Your eyes are not deceiving you in the grocery store. Yes, your bag of Doritos just got bigger. No, the price didn’t change.

Last year, food packages shrank as food makers, dealing with record high ingredient costs, struggled to maintain their profits. But the weakened economy has caused a slump in demand for ingredients like corn and oil, pushing those prices back down. With lower ingredient costs — and higher consumer demand for more value — some brands like Frito-Lay are shifting back to bigger packages, without raising prices.

Think of your food packages like an economic barometer: Times are tough, so costs are low and packages are bigger. When times are good, costs are high and packages, to compensate, get smaller.

Tough times also mean consumers have less money to spend, so they want those bigger packages. Experts say this is a promotional tool that helps branded food companies steer shoppers back to their products and away from less expensive, store-brand alternatives.

Here are some questions and answers about the changing size of food packages.

Q: What’s getting bigger?

A: So far, the most evident size boosting is in the chip aisle, where Frito-Lay dominates. The company has boosted some package sizes for brands like Doritos, Cheetos, Tostitos and Fritos by 20 percent, reversing cuts made to bag sizes last year. Bags on shelves feature a thick white stripe announcing this.

Certain Doritos flavors have gone from 12 ounces back to 14.5 ounces, while Fritos bags are now 17.5 ounces, up from 14.5 ounces, and Cheetos are 10.25 ounces, up from 8.5 ounces. Tostitos are now 15.625 ounces, from 13 ounces. The pricing was unchanged, ranging from $2.89 to $3.99.

The company, a subsidiary of PepsiCo Inc., wants to return value to consumers, spokesman Chris Kuechenmeister said. He said Frito-Lay was unsure if these changes, originally taken about six months ago, would be permanent.

Elsewhere in the chip aisle, The Snack Factory increased the size of some of its pretzel crisps line by 25 percent, to 7.5 ounces from 6 ounces, earlier this summer.

Offering more for the same price is one way to boost sales since consumers are so focused on saving money right now, said Christopher Shanahan, a research analyst with Frost & Sullivan. Food companies can play up their value to consumers by offering larger-sized packages, which cost less on a per-ounce basis, he said.

Experts say offering larger sizes — along with other methods, like coupons or buy-one-get-one-free promotions — can convince shoppers who are trying to save money to stick with name brands.

Q: Why not just cut the prices? I’d rather save money than get more chips.

A: It’s not that simple, pricing experts say. Once prices are lowered, it becomes very difficult to raise them, since consumers may react negatively to that.

Instead, companies can give people more for the same amount of money, making for a per-ounce price cut, but leaving prices unchanged.