Diabetes is basically a fuel-distribution problem, says Duke endocrinologist Mark Feinglos, MD. “If you have a problem processing fuel, and you put too much fuel through the line, you flood the engine.”

Normally, the body breaks food down into glucose (sugar). The hormone insulin helps transport this glucose inside the muscles and other tissue cells, where it can be converted into energy to power everything from your morning walk to your chewing and swallowing at suppertime.

People with type 2 diabetes have too much glucose circulating in their blood, because some combination of two things is happening: The pancreas isn’t producing enough insulin to manage the glucose made from food, or the tissues (mainly muscle and fat cells) are becoming resistant to insulin so they can’t effectively use that glucose for energy.

These malfunctions are what’s behind the elevated blood sugar levels that physicians measure when diagnosing diabetes; over time, this excess glucose causes damage to organs such as the eyes, kidneys, and nerves.

Medications can improve both insulin secretion and insulin sensitivity. But if a person on these medications doesn’t lso change his or her diet and activity level, the enhanced glucose transport can actually make the problem worse, Feinglos says. “Your medications are going to facilitate transport of the caloric energy you need. If you don’t ontrol the number of calories you eat compared to how many you burn off, those extra calories are going to be efficiently stored, which means you’re going to gain weight.”

And because weight gain makes insulin resistance worse, it will eventually override the effects of the medication.

This means that, without lifestyle modification, there is simply no medication that will effectively treat type 2 diabetes. Though changing behavior is difficult, it’s essential to managing this disease.