You'll probably find that this is a contentious topic, and there are a few other threads on the same topic that devolved quickly.
But here's me:
I lost my first 50 lbs by cutting down on packaged/processed food and eating take out and pizza 4 nights a week. And biking. And training for triathlons.
In 2013, the doc challenged me to lose 40 lbs or go on meds for life. He recommended South Beach, which focuses on less refined sugar, more whole grains, lean protein, and good fats. I hit his goals, bringing my net loss to -90 lbs and maintained under 200 lb for a little over 2 years. I'm up to 203 at the moment. I suspect some of that is muscle gain.
Overall I find that my performance is far more consistent (and not hindered) by making my carb selections more carefully. On event days and long rides, I do consume gels and G2/HEED and clif bars.