For your body build and type, it makes sense to tinker with IF for the other documented benefits (insulin sensitivity, longevity, fasted workouts, and the host of other hormonal/endicrinological benefits).

But if you are looking to gain muscle mass, I'd just concentrate on really cleaning up the food quality, increase calries, and maybe dial down the crossft? 4-5 dys of crossfit is alot for tryin to ADD mass.

I'd agree with Danny and LiveForIt's answers - and just add that IF can release HGH, so IF'ing a couple of times a week, but maintaining calorie levels (probably by two big meals in a short time window of say 4 - 6 hours), may assist you in adding mass. I also agree that CF 4 or 5 times a week is too much, it doesn't sound like sufficient recovery. Fewer, more intense sessions, would probably assist you in adding mass.

IF for gaining lean mass is about collapsing your primary eating window into a 6-8 hour eating window following your workout. Martin's ideas at leangains.com have heavily influenced how I eat.

For example, today I worked out around 8pm, then over the next 5 hours or so ate:

1. 2/3 lb grassfed beef, 2 eggs, and ~300 gram yam cooked with 1/2 stick butter (~1100 kcal)
2. 500 grams fage yogurt, handfull flax + pumpkin seed granola and 1/2 pint of blueberries (~800 kcal)
3. 1/2 pint haagen-dazs five (~400 kcal)
4. 3 grams krill, zinc & magnesium

I was hungry this morning after playing a little basketball, so I also ate 2 eggs, 3 strips bacon and small sourdough roll with goat cheese (~700 kcal)

I am 6' and a lean 176 pounds, and this is a very satiating amount of food for me. I run or play basketball most days of the week and do a 20 minute chin/dip/squat & sandbag workout as well most days. I have not experienced any stress or cortisol issues that Robb Wolf may have mentioned in his podcasts.

I've found it pretty easy to gain lean mass on this sort of protocol if I

1. Take BCAA's pre-workout (about 0.2 grams per kg of bodyweight)
2. Eat a significant amount of carbohydrate in my first post-workout 'meal'
3. Add fat to everything (coconut milk/butter, grassfed butter, fish oil)

Regarding fat consumption, Volek and Kraemer have a good read Testosterone and cortisol in relationship to dietary nutrients and resistance exercise.

The sample size is small, but the 4 subjects with the highest testosterone (22-24 nmol/L) consume far more fat and less protein than the 7 subjects with moderate testosterone (12-17 nmol/L). See Table 3

I think it's fine, but when your activity levels are high, eat more

alot of people use IF for weight loss, where they don't replace the calories they skip

you can gain the hormonal advantage of IF without weightloss by replacing the calories

personally when I'm not trying to drop the vanity pound back off, I will train fasted, then eat big after, if I get soft, I don't eat heavy after...