Bite an apple and, if you are healthy, here’s what happens: Specialized beta cells in the pancreas sense the glucose in your blood and squirt out insulin. The insulin attaches to receptors on your muscle cells, much like a key slipping into a lock, and opens the door, ushering in glucose for use as fuel

In Type 1 diabetes (a largely genetic autoimmune disorder in which immune cells attack the pancreatic beta cells) the body ceases to produce insulin. In essence, the key is lost. But in prediabetes (a condition diagnosed when blood sugar reaches levels high enough to damage delicate tissues in the eyes, nerves, and joints) and in Type 2 diabetes (which makes up more than 90 percent of diabetes cases and also is largely attributed to lifestyle choices) the problem tends to be on the receiving end. “Your beta cells are functioning and you have all this insulin in your system, but for some reason, the insulin cannot get that glucose into your cell,” explains Bonnie Jortberg, RD, a diabetes educator with the University of Colorado in Denver. The cells have become “insulin resistant.” As a result, excess sugar (a source of oxidative stress in the body) builds up in the bloodstream, wreaking havoc on internal tissues. Meanwhile, the muscle cells (where that sugar belongs) starve, prompting fatigue.

“The saturated fat that builds up in the cells is very much like chewing gum in a lock,” explains Barnard. “It interferes with insulin’s intracellular signaling process.” Studies have shown that high levels of fat circulating in the blood stream of even lean, young people can interfere with cell signaling and prompt insulin resistance within hours.

To make matters worse in the long term, excess stored fat, or adipose tissue, has a metabolic life of its own, emitting proteins that influence appetite and fat metabolism, cause inflammation, and interfere with insulin action, setting up a vicious cycle of weight gain and worsening blood sugar. “Fat used to be considered an inert storage organ, but we now understand this tissue is producing hormones and other substances that have a huge impact on our organs,” says Preeti Kishore, MD, an endocrinologist with Albert Einstein College of Medicine in New York. Too much dietary fructose, whether in the form of high fructose corn syrup or honey, also contributes significantly to stored fat, says Bob Rountree, MD< Delicious Living’s medical editor, so it’s wise to go easy on sweets as well.

This notion of stored fat as culprit has caught on so much in recent years that many diabetics have turned to gastric-bypass surgery. A 2009 review of 600 studies showed 78 percent of patients had a complete resolution of their diabetes after surgery. (Follow-up studies are underway to determine how long that remission lasts.) But Barnard and others insist there’s a better way.