The Secretary shall take such precautions as the Secretary deems necessary to assure that any eligible recipient agency receiving commodities under this chapter will provide such commodities to persons served by the eligible recipient agency and will not diminish its normal expenditures for food by reason of the receipt of such commodities. The Secretary shall also take such precautions as the Secretary deems necessary to assure that commodities made available under this chapter will not displace commercial sales of such commodities or the products thereof. The Secretary shall not make commodities available for donation in any quantity or manner that the Secretary, in the Secretary’s discretion, determines may, substitute for the same or any other agricultural produce that would otherwise be purchased in the market.