Sarah Frazelle, of Lawrence, stocks up at Aldi recently.

When it comes to shopping, Sarah Frazelle pays attention. The Lawrence resident peruses ads and checks pre-unit prices, suspicious of markdowns and sales.

“Sale prices can be deceptive, but most places are good about including the per-unit price to make comparisons easy,” she says. “I also tend to keep a mental list of prices for the items we frequently use and compare them in every store I’m in.”

Frazelle fights the urge to plunk down copious amounts on groceries, but habits like hers can be hard to come by.

The World Bank estimates that nearly a billion people live off a dollar a day, sometimes less, while the average American slaps down at least $7 for a day’s worth of food — more than $200 a month.

And then there are those who don’t have enough to spend. Many American families fetch below-average incomes, making it hard to stock the fridge, says Adam Drewnowski, director of the University of Washington Center for Obesity. Poverty-pinched families often end up buying foods rich in calories but low in nutrients: Ramen noodles, frozen French fries, hotdogs.

To get the best results from grocery shopping, people need to take the time to both plan and cook meals, Drewnowski says.

“They will need to have some cooking skills and some spare time,” he says. “I am saying that it’s probably worth it, but I can also see how this can be hard for many people.”

There are ways to trim the grocery bill and still achieve a healthy diet. Just ask Erin Chase, author of “The $5 Dinner Mom,” a cookbook crammed with recipes that can feed a family of four for under $5. Chase has developed a shopping system that’s allowed her to lop off hundreds of dollars from her yearly food budget.

Being prepared

Chase’s No. 1 strategy is awareness.

“My first basic rule is to not fall into the store’s marketing tactics,” Chase says.

Be suspicious of end caps, the tables at the end of aisles stocked with supposed deals. According to Consumer Reports, end caps are often used to get rid of foods that are an inch from expiring. So check the expiration date, or even better, trudge to the aisle where the product is usually located and see if the same deal applies for a fresher version.

Thinking ahead

“Meal planning is absolutely crucial for shopping well,” Chase says. “I shop based on what’s on sale.”

At the end of every week, Chase makes a list and a meal plan. Monday: Egg salad sandwiches; Tuesday: Sesame stir fry.

Chase is also big coupon clipper, but she doesn’t resign herself to what’s inside the newspaper. She also hops online to find promotional discounts. Most stores now supply some sort of digital coupon.

Stocking up

Buy freezer and pantry items whenever they’re on sale. But when you stockpile, it’s important to dip back into the freezer and actually use what’s in there: You don’t want to chuck out a pot roast a year from now because it’s laden with freezer burn.

Store hopping

Some stores have better deals on certain items, so keep an eye on store ads and compare prices. Amanda Pratt, 23, is an Aldi shopper. On grocery day, she tramps to the store and stalks through the aisles, her purse stuffed with mesh bags for the ride home.

Aldi is way cheaper, Pratt says. It lets her save by buying lesser-known brands. Plus, the do-it-yourself bagging eliminates the need for a plastic grocery sack that she would probably just throw away.