Ensure is a highly processed food, and contains a lot of sugar (about the same amount as a soda.) In my opinion, it's little more than a chemical slurry. I think it would be far superior to employ a diet rich in whole foods where you can choose the amount of sugar, fats and additives. A dietician could help you come up with choices to help maintain muscle mass.

I've seen a lot of older folks who have depended on Ensure and other such drinks for their nutrition, and I can't say that any of them have thrived on it. Sure it's OK for a few days if you are recovering from an illness or surgery, but as a planned daily part of your diet, no, I wouldn't think it's a great idea.

Just my opinion.