In Super Size Me, filmmaker Morgan Spurlock documented what happened to his body when he started eating at McDonald's three times a day
A physical exam prior to the experiment showed that Spurlock, who had been on a mostly vegetarian diet, was the picture of health. His cholesterol was 168 (most Americans struggle to keep their cholesterol below 200), and his weight was 185, with only 11 percent body fat instead of the 18 to 25 percent carried by a typical American male.
Within 30 days on a McDonald's diet his cholesterol shot up to 225, he gained 25 pounds, and his body fat increased nearly 65 percent.
Most alarming, however, was the change in Spurlock's liver, which had become fatty and inflamed — a condition his doctor termed "obscene."
Now Swedish researchers have revealed another problem brought on by the high-calorie, high-fat Super Size Me diet: insulin resistance, a precursor to Type 2 diabetes.
The researchers put 18 young, lean volunteers with no sign of insulin resistance on the Super Size Me diet for 30 days. The volunteers gained an average of 10 percent of their original body weight — about 12 to 15 pounds — half of it fat. And fat samples revealed that they had insulin resistance equal to people twice their age.
People naturally develop some insulin resistance as they age because their cells become less efficient at using sugar for fuel, but this research shows that weight gain combined with a fatty liver rapidly accelerates the process.
What's the connection?
One clue comes from people who undergo bariatric surgery for weight loss, says Dr. Anthony Morrison, an endocrinologist at the University of South Florida who treats people with diabetes. Immediately after surgery they start to experience a remarkable improvement in their insulin resistance.
"Their insulin requirements, even if they have diabetes, fall within seven to 10 days, long before any significant weight loss," says Dr. Morrison. "Why? I think the significant decrease in caloric intake allows the so-called fatty liver to use up the fat that has been stored in it."
With less fat in it, according to Morrison, the liver becomes more efficient at absorbing sugar from the bloodstream, and the pancreas adjacent to the liver becomes more efficient at producing insulin.
"When the liver is full of fat, it cannot absorb as efficiently carbohydrates and sugars circulating in the blood," he says. "This leads to elevated blood sugar."
Fasting produces the same effect, which may be why people who restrict their calories through intermittent fasting (eating normally one day and fasting the next) display improvements in blood pressure, cholesterol and other measures of health.
Exercise also promotes better control of sugar in the blood. A recent study of 14 sets of twins in which one twin was obese while the other was not found that the metabolic differences between them were most strongly linked to less physical activity by the obese twin.
The moral of this story is that people can minimize insulin resistance as they age by reducing the fat in their diet, eating less and getting more exercise. A relatively low-fat diet combined with smaller portions and a little exercise will help avoid a fatty liver, and a liver not already full of fat will absorb excess sugar from the blood more efficiently.
"I would speculate that the opposite would occur if I stuffed myself with Big Macs and fries," Morrison says. "By consuming an excess amount of fat, I'll start to have a fatty liver."
Tom Valeo is a freelance writer living in St. Petersburg. You can reach him in care of LifeTimes, St. Petersburg Times, P.O. Box 1121, St. Petersburg, FL 33731.