Obesity and metabolic disease are complex conditions, driven by a variety of factors, including genetics, environment, diet and lifestyle. But after poring over decades of research and interviewing leading nutrition researchers, Dr. Kessler found that one thing most successful diets have in common is that they limit highly processed carbs.
Yet foods that contain these fast carbs have become a mainstay for many people. According to the federal government, grain-based desserts such as cookies, doughnuts and granola bars are the largest source of calories in the American diet, followed by breads, sugary drinks, pizza, pasta dishes and other processed foods. About 60 to 70 percent of processed foods contain refined wheat, corn, tapioca, rice, potatoes and other fast carbs as their primary ingredient.
Humans have been processing foods in various ways for thousands of years, whether cooking, boiling, grinding or milling them. But Dr. Kessler argues that the industrial processing of carbs that occurs today has a far more pronounced effect on food than the techniques used by our ancestors.
“If cooking and milling were early forms of processing,” he writes, “today’s food manufacturing strategies are more aptly called ultraprocessing.”
Most of the grains that are used in foods like breakfast cereals, corn chips and crackers are milled by high-speed steel rollers. Then they are further pulverized through a variety of high-pressure techniques. One of these is extrusion cooking, a thermal and mechanical process that dramatically alters the chemical structures of grains, breaking down their long chains of glucose into smaller starch molecules that can be rapidly digested.
“The physical properties of the original starch molecule are no longer the same,” Dr. Kessler writes. “The granule structure has been destroyed, the glucose polymer chains have been reduced in size, and their surface area has expanded, which increases how fast we absorb these foods from our digestive tract into our bloodstream.”
Our intestines average about 25 feet in length, an evolutionary adaptation that allows us to gradually extract glucose from relatively intact starches as they move through our systems. But processes like extrusion essentially predigest starches for us: They arrive in our stomachs as a soft, porous paste, and the glucose they contain is largely absorbed in the first part of the small intestine beyond the stomach, the duodenum, circumventing the need to travel through the whole digestive tract.