Freezing temperatures makes you hungrier

At temperatures value of 0.15 and below, your saturation and hunger starts depleting even when idle. The depletion rate is fairly like that of mining or hitting a mob every second (20 ticks).. And to prevent this, simply either wear a full set of armor or only 1 piece of leather armor should do the trick.

Note: This is realistically because cold temperatures makes your body use more food to convert it to heat energy. On the other hand, hot temperatures makes your body use more water to cool down (except water bar doesn’t exist in minecraft yet).