It's too early to recommend fasting for medical purposes, but the findings are provocative and warrant further study to understand the health benefits of this centuries-old spiritual practice, said the study's lead author, Benjamin Horne, director of cardiovascular and genetic epidemiology at Intermountain Medical Center in Murray.
"There are a lot of books out there recommending that people fast for two or three days a week," he said, "but there are risks with fasting and little evidence that these diets are safe."
Horne presented his findings Saturday at the American Diabetes Association Scientific Sessions in San Francisco.
Diabetes has become a major health threat. The number of Americans diagnosed surged to 29 million in 2012 from 26 million in 2010, according to the Centers for Disease Control and Prevention. Another 86 million adults, or one-third of the population, have blood sugar levels high enough to be considered pre-diabetic.
Utah's diabetes rate is rising, too, but the Beehive State ties with Montana for the second lowest rate in the country.
Utah also has a low rate of heart attack deaths, which has long been attributed to the fact that so few of its teetotaling Mormon residents smoke.
But states with comparable smoking rates don't necessarily rank as high as Utah on national health scorecards, so Horne and his colleagues set out to understand if other lifestyle factors were at play in the low diabetes rate.
Fasting stood out because The Church of Jesus Christ of Latter-day Saints encourages members to go without food and water for 24 hours once a month on Fast Sunday. Many religious groups embrace fasting as a demonstration of faith.
Since 2008, Horne's team has documented the health benefits of fasting in those who routinely fast and in those who had no prior experience with fasting.
For their latest study, they sought to better understand what happens in the body during fasting, specifically looking at metabolic changes.
They recruited 12 pre-diabetic Utahns and put them on a water-only fast one day a week for six weeks.
The participants were a mix of men and women between the ages of 30 and 69 with at least three metabolic risk factors: a large waistline, a high triglyceride (blood fat) level, high blood pressure and a high fasting blood sugar level.
Fasting had no effect on their blood sugar levels. But participants each lost an average of three pounds and researchers detected elevated levels of cholesterol in their blood, which likely came from fat cells. Excess fat is a major contributor to insulin resistance, which can lead to diabetes.
How, then, is a cholesterol spike a good sign? Because the spike was temporary, Horne explains.
"When you fast it switches your body from using blood sugar to using fats for energy. The body starts scavenging fat from wherever it can find it, temporarily increasing the amount of fats and cholesterol in the blood stream," he said.
After the full six-week period, participants' baseline cholesterol levels dropped by about 12 percent, the study showed.
"Burning fat cells means less of them are available to contribute to the development of insulin resistance," Horne said.
Horne plans to do a follow-up study to see if a longer or more intense fasting regimen would be more beneficial but equally safe.
His initial findings, however, suggest the latest weight-loss craze, intermittent fasting, or the 5/2 diet, may not help fight diabetes.
Intermittent fasting is the binge eater's dream, because it allows you to eat whatever you want on your non-fast days and calls for restricted not zero calories on fast days.
But Horne's study showed the metabolic benefits don't start kicking in until 12 hours into the fast, and they peak at 24 hours.
"So the last 12 hours is where you see the most metabolic benefit, and eating negates that benefit," he said.