Worldwide more than 300 million people live with obesity and 460 million people live with type 2 diabetes, creating a significant global public health burden. A key contributor to weight gain and the metabolic dysfunction that drives type 2 diabetes is dietary starch, a major energy source for populations around the world. Findings of a recent study describe the relationship between starch structure and post-meal blood sugar response.

Starch is a carbohydrate derived from grains, beans, and some vegetables. It is composed of chains of glucose molecules that can be arranged in straight structures (called amylose) or branched structures (called amylopectin). High-amylose starches, which are found in foods like beans, Basmati rice, and green bananas, form very tight structures that slow digestion and are less likely to cause blood glucose spikes. High-amylopectin starches, which are found in foods like white bread, sticky rice, and pastries, are more rapidly absorbed and are far more likely to cause blood glucose spikes.

Adding water to starches and heating them, a process known as gelatinization, increases their digestibility and capacity to increase blood glucose, while heating and then cooling starches (e.g., cooking potatoes and eating them in a cold salad) can create beneficial starches (called retrograde starches) that are resistant to digestion and do not increase blood sugar. Evidence suggests that consuming resistant starches improves insulin sensitivity in men with overweight or obesity. Mechanically processing starches (e.g., milling flour or blending fruits) also increases the digestibility and capacity to increase blood glucose.

The authors of the current study conducted a systematic review and meta-analysis in which they searched the literature for studies testing starches and their effects on post-meal metabolism, collected studies based on a set of criteria meant to select for high-quality design, and then combined the data for analysis. The authors found 45 studies that met the selection criteria for this review. These studies investigated starch characteristics, such as gelatinization, retrogradation, protein content, and particle size, and metabolic responses to starch intake, such as blood glucose and insulin levels and appetite suppression.

Analysis of the 45 studies revealed significant reductions in post-meal blood glucose and insulin levels when the starch consumed had a high amylose content, was less-gelatinized, contained retrograded starch, or contained intact and large particles. Investigators used a variety of starch foods in these studies including some grains with a naturally high or low amylose to amylopectin ratio. In other trials, investigators used blends of specific flours to achieve their desired amylose to amylopectin ratio. Less gelatinized starches included uncooked rice compared to cooked rice. Retrograded starches included reheated rice compared to freshly cooked rice. And starches with large and intact particles included whole peas compared to pea flour. The authors did not have sufficient evidence to report a relationship between starch type and appetite suppression.

The authors concluded that manipulating the structure of starches alters the body’s metabolic response to starchy foods. Consuming starches from raw foods, which have larger, more intact, and less gelatinized particles, or from heated and cooled grains or vegetables with retrograded starches may reduce the risk of type 2 diabetes.

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