I was having the same problem myself as you. After my fast ended (aro 5pm) I had a tendency to take the notion that "anything goes" and its time to tear up some food. Which I did. Although I stuck to paleo foods, I was easily exceeding my regular maintance cals in only 3 meals b/t 5pm and bedtime. Afterall, I fasted all day so my body needed the nutrients (that is what I was telling myself anyway). I quickly noticied a small drop in my performance and gradually started losing the visible top 2 ab muscles I had showing. So here's what I did (working very well so far).
On feed days, I follow strict zone eating (paleo foods only) at 3x's fat. As accurate as possible. So EOD I fast from 8-8:30 at night to 5pm the next day. After 5pm, instead of going buck-wild, I'll have a protein/high fat meal followed by another protein/high fat meal about 2 hours later. Cut out the carbs on the fast days (veggies only). This small change has made a huge difference. I guess without any sugar (fruits) or complex carbs my body wasn't craving more food and more carbs. Since your body is also more insulin resistant following a 20 hr fast, its critical not to eat too much and sending your blood sugar levels through the roof (which I did and set me up for more failure for the rest of the night).
So in short, maybe you can try dropping the carbs on fast days and concentrate on protein and fat meals only and see how that works.
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