Food bar will not fill over 3 and a half

When i spawned in i had aprx half full food bar. when it got down to aprox 3 i ate a cooked chicken and it gave me 4 food icons but wold not allow me to eat until the bar was full. After this the bar would only allow me to eat when i had 3 food bar icons left and no matter what i ate it now wold only give me half a food bar to make 3 and a half.