Federal wage and hour law does not mandate that employees be given either paid or unpaid rest or meal periods. Whether breaks are required is left up to the states. The only provision requiring meal or rest breaks in Iowa applies to employees under the age of 16.
U.S. Department of Labor Wage and Hour Division regulations do specify when work breaks including meal periods, rest periods, and sleeping time, if provided, must be counted as work time subject to federal minimum wage and overtime requirements (29 CFR 785.18 through 785.23). There are details on these requirements.