The former Destiny`s Child singer works out as often as possible but insists she doesn`t do so in order to be as thin as possible.
She said: "It`s not all about dress size but also about being healthy as well. I`ll never be a size zero. I`m happy being a size 10, but I want to be healthy.
"I work out every other day at least. If you don`t then I don`t think you see the rewards. Even if you can get 30 minutes of cardio in every other day you`ll see a big change in yourself.
"While it`s great to have a routine, it`s important not to limit yourself to certain times of day. It`s easy to get home from work and say, `Oh, I`ve missed the gym.` Do 30 minutes on the bike or some sit-ups.
"I am a big believer in keeping the body toned. Twenty minutes each on the bike and the cross trainer are great for that. Also sit-ups are the only way to a flat stomach."
Kelly follows a healthy eating plan, but doesn`t believe in depriving herself of her favourite foods.
The `X Factor` judge insists it`s important to treat yourself on occasions because complete deprivation doesn`t work.
She explained to new! magazine: "There`s a great diet called the 80/20 diet, which means you make sure 80 per cent of the stuff you eat is good and the other 20 per cent is your choice. It`s great because it means you`re not depriving yourself of anything.
"Breakfast is very important, and I`ll start with porridge. Lunch will probably be my most calorific meal of the day to give me energy at work, like tuna pasta, and then at dinner it will be a very light grilled chicken or fish with vegetables."