Americans are making costly grocery mistake even before entering the store, expert warns

A grocery shopping mistake that could be costing Americans money starts even before they get to the store, according to cookbook author Jenn Lueke.

"The No.

1 biggest mistake is just not taking the time to plan ahead," Lueke, Boston-based author of "Don't Think About Dinner," told Fox News Digital.

Making a grocery list and deciding what to cook for the week ahead can help shoppers save money and stress less about meals, she said.

SCIENTISTS SAY YOU'VE BEEN THROWING AWAY PERFECTLY GOOD MEAT BECAUSE OF ONE COMMON MISTAKE Another source of overspending may be the pressure to make a different, impressive dinner every night of the week.

Social media can offer inspiration but Lueke, known online as Jenn Eats Goood, said home cooks can lean on familiar meals and switch them up with ingredients already in their pantries.

CELEBRITY CHEF SAYS IF YOU CAN DRIVE TO MCDONALD'S, YOU CAN COOK HEALTHY MEALS AT HOME "You really can repeat meals," she said, adding that a "base recipe" can also be tweaked seasonally or depending on what is in your freezer at the moment.

One example from her cookbook is a one-pot chicken thighs and rice dish.

Lueke said cooks can swap in different proteins or add seasonal ingredients such as squash in the fall or asparagus and peas in the spring.

NEW PROTEIN RANKING NAMES UNEXPECTED WINNER OVER BEEF, SALMON AND EGGS A bowl-style meal or vegetable frittata can also serve as a flexible starting point for using up any food that is about to go bad, she said.

Keeping pantry and freezer staples on hand can give shoppers more options during the week, Lueke also said.

CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTER She recommends ingredients such as canned beans , rice, pasta and quinoa, which can be bought in bulk or picked up on sale.

Frozen proteins can also help cut down on weekly shopping trips.

TEST YOURSELF WITH OUR LATEST LIFESTYLE QUIZ For shoppers trying to stretch a $50 to $75 grocery trip, Lueke suggests bulking meals up with hearty, lower-cost produce such as carrots, onions, potatoes and sweet potatoes, along with proteins like chicken thighs, tofu and chickpeas .