough portion will push blood sugar up.
Not All Starches Are Created Equal
Starch molecules come in two main forms. One type is a straight chain that your body digests slowly. The other is a branched structure that enzymes can attack from many angles at once, breaking it down rapidly. The ratio between these two forms determines how fast a starchy food hits your bloodstream.
In a controlled study, meals made with the slow-digesting straight-chain starch produced significantly lower glucose and insulin responses than meals made with the fast-digesting branched starch. After five weeks on each diet, the difference was even more pronounced for insulin levels. This is why foods like lentils, barley, and certain long-grain rices (which are higher in the slow-digesting form) behave very differently than white bread or instant mashed potatoes, even though they’re all “carbs.”
High amylose rice, the slow-digesting variety, has a glycemic index of 38. Standard low amylose rice scores 57. That’s a meaningful difference from the same basic food.
Fructose Presents a Different Problem
The fructose half of sugar doesn’t raise blood glucose directly, which is why sugar’s glycemic index is lower than white bread’s. But this doesn’t make fructose harmless. It creates a separate set of problems, particularly for people already dealing with insulin resistance.
Fructose is processed almost entirely by the liver. When large amounts arrive at once (from sugary drinks, fruit juice concentrates, or foods with added sugar), the liver converts much of it into fat. Unlike glucose, which stimulates both fat production and fat removal to maintain balance, fructose stimulates fat production while impairing removal. This drives up triglycerides and contributes to fatty liver, both of which worsen insulin resistance over time.
In one comparison, a diet with 20% of calories from fructose raised fasting LDL cholesterol by 11% compared to a starch-based diet. Animal studies using euglycemic clamp testing, the gold standard for measuring insulin sensitivity, showed clear fructose-induced insulin resistance that didn’t occur with equivalent glucose feeding. A diet high in sucrose also produced significantly higher fasting insulin and blood glucose levels compared to a starch-based diet, with even more pronounced effects in people classified as carbohydrate-sensitive.
So while starchy carbs may spike blood glucose faster in the short term, the sugar in sweetened foods and drinks does unique damage to metabolic health over time. Both matter, through different mechanisms.
Why Fiber Changes the Equation
Fiber is technically a carbohydrate, but your body can’t break it down into glucose. More importantly, fiber slows the digestion and absorption of the carbohydrates it’s paired with. This is why a bowl of steel-cut oats behaves very differently in your body than a bowl of instant oatmeal, even though both are “oats.”
The blood sugar reductions from fiber are significant and well-documented. Adding a soluble fiber called guar gum to a meal reduced the glucose peak by 41% to 68%, depending on the dose. A different type of fiber (resistant maltodextrin) showed a consistent pattern across dozens of studies: at least a 20% reduction in blood sugar response for every 10 grams consumed. Even modest amounts of fiber in bread made from wheat bran extract significantly lowered blood glucose peaks.
This is the practical takeaway for diabetes management. The distinction that matters most isn’t “carbs versus sugar” but rather “refined versus intact.” A slice of white bread and a serving of cooked lentils are both carbohydrates. But the lentils come packaged with fiber, have a slower-digesting starch structure, and produce a much gentler blood sugar curve. The white bread, stripped of its fiber and made from fast-digesting starch, behaves more like sugar than the sugar itself does.
A Practical Framework for Choosing Carbs
If you have diabetes, thinking in terms of “carbs versus sugar” can actually lead you astray. Here’s what the evidence points to instead:
- Watch total carb portions first. Total daily carbohydrate intake has the strongest link to long-term blood sugar control, regardless of whether those carbs come from sugar or starch.
- Choose intact, fiber-rich sources. Beans, lentils, barley, non-starchy vegetables, and whole intact grains (not “whole grain” flour products) produce far gentler blood sugar responses than refined grains or added sugars.
- Treat refined starches like sugar. White bread, white rice, crackers, and most breakfast cereals spike blood sugar as fast as or faster than table sugar. “Sugar-free” products made with refined flour or maltodextrin are not meaningfully better.
- Limit liquid sugars specifically. Sugary drinks deliver large doses of fructose to the liver rapidly, worsening insulin resistance and triglycerides through a pathway that starches don’t trigger as strongly.
The bottom line is that refined carbs and sugar are essentially two faces of the same problem. Neither is categorically “worse.” Refined starches often do more immediate damage to blood glucose readings, while added sugars (especially fructose-heavy sources) do more hidden damage to insulin sensitivity and liver fat. For someone managing diabetes, reducing both while shifting toward high-fiber, slow-digesting carbohydrate sources is what actually moves the needle.