I can't comment on the fat-prostate issue, as I am not qualified to give medical advice. But I understand your caution. MFGM content of full-fat greek youghurt will be higher than in the low-fat version. But MFGM content in youghurt is anyway very low compared to milk. Greek youghurt has a higher concentration of proteins than the regular yoghurt, as itiis strained twice. So, it is an excellent choice for protein supply. I wouldn't be too much worried about the fat. Of course, it tastes better, because fat is generally the carrier of flavors.