Some people like a rare steak while others want theirs well done. The protein in that meat doesn’t really change, but a study published in The American Journal of Clinical Nutrition suggests that cooking can influence the bioavailability of amino acids for older adults.
On separate occasions, 10 volunteers between the ages of 70 and 82 consumed beef containing 30 grams of protein. For one meal, the meat was cooked at 135 degrees for 5 minutes which is considered rare. The next time, it was cooked at 194 degrees for 30 minutes.
After eating, there was a lower concentration of amino acids in blood with the rare cut compared to the well-done preparation. This was associated with decreased protein synthesis. This effect isn’t the same with younger individuals where the degree of cooking doesn’t really alter amino acid bioavailability.