Weight

Weight is a stat that was added in update v0.29 along with strength, athleticism, and sanity. In update v1.0, weight, along with calories was made exclusive to hard survival mode. It is not in normal mode or hard mode.

Gameplay
Currently the starting weight is 205 pounds, max weight is 305, lowest weight is 155 and you are overweight when your weight is 210 or more. Weight is updated once per day, that time is dependent on when your character started the game. In single player, this is every morning at sunrise. In multiplayer, this will differ for when you originally joined the game. For example, if you joined at night time, your weight will update at that time, every night for the rest of the game.

Weight seems to have no beneficial effects to your character, but it does have negating and limiting effects on other stats. For example, being overweight will impede and in some cases completely halt the progression of other stats like strength, and will greatly affect athleticism. Unlike with strength and athleticism, weight has no obvious influences over the physical playing of the game. Excessive weight can lower the strength stat, with excessively higher weights greatly reducing the rate of athleticism gain. Become too heavy, and it will stop rising.

This can be a very difficult stat to manage, as it fluctuates very gradually, and thus is hard to keep a large amount of control over. With the introduction of calories, it is now more difficult to maintain. Weight will rise if your calorie amount is in the positives, the amount it will raise is dependent on how much extra calories you have. If you are under, then you weight will lower, dependent on how much exercise you've done.

To lose weight you have to spend all extra calories until the weight update time (mentioned above) and make sure that the symbol next to your weight amount shows points decreasing. If your caloric intake is less than your spent calories until the next day, you will lose weight. If your caloric intake is more than the calories you spend, you'll gain weight.

When losing weight, you should not continue to burn calories once all consumed calories are spent because this interrupts strength gain and can also cause strength loss. Swinging your weapon or tool is one of the best ways to burn calories. Keep in mind, if you have burned all consumed calories, this will lower your strength.

Mechanics
Information on how calories influence weight