Human digestion seems to be a pretty simple matter of intake and output, but there are many unsolved mysteries surrounding this vital system. How does our body break down, transport and absorb food?

To help answer some of the questions and eventually enable people to make more healthful food-related decisions, a UC Davis researcher has developed a tabletop “digestion machine.”

“The body is a food-processing plant with a digestive system we know very little about,” said the digestion machine’s inventor, Gail Bornhorst, an engineer and assistant professor in the departments of Biological and Agricultural Engineering and Food Science and Technology.

Called the Human Gastric Simulator, the machine is composed of a network of gears, rollers, plastic bags and chains within a metal framework. The novel contraption was designed and built to mimic the human digestive system. Information gathered from studies using the machine may one day give people a better idea of when to eat, what to eat and how to prepare food to meet their own personal nutritional needs.

“We know a lot about the makeup of food as it goes in and comes out, but not much about what happens in between,” Bornhorst said. “Our goal is to quantitatively describe food breakdown, transport and absorption to optimize food quality and functionality.”

She noted that as human beings, we want something from our food. We may eat to feel full and energized or we may want certain nutrients or extra protein in our meals. We can evaluate the properties of the food we consume — or trust the marketing and ingredients listed on a label — but in many cases it’s unclear how our bodies absorb the nutrients, additives and molecules we ingest.

“We know how a tomato-processing plant works because we can stick sensors inside the tanks,” Bornhorst said. “It’s not so easy with human digestion.”

Researchers are starting to find noninvasive ways to study digestion in live animals and humans using techniques such as magnetic resonance imaging, but those methods are limited, costly and ethically controversial. The new digestion machine developed by Bornhorst and her research team provides an alternative research method by mimicking both the biochemical and physical conditions of a human digestive tract.

“We can add acids and enzymes to the ‘stomach’ to simulate gastrointestinal fluids,” Bornhorst said, pointing to a liquid-filled, plastic bag at the center of the device. With the flip of a switch, she turned on a network of slow-moving cranks and plastic rollers that compress the cavity of the bag, mimicking stomach contractions.

Her lab is testing a variety of fruits, vegetables and beverages to see how they move through the system. The researchers also are looking at how different cooking and processing methods such as boiling, steaming and frying influence the breakdown and transport of food.

“Turns out, how you prepare your food influences digestion quite a bit,” Bornhorst said. “We’re even seeing digestive differences depending on which variety of raw apple you eat.”

At this point, she said, it’s too early for any sweeping conclusions, except maybe that digestion is very complex.

“There are a lot of moving parts and many variables, even person to person,” she said.  “We’re working to quantify the fundamental transport processes to better understand things like nutrient release and absorption rates.”

Eventually the machine should provide the researchers with a more holistic understanding of human digestion, and that, in turn, should help people make more informed decisions about how to meet their nutritional needs.

Diane Nelson is a senior writer in the College of Agricultural and Environmental Sciences.