A correction to an earlier version of this article has been appended to the end of the article.

On a recent summer afternoon, Randy and Vera Tom prepared a stir-fried lunch in their Redwood City home with their “sous chef,” a 17-year-old Bichon Frise named Munchies, afoot.

Randy, 70, recently overhauled his lifestyle after the couple participated in a Stanford Medicine study tracking their metabolic responses to carbohydrates in real time with a continuous glucose monitoring device.

The recently published research tracked the glucose levels in the blood of 55 study subjects as they consumed precooked meals starring different carbohydrates such as grapes, jasmine rice, potatoes, pasta and bread. It was led by genetic deep data specialist Mike Snyder, metabolic expert Tracey McLaughin and research dietician Dalia Perelman at Stanford.

The results could lead to better prevention, diagnoses and treatment of prediabetes, diabetes and other metabolic diseases that lower quality of life and raise health care costs.

According to the Centers for Disease Control and Prevention, 38.4 million people, or 11.6% of the U.S. population, had diabetes in 2024.

Most common is Type 2 diabetes, which occurs when the body develops resistance to insulin because of diet, lifestyle, weight and family history. Type 1 diabetes is an autoimmune disease attacking cells of the pancreas, disabling the body’s production of insulin, the hormone that orchestrates the body’s food-processing functions. Both types of diabetes are life-threatening without intervention.

According to the CDC, more than a third of the 250 million people 18 or older in the U.S. and almost half of the 60 million who are 65 or older are prediabetic — the vast majority unknowingly.

“How would you know, if you can only know with a test that you get only if there seems to be a problem?” asked Randy, cleaver in hand, chopping neatly organized piles of lean pork and technicolor-green bok choy.

The opportunity to access more personalized health information while contributing to science attracted the Toms to Stanford’s genomics studies about a decade ago. They’ve been in more than five long-term studies since — the latest was the first involving food.

When the research team asked Randy what he ate over Christmas after seeing spikes in his blood sugar data, the culprit was tamales. Now, he enjoys just one of the corn-based treats per sitting.

For Snyder, the advancement of physiologically specific care has been personal. From 2009 to 2011, he and Stanford profiled his own descent from prediabetes into type 2 diabetes — the first time the phenomenon was documented at the molecular level.

Snyder, who is svelte and active, said, “When I first became diabetic, everybody looked at me and said, ‘No way, it’s gonna go away.’”

But the proof was in his integrative Personal “Omics” Profile, or iPOP, an unprecedented analysis of billions of individual bits of molecular genetic data collected by powerful cutting-edge technology.

This level of analysis allows researchers to understand people by metabolic subtype and tailor treatment to match.

Right now, doctors begin to classify metabolic shifts or prediabetes when glucose levels in the blood exceed 5.7%, with no information as to why the abnormality exists.

But there are four different pathways to metabolic disease — two where the body doesn’t produce enough insulin and two where the body doesn’t respond properly to insulin.

In the study, McLaughlin and Snyder looked for soft slopes in blood sugar. Jagged peaks are generally normal responses to food or sugar.

Everyone’s blood sugar spikes in response to grapes and rice. But the scientists found that people with metabolic problems spiked higher and for longer to potato starch than people who lacked problems. The “potato-to-grape” reaction ratio correlated with different underlying metabolic dysfunctions.

These differences call for precision medicine and targeted preventative measures. Some people might need weight loss. Others might need exercise. Yet others may need sleep — something that lowers blood glucose levels across the board.

“If we understand where the problem lies, we can treat it more effectively,” Perelman said.

The researchers are looking for markers in cells that can identify these problems more easily through simple blood tests.

In the meantime, continuous glucose monitoring offers actionable information for people who want to be proactive about their metabolic health.

“You see what spikes you, you see what doesn’t spike you, so you eat what doesn’t spike you,” Snyder said.

After the study wrapped, the Toms obtained their own monitoring devices. Vera, 71, reacted moderately to her data; Randy took things further.

He avoided foods that caused sustained spikes in his blood sugar and joined a master’s swimming team. The retiree and part-time model dropped 25 extra pounds, shed numbers from his high cholesterol count and reversed his prediabetic condition.

“I don’t think people know that you can reverse it,” he said. “It’s just hard to do. You don’t just take a pill.”

Last fall, continuous glucose monitors became available over the counter. A drawback is the $80 monthly cost because insurance only covers the devices for diabetics.

Snyder, who wears multiple devices tracking his body’s functions and removes them only before getting weighed, thinks everyone should try one.

Perelman said the monitors are not a replacement for clinical consultation. McLaughlin added that the devices can yield false metrics in certain situations.

The next phase of the research will test different foods and “mitigators” — proteins or fats that can lower blood sugar fluctuations when consumed with carbohydrates. Toasted bread, for example, is easier on the system for some people when eaten with meat or a fat source like heavy cream. Mitigators don’t work as well for people with metabolic disorders — another crumb for research. Cornflakes and milk? Bad for nearly everyone.

This time, study participants will receive interventions, from medicine to personalized instructions for diet and lifestyle modifications.

Perelman said, “I want people to know that there’s delicious food that’s incredibly healthy.”