There are nine essential amino acids that humans must obtain from their diet because the body cannot synthesize them in sufficient amounts. These nine essential amino acids are:

• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

These amino acids are crucial for various bodily functions, including protein synthesis, muscle repair, immune function, and neurotransmitter production

. In summary, the number of essential amino acids for humans is nine.