If you drink milk, and yeah, a multivitamin, you're good to go. Pretty much covers all your body needs. I've been doing it for almost 2 years. No issues, and my bloods came out fine at my health checkup.

In the 18th and early 19th centuries, (before the Great Famine) lots rural Irish families lived for decades on a diet that was overwhelmingly potatoes + buttermilk/milk. They often ate 5–8+ pounds of potatoes per day. This diet was credited with keeping them relatively healthy and producing tall, strong men (many Irish were prized as soldiers/recruits partly because of it).