I've read conflicting information about whether it's truly necessary to consume protein/carbs within 30 minutes of a workout, which I think is the basis of your question. Or whether as long as your overall diet is sufficient, it doesn't matter.

I've been fasting on Mon/Wed, and these are usually the days when I do recovery (i.e. slow) runs. I will run once or twice on these days, with my single meal in between. Typically I'll get up, have coffee (black), work an hour or two, then do a mid-morning run of 6-7 miles (about an hour). I'll have my meal around 1 PM. I then do a second run in the evening of 4-5 miles (about 40 mins).

My "meal" on fasting days is typically a nutribullet shake of spinach, frozen blueberries, banana or apple, cocoa powder (no sugar), unflavored whey protein powder, cashews or almonds, and two tsp of fish oil. My Fitness Pal says its ~ 600 calories, 27g fat, 60g carbs, 34g protein.

I'll have a second black coffee in the afternoon, and a green tea in the evenings.

How do you avoid losing weight given your exercise level and low calorie intake?

I am currently losing weight (slowly), about 5 lbs since I started. But to answer: I eat more calories on the days I'm not fasting. Let's do the math:

At my age and weight, I need ~ 1900 calories/day to maintain my weight assuming I'm sedentary. That's 13,300 calories/week.

I run 76 miles per week. That's about 7,600 calories.

So 20,900 calories a week. On two days I restrict myself to 600/day, so that's 19,700 across the other 5 days, or 3,940 calories on those days. But I've been losing about 0.5 lb/week, which is a deficit of about 1750 calories/week. So on those other 5 days I must be around 3600 calories.

3500-4000 calories a day is a lot, but not extreme, just ask any weight lifter. And I happen to really enjoy food. So it hasn't been a problem.

But, I may have to reduce my fasting to 1 day a week once I reach my goal weight.

Yes I was curious about the 30 min "rule". Thanks for the detailed info.