i have a altis 06 auto, with 55k on clock less drive, never faced this issue and there are also other members with high milage altis and not facing issue as well, only similarity between us we are using Mobil 1 5W-50 fully synthetic oil, so even with fully synthetic oil on long route no oil consumptions whatsoever. you should reconsider your oil viscosity as well as as brand or make sure you are not getting counterfeit product or locally packed product, what price did you pay for oil? 4 litre pack of 5W-50 costs around 5000rs, plus 1600rs for 1 litre pack extra as altis takes just a but more than 4 litres, i thin you got the wrong or cheap oil, also simply check your PCV valve it can also cause oil to reduce without any outward signs. i think correct oil will cure the issue, and 1zz-fe engines are know to slurp up some oil its mentioned in the cars owner manual as well so its normal and you don't have to worry, it might not have happened in the first place if you have been using correct oil since day one.