They are not being starved, but hungry is a real and fair description of how most inmates feel, and there is a specific reason for that.
Jail and prison meals are required to meet a minimum nutritional standard of roughly 2,000 calories per day. That requirement is taken seriously because facilities face legal exposure if they fall below it. The food is not good; it is not meant to be, but it checks the nutritional box on paper.
The problem is that 2,000 calories sounds like enough until you realize what most people are eating on the outside before they come in. Three full meals, snacks, fast food, drinks with calories, and portions that are significantly larger than what gets served on a tray in a county jail. The body does not adjust overnight. For the first weeks and sometimes months, inmates feel genuinely hungry even though they are technically getting fed.
A typical day looks something like this. Breakfast is a rotation of oatmeal, grits, cornbread, bread with jelly, and a piece of fruit. Lunch is usually a sandwich with bologna or a similar processed meat, maybe hot dogs, a chicken patty, tuna, or sardines, sometimes with a small bag of chips. Dinner is the most substantial meal, often something like a piece of chicken, spaghetti, chow mein, meatloaf, or potatoes with bread on the side.
It keeps people alive and functioning. It does not keep anyone satisfied.
The most practical thing you can do is put money on his commissary account so he can supplement the trays with snacks, ramen, tuna packets, peanut butter, or whatever his facility stocks. That is exactly what gets most inmates through. Even a small amount makes a meaningful difference in how the day feels.