ACCESS 2010 Update always updates the Update_Date

I'm running an Update query in Access 2010. EVen if there are no changes to data it will update the UPDATE_DATE with the current date and time. Is there some checksum I can use so this will only truly happen if data changes?

Code is

UPDATE tbl_Clients AS C INNER JOIN Audit_MasterClient AS A ON C.VisionClientID = A.[Vision Client Id]
SET
C.VisionClientID = A.[Vision Client Id], ClientName = A.[Client Name],
C.ParentCompany = IIf (A.[Parent Company] IS NULL,A.[Client Name],A.[Parent Company]),
C.BusinessSubLine = A.[Business Sub Line], C.SensitivityRating = A.[Sensitivity Rating], C.SensitivityratingReason = A.[Sensitivity Rating Reason],
C.RelationshipManager = A.[Relationship Manager], C.ClientAdvocate = A.[Client Advocate], C.ClientServicesDH = A.[Client Services DH],
C.CAM = A.CAM, C.RSDeptHead = A.[RS Dept Head], C.CRA = A.CRA, C.ERISAConsultant = A.[ERISA Consultant], C.TotalAssets = A.[Total Assets],
C.SiebelID = A.[Siebel ID], C.UserID = UCASE([txtUserID]), C.UpdateTS = NOW();