Based on the information available, there are several herbs that have been suggested to potentially improve protein metabolism and utilization in the body. However, it's important to note that more research is needed to fully understand the extent of these herbs' effects on protein metabolism.

1. **Spirulina**: This blue-green algae is a complete protein, meaning it contains all nine essential amino acids [1]. It has been suggested to improve protein synthesis and reduce protein breakdown [2].
2. **Maca**: This Peruvian herb is rich in amino acids, the building blocks of proteins. Some studies suggest that maca may help increase muscle mass and improve exercise performance, potentially due to its protein content [3].
3. **Ashwagandha**: This adaptogenic herb has been shown to increase muscle mass and strength in several studies, which may be due in part to its effects on protein metabolism [4].
4. **Turmeric**: The active compound in turmeric, curcumin, has been suggested to improve protein utilization and reduce muscle damage after exercise [5].
5. **Ginseng**: This herb has been shown to increase protein synthesis and reduce protein degradation in muscle cells, potentially improving muscle growth and recovery [6].

It's important to note that while these herbs may have protein-improving properties, they should not be used as a substitute for a balanced diet that includes adequate protein intake. As with any supplement, it's important to speak with a healthcare provider before adding these herbs to your routine.

Sources:

1. <https://www.drugpatentwatch.com/insights/spirulina-the-blue-green-algae-with-numerous-health-benefits>
2. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6892180/>
3. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6265971/>
4. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6771108/>
5. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5823032/>
6. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5852752/>