Microbial biomass has emerged as a promising sustainable protein alternative. The cultivation conditions affect the composition of microbial cells, and hence their quality and nutritional value. Here, we investigated the relationship between growth rate, substrate availability and cell composition and size of Cupriavidus necator and Komagataella phaffii. Biomass with decreased nucleic acid and increased protein content was produced at low growth rates. Conversely, high rates resulted in larger cells, which could enable more efficient biomass harvesting. The proteome allocation varied across the different growth rates, with more ribosomal proteins at higher rates. Considering the distinct amino acid profiles established for the different cellular components, variations in their abundance impacts the product quality leading to higher cysteine and phenylalanine content at low growth rates. In summary, we demonstrate tradeoffs between nutritional quality and production rate, and we discuss that techno-functional food properties should be considered when designing microbial biomass production processes.