Update only modified fields in Entity Framework

I'm working on a website on ASP.NET MVC4 and EF5. I want to ensure that only modified values are updated in the database. I'm using a unit of work pattern and repositories for data work. Here's the code for a generic repository. I've two questions, and need a code review for the following code.

1. Is the code to update only modified fields good? It works, but I don't know if this is the best way. I especially don't like that I have to do this loop through the properties myself (can't EF do this?). I also don't like the cast to object and the comparison.

2. How are my Add and Update methods? I'm planning the clients (MVC/API controllers) to use a service (passing in a unit of work) to get the work done. They will not directly use the repository. The repository will not have a Save() method, only the UnitOfWork will have one. I can ensure within the service that I will use the same context to update/add entities. Given this, are there any scenarios where my Add/Update code is going to fail?

public class EFRepository<T> : IRepository<T> where T : class
{
    protected DbContext DbContext { get; set; }
    protected DbSet<T> DbSet { get; set; }

    public EFRepository(DbContext dbContext)
    {
        if (dbContext == null)
            throw new ArgumentNullException("dbContext");
        DbContext = dbContext;
        DbSet = DbContext.Set<T>();
    }

    public virtual void Add(T entity)
    {
        DbContext.Entry(entity).State = EntityState.Added;
    }

    public virtual void Update(T entity)
    {
        //dbEntityEntry.State = EntityState.Modified; --- I cannot do this.

        //Ensure only modified fields are updated.
        var dbEntityEntry = DbContext.Entry(entity);
        foreach (var property in dbEntityEntry.OriginalValues.PropertyNames)
        {
            var original = dbEntityEntry.OriginalValues.GetValue<object>(property);
            var current = dbEntityEntry.CurrentValues.GetValue<object>(property);
            if (original != null && !original.Equals(current))
                dbEntityEntry.Property(property).IsModified = true;
        }
    }

    //... Other methods ...
}