on a diet

on a diet

Participating in a specific nutritional plan typically consisting of eating smaller amounts of food, eating (or avoiding) particular foods, or both in an attempt to lose weight or achieve some other health benefit. A: "Would you like some of my lemon meringue pie?" B: "No, thank you. I'm not a diet." My doctor put me on a diet of nothing but fruits, vegetables, and nuts.
See also: diet, on

*on a diet

trying to lose weight by eating less food or specific foods. (*Typically: be ~; go ~; put someone ~; stay ~.) I didn't eat any cake because I'm on a diet. I'm getting too heavy. I'll have to go on a diet. I have a lot of trouble staying on a diet.
See also: diet, on