Weakening the Health Argument

In a recent blog post, a healthy eating advocate wrote, “Eating more fruits and vegetables is the best way to improve your overall health. Studies show that people who eat a diet rich in these foods have fewer health problems than those who do not. Therefore, if you want to be healthy, you should eat more fruits and vegetables.”

The argument concludes that increasing fruit and vegetable consumption will lead to better health. Which of the following, if true, would most seriously weaken the argument?