I'm no nutritionist, but intuition would suggest that it's actually quite healthy to eat the same animals that humans have been chomping on since the dawn of time. Maybe the problem isn't that we eat cows, it's that we eat mutant freak factory-farmed cows that have been pumped full of hormones, raised on diets of toxic garbage and tortured for most of their short lives? I'm only guessing.
With that being said, the thing that concerns me most about lab-grown meat isn't whether it's healthy, it's that if it ever gets popular then it's going to be controlled by a tiny handful of multinational megacorps who'll use it to crush independent food producers worldwide and enforce a brutal centralized control of something as basic to human survival our everyday protein consumption. They're the last people on earth we should trust to keep us healthy and satiated, and their claims that they're doing it for our or the environment's benefit (and not just their own greedy empowerment and profiteering) should be treated with extreme scepticism.