I'm a 4 month convert to paleo after being off and on low carb for the better part of 6 years. i love what it's done for me as far as the body comp and the general way i feel. i can see myself eating this way for the rest of my life.
i am 6' and now weigh 255 with 210 lbs of lean body mass. my workouts are 3 days of powerlifting and 1-2 days of cardio a week. being that i like the amount of lean body mass that i have, i take in somewhere between .8-1.1/g of protein per lb of lean mass a day from free range eggs, grassfed beef, lamb and lots of fish. recently i've started messing around with IF. right now i do 18 hour fasts with 6 hour windows once or twice a week. when i do IF, i have a hard time squeezing in my normal amount of protein. If i started IFing more, am i in danger of losing some of my lean body mass?
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I think you'll be fine. Remember multiple animal studies have shown that muscle tissue is the last tissue to be used - as long as it is stimulated to growth sufficiently often.
Starved rats put through their paces lose fat but preserve muscle, but starved sedentary rats lose both.
Can't find the exact source at the moment, but I've read De Vany and others argue just the opposite to the premise of your question. That is, IF actually promotes lean muscle gain and that worrying about your muscles "cannibalizing" themselves is unfounded. Just make up the calories after you break your fast.
I can only agree with what everyone above has said and add my n=1. I have IFed 36-48 hour, eaten to hunger and found that to be ~1000 calories, tried high and low protein and always while quite high fat and have been consistently gaining muscle throughout it all. I lift heavy weights 4-5 days a week and have experimented with Escalating Density, Slow Burn, Max Contraction and often use a combination of all of them. I think protein needs are overestimated most of the time. Keep lifting and I don't think you will lose muscle.
I am 6'0" and I started eating paleo almost 3 months ago. When I started, I weighed 168 lbs.; I weighed in yesterday at 159 lbs. I do not IF, but I don't force myself to eat either. I usually eat about 5 times a day and still manage to lose body fat, but maintain my strength. I'm pretty skinny, but as my friend put it "deceptively strong". I started curling 50 lb. dumbells last week and I bench about 185 (5-8 reps at a time). I was worried about losing strength and muscle with this type of diet, but I just saw a plateau and a decrease in energy for about the first two weeks, then after that things went back to normal. I lift hard with little to no rest between super sets, 6 days a week. I do 4 different split training days, then a day of rest then repeat.
When my back is better, I will probably start doing yoga again also (so a 5 day rotation, then a rest day).
I do not IF and I am burning a noticeable amount of fat while maintaining steady strength gains. :P
I eat in 4 hour windows most days, I've been steady increasing strength while doing so...but I have no problem downing a lb of grassfed moocow in a sitting...
I only eat when I'm hungry tho.. Some days that means I eat alot some times I've gone 48hrs without food...
Heavy intensity increases food cravings. If your body is turning to gluconeogenesis, you'll know because you'll CRAVE like no other hunger.