Betaine, also known as trimethylglycine (TMG) is an amino acid derivative commonly found in beets and spinach
It is shown to reduce high levels of homocysteine. High levels of homocysteine have been associated with atherosclerosis and heart disease
TMG has also been shown to increase strength and power output, in part because it acts as an osmolytic, maintaining cellular osmosis similarly to creatine. This is particularly beneficial to those on low carb diets.
Fun fact: farms supplement cattle fodder with TMG and lysine to increase the muscle mass of livestock