The Nutrition Facts panel focuses our attention on calories, fat, sugar, and salt. It lists total carbohydrates, but does not distinguish between the fast and the slow carb varieties. Yet the processed starch of fast carbs represents a staggering percentage of the calories we consume. Think of hamburger rolls, pizza dough, and fries. The average American eats more than 1,000 calories of rapidly digestible starches and sugars every day, and gets 500 more from the fats and oils added to many of these products. Starch serves as the carrier for much of the fat, sugar, and salt that we ingest, and like sugar, it is converted into rapidly absorbable glucose.

All of this undermines what should have been an American success story. We became an agricultural powerhouse because of the nation’s abundance of fertile grasslands, ideal for growing grain, and the industrial infrastructure that refines that grain into starch. But the processed carbs that became our main food source have also proved to be a missing link between obesity and metabolic dysfunction. That story has largely gone untold. Despite all the research on nutrition and disease in recent years, the effects of inundating our bodies with a constant stream of rapidly absorbable glucose—a poison hiding in plain sight—has not been well examined.

Modern processing techniques involve intense heat and mechanical forces that destroy the structure of food. In addition, food manufacturers add fat and salt to highly processed carbs to increase their palatability, making them much softer and easier to chew and swallow. We thus eat more and we eat it faster. Because the nutrients never reach the lower part of the gastrointestinal tract, hormones that should trigger signals of fullness don’t get stimulated. (By contrast, less-processed foods retain their tight structure so that enzymes don’t break them down completely; we can still digest the food, but may not absorb all of its calories.)

Fast carbs elevate blood glucose, and with it, insulin levels. When this happens repeatedly, especially in people who are overweight, metabolic pathways can become dysfunctional: Insulin stops working effectively, leading to insulin resistance, and eventually, diabetes and other disorders. Our bodies become intolerant to fast carbs, and by continuing to eat them, we further accelerate metabolic dysfunction.

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The dangers of processed carbs are amplified in an environment of positive energy balance—that is, a world in which bodies take in more calories than they burn. Historically, humans had to work hard to find food and were lucky to get enough calories to match their energy expenditures. When we burned at least as much as we consumed, processed carbs didn’t present the same problems—especially when those carbs weren’t as highly processed, because we didn’t have industrial techniques to shatter the food matrix so completely. But today, when many of us struggle with weight and confront disorders like prediabetes or worse, processed carbs are a disaster. It is shocking, but perhaps no surprise, that only about 12.2 percent of Americans are cardio-metabolically healthy, their blood pressure, lipid levels, blood glucose, and weight falling within current guidelines, a repercussion of these changes.