When my husband and I hit our late 40's, we noticed that eating the same portions of foods we were normally accustomed to, were starting to pack on the pounds.  So we started eating smaller portions of meats and upped the vegetables.  With the smaller portions of meats, we now eat more expensive, not cheaper, meats.  For example, we used to eat two AA T-bone steaks at a meal.  Now we share one large AAA ribeye steak.  We also buy the more expensive extra lean ground beef (used to be lean ground beef).  Can't say this would be the case if our metabolisms had not changed.....but I'm thankful that it did (love eating grilled steaks so much more now).  I won't live without some real animal protein in my diet...no matter the price.