In aged male mice, a 12-week diet supplemented with glycine and N-acetyl cysteine (GlyNAC) is associated with improved mitochondrial function, including increased expression of NDUFB8, elevated CPT1b and CrAT enzymatic activity, and reduced protein carbonylation, and these changes are associated with modest improvements in diastolic heart function; no such associations are observed in aged female mice.

In older male mice, GlyNAC gives the body more building blocks to make a key antioxidant called glutathione. This lowers harmful oxidative damage in heart cells, which lets mitochondria burn fat more efficiently and repair their energy-producing structures. At the same time, a protein that controls heart tissue stiffness increases, making the heart muscle more flexible during relaxation. These changes together improve how well the heart fills with blood between beats. In older females, glutathione levels are already high, so adding GlyNAC disrupts the natural balance, damages mitochondria, and weakens heart performance.