In August of 2012, my family and I took the Whole30 Challenge. For 30 days, we ate real food - no sugar, no alcohol, no grains, no legumes, no dairy, no white potatoes - just healthy meats, fruits, vegetables, nuts, and oils. (Here's what we ate.)
In 30 days, I lost ten pounds. Over the course of the next two months, as I learned how to incorporate some of those prohibitions back into my diet (and discovered ibuprofen makes me sick, sick, sick to my stomach) I lost another 10 pounds.
I have maintained that weight loss for over a year.