You can have any "bad" food in moderation and stay healthy/fit. I've been doing it for years. Actually, having bad foods worked into your diet is key to adherence, which is above all else the most important thing for your diet.
The best diet is the one you can stick to, not some gimmicky bullshit where you eat "magic" foods or eliminate entire food groups.
McDonald's is food, by the way. And it's not the worst thing you can eat.
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