he doesn't need to take weight gaining shakes, just regular protein shake will do fine. Having low body fat % is not a bad thing, he can get cut easily.
I have a low body fat % and used to take weight gaining shakes
1. It didn't work
2. Gave me hard shits
3. I'm not sure chuging down 1000+ calorie shakes everyday is very good for you
i don't think he's looking to get cut, he's trying to put on mass. at 5% you have to be pretty f'ing cut even if you have almost no muscles. unless you're eating large meals every 3 hours, you need to take a weight gain shake. it's cheaper/more effective/less fat calories than the alternative.
1. if it didn't work out for you, you might not have been working out hard enough, or it might just not have worked with your bodytype.
2. drinking lots of fluids, and eating something like bread with the shakes helps with the shits... your body will also just adjust... give it time.
3. the only health concern with the weight gainer shakes is the large amounts of protein that can clog up the kidneys, but protein is key to gaining mass. so again drink lots of fluids to keep the kidneys flushed. otherwise the shakes are just healthy, clean, carb and protein calories.