LOOMIS SAYLES INVESTMENT GRADE BOND FUND

(the “Fund”)

Supplement dated December 30, 2020 to the Fund’s Summary Prospectus and Statutory Prospectus each dated May 1, 2020, as may be revised or supplemented from time to time.

Effective December 31, 2020, the Fund will add the Bloomberg Barclays U.S. Aggregate Bond Index as a secondary benchmark.

Accordingly, effective December 31, 2020, the first paragraph within the section “Risk/Return Bar Chart and Table” in the Fund’s Prospectus is amended to include the following sentences:

The Bloomberg Barclays U.S. Aggregate Bond Index is an unmanaged index that covers the U.S.-dollar-denominated, investment-grade, fixed-rate, taxable bond market of SEC-registered securities. The index includes bonds from the U.S. Treasury, government-related, corporate, mortgage-backed securities, asset-backed securities, and collateralized mortgage-backed securities sectors.

Effective December 31, 2020, the “Average Annual Total Returns” table within the section “Risk/Return Bar Chart and Table” in the Fund’s Prospectus is amended to include the following:

Average Annual Total Returns (for the periods ended December 31, 2019)	Past 1 Year			Past 5 Years			Past 10 Years			Life of Class N (2/1/13)
Bloomberg Barclays U.S. Aggregate Bond Index2		8.72	%		3.05	%		3.75	%		2.86	%

² Effective December 31, 2020, the Bloomberg Barclays U.S. Aggregate Bond Index became the Fund’s secondary benchmark.

Effective December 31, 2020, “Appendix C - Additional Index Information” to the Fund’s Prospectus is amended to include the following:

Bloomberg Barclays U.S. Aggregate Bond Index A broad-based index that covers the U.S. dollar-denominated, investment-grade, fixed-rate, taxable bond market of SEC-registered securities. The index includes bonds from the U.S. Treasury, government-related, corporate, mortgage-backed securities, asset-backed securities, and collateralized mortgage-backed securities sectors.