JUST ONE JUNK FOOD MEAL CAN MEAN THE END

If you overdo it on pizza, macaroni and cheese, chips, and ice cream, you might worry about what it's going to do to your thighs or mid-section. But binging on junk food isn't only a matter of weight gain. It might have far more serious repercussions than that.

People who ate a diet focused on macaroni and cheese, processed lunchmeat, sausage biscuits, mayonnaise, and microwavable meals with unhealthy fats, for example, showed serious negative changes to their metabolism after just five days.

After eating the junk-food diet, the study participants (12 healthy college-aged men) muscles' lost the ability to oxidize glucose after a meal, which could lead to insulin resistance down the road

What Happens to Your Metabolism After Five Days of Junk Food

Even though their caloric intake remained unchanged, when men ate a junk-food diet their muscles' ability to oxidize glucose was disrupted in just five days' time. This is a significant change, because muscle plays an important role in clearing glucose from your body after a meal.

Under normal circumstances, your muscles will either break down the glucose or store it for later use. Your muscles make up about 30 percent of your body weight, so if you lose this key player in glucose metabolism it could pave the way for diabetes and other health problems. As reported by TIME:

"'The normal response to a meal was essentially either blunted or just not there after five days of high-fat feeding,' [Matthew] Hulver, [PhD, department head of Human Nutrition, Food, and Exercise at Virginia Tech Hulver] says.

Before going on a work-week's worth of a fatty diet, when the men ate a normal meal they saw big increases in oxidative targets four hours after eating.

That response was obliterated after the five-day fat infusion. And under normal eating conditions, the biopsied muscle used glucose as an energy source by oxidizing glucose. 'That was essentially wiped out after,' he says. 'We were surprised how robust the effects were just with five days.'"

Just One Bad Meal Can Mess with Your Health

Morgan Spurlock's documentary Super Size Me was one of the first to vividly demonstrate the consequences of trying to sustain yourself on a diet of fast food. After just four weeks, Spurlock's health had deteriorated to the point that his physician warned him he was putting his life in serious jeopardy if he continued the experiment.

But as the featured study showed, it doesn't take a virtual month to experience the health effects of a poor diet. In fact, the changes happen after just one meal, according to research published in the Journal of the American College of Cardiology.

When you eat a meal high in unhealthy fats and sugar, the sugar causes a large spike in your blood-sugar levels called "post-prandial hyperglycemia." In the long term this can lead to an increased risk of heart attack, but there are short-term effects as well, such as:

• Your tissue becomes inflamed (as occurs when it is infected)
• Your blood vessels constrict
• Damaging free radicals are generated
• Your blood pressure may rise higher than normal
• A surge and drop in insulin may leave you feeling hungry soon after your meal

The good news is that eating a healthy meal helps your body return to its normal, optimal state, even after just one. Study author James O'Keefe of the Mid America Heart Institute in Kansas City, Missouri told TIME:

"Your health and vigor, at a very basic level, are as good as your last meal."