Does sugar weaken your immune system?
One study performed in 1973 showed that white blood cells from
individuals who had consumed 100 grams of sugar (about 20
teaspoons) were less active. This study has been cited for many
years as evidence that sugar suppresses the immune system, by no
less than the famous pediatrician Dr. Sears.
However, no studies have since proven that individuals who consume more sugar actually get more colds or flu. The way the body fights disease is extremely complex and the effects of sugar consumption on the immune system have not been definitively identified. The scientific consensus seems to be that eating a healthy, balanced diet and maintaining normal weight is the best way to sustain overall well-being, including reducing susceptibility to illness. There is little to no evidence that eating a candy bar or drinking a Coke will cause you to be acutely susceptible to disease.