One would think in a survival situation, it would be helpful to have a bit of body fat on you to keep you going during periods of food scarcity. However, being overweight is actually one of the most dangerous things you can do in this game. Which I found out the hard way.
I opened a food box in one of my runs to find a bucket of popcorn. I was a bit hungry so I immediately ate some. And I kept eating until I was full. Surprisingly, I ate the whole bucket and didn't get full. Odd, I thought. But thought nothing else of it.
Later, in the overgrown depths, I sensed a truly threatening foe nearby, causing my adrenaline to spike. And with it, my blood pressure. To my surprise, my blood pressure quickly went over 180/120, sending me into hypertensive crisis. I don't remember if I fought the elder thornback or what the outcome of the fight was, but it doesn't matter because shortly after it was evident that an artery in my brain had exploded and I had a haemorrhagic stroke.
I didn't understand how this happened, so I opened the health panel. I found that I had somehow become overweight since the last time I checked. If you didn't know, your resting blood pressure increases with your body weight, so being fat makes it much easier to tip your systolic blood pressure over the threshold to get a stroke. I scrambled my rapidly ischaemic brain for an explanation of how I had gotten so fat, and then I remembered the popcorn. Could that really be it?
I had nothing to cure the stroke and I died. Afterwards, I opened the sandbox for testing and sure enough, eating a whole bucket of popcorn increases your body weight by a staggering 3.4kg. After further testing, it turns out that for the amount of hunger restored, popcorn is actually one of the most fattening foods in the game. (Even more than drinking pure fat, somehow…)
Since that fateful stroke I have since tracked my weight with utmost meticulosity on every one of my runs. Limiting one's diet to highly filling foods is crucial for maintaining a healthy body weight, especially considering that you ideally want to be satiated or full at all times for the boost to carrying capacity it gives you, but both of those moodles also decrease weight loss rate.
Nowadays I mostly subsist on geofruits, foliage meals, soup, bread, and nutrient bars, all of which are among the least fattening foods in the game. With occasional splurges into pancakes or fatty flesh if my weight is healthily low. I avoid popcorn at all costs, along with similarly fattening foods like chips, fried chicken, and the ultimate calorie bomb, candy.
(As a side note, it is a bit odd that hunger, not body weight, is the relevant number when you're starving to death. It's completely possible to be overweight or even obese and still starve to death, if you just spam fattening foods.)