Robbie ate 4 teaspoons straight from the jar and within minutes he turned into a whirling dervish, a cyclone of hyperactivity. He was banging his head against a pillow on my lap one minute and the next tearing down the hall to throw toys around his room. The parents seemed all too familiar with this behavior and began making excuses. He gets like this when we have company, when he's overtired, when he's excited.

As a doctor, I immediately knew what the problem was - sugar. Robbie's parents had already figured out that indulging his sweet tooth lead to hyperactive episodes. But they didn't make the connection between the peanut butter and the behavior. I took the jar and showed them the label, which listed two different sugars (high fructose corn syrup and sugar). The parents were stunned and said they would be more diligent about cutting out the hidden sugars in their son's diet. When my husband saw Robbie's father a week later, he said Robbie was much calmer, was sleeping better, and was like a different person both at home and at daycare.

Most people do realize that sugar can cause hyperactivity, but what they don't realize is that sugar lurks where you least expect to find it and affects the human body in myriad ways. The sugar industry vehemently denies that sugar is hazardous to human health. Are the parallel increases in sugar consumption, obesity, and diabetes just a coincidence? Here are the straight answers.

I know sugar can lead to weight gain, but is it really all that bad for me?
Yes, it really is. Sugar is a simple carbohydrate found naturally in many foods, including fruits and grains. If the only sugar we consumed were in natural, whole foods, we'd all be just fine. But the average American diet is full of refined, nutrient-depleted foods and contains an average of 20 teaspoons of added, refined sugar every day. That's twice the amount recommended by the USDA (10 teaspoons and four times the maximum I personally recommend.)

So what's wrong with refined sugar? Many things. First, sugar compromises immune function. Two cans of soda (which contain 24 teaspoons of sugar) reduce the efficiency of white blood cells by 92 percent - an effect that lasts up to five hours, according to Kenneth Bock, M.D., an expert in nutritional and environmental health. Since white blood cells are an integral part of your immune system, if you happen to meet a nasty virus or bacteria within five hours of drinking a few colas, your immune system may be unable to fight off the invader.

Refined sugar also overworks the pancreas and adrenal glands as they struggle to keep the blood sugar levels in balance. When you eat sugar, it is quickly absorbed into your blood stream in the form of glucose. This puts your pancreas into overdrive, making insulin (which carries glucose to your cells to be used for energy) to normalize blood sugar levels. But this rapid release of insulin causes a sudden drop in blood sugar. In reaction to the falling blood sugar, excess adrenal cortisone is stimulated to raise blood sugar back to normal. A constantly high intake of simple dietary sugar keeps this roller coaster going and eventually overworks or "burns out" normal pancreas and adrenal function leading to early menopause, adult-onset diabetes, hypoglycemia, and chronic fatigue.