One word for "more you try, worse it gets"?

Is there a word for "more you try to improve, worst it gets"? Here is an example sentence - "Being on a diet may help reduce weight but it overall worsens your health".

The activity is self-defeating. Oxford English Dictionary:

Of an action or activity: preventing attainment of the end it is designed to bring about; futile or counterproductive.

So even though the diet is intended to bring about weight reduction, certain diets may cause weight gain or other health problems, thereby preventing attainment of the original goal of the activity.

Example:

While at first the diet helped me lose weight, the diet ended up being self-defeating; I gained back more than I lost.