How to introduce certain foods back into your diet?!

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Hi there. I'm currently doing a challenge at my gym where each week you cut out a certain type of food and don't eat it for the whole month. For example, I've gone a week without bread, pasta and rice and have three weeks left. I have no problem cutting these foods out for a month, but I know I'm going to want to bring them back into my normal diet (only wholegrain/wholewheat) after this month is over. I've heard so many stories of people cutting out things and then as soon as they start eating that food again, the weight goes back on. I really don't want this to happen to me as I have quite a bit to lose and I can't afford to gain it back. How can I introduce these foods back into my diet when this month is over without gaining back everything I worked so hard to lose? Any advice would be greatly appreciated :)