The following is an excerpt from the Zeroing In On Health blog:

We get these diseases because our immune systems aren’t up to the job. One way in which our immune systems are compromised is found in the so-called healthy carbohydrates we eat which lessen our white blood cells’ ability to mop up invading microbes. It is clear from these studies that, if you eat ‘five portions of fruit and veggies’ and base your meals on starchy foods, as we are all advised to do, you could lose a major part of your immunity to infection for the whole of the day.

Of all of the sugars, fructose (found in fruit and high-fructose corn syrup) was found to impair the immune system the most.  Steak and eggs just scored another point.