Hello Elke,
Thanks for your question. According to the following study: Kelley, DS, and PA Daudu. “Fat intake and immune response.” Progress in food & nutrition science 17.1 (1993), a high fat diet would reduce the effectiveness of your immune response. The 30% of calories from lipids comes from the official Health Canada recommandations https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/fn-an/alt_formats/hpfb-dgpsa/pdf/nutrition/dri_tables-eng.pdf