According to the IRS definition, "per diem is a daily allowance for travel expenses and includes lodging, meals and other other incidentals. The IRS says that to qualify for per diem rates, the travel must be at least 50 miles from home and require an overnight stay."
Thus, if you meet the above definition, you would be able to deduct the amount spent on meals as part of your per diem. However, please be aware that this deduction would be reportable on Schedule 2106 and these amount are then included as part of the unreimbursed employee business expenses subject to the 2% AGI limitation as part of the Itemized deductions (Schedule A).
It would then be true to say that taxpayers who cannot itemize would not benefit from the Per Diem deductions.