"Things are not always what they seem."
It's a famous adage used by countless authors of thrillers to create instant intrigue and mystery.
But what if it applied to the labels on common food products? And rather than intrigue, it raised outrage from consumers and health concerns by the Food and Drug Administration?
That's been the result as some food producers have been watering down their products or substituting cheaper ingredients to save some cash, the FDA says.
Olive oil, honey, maple syrup and fish are among some of the most common culprits.
Olive oil is one of those rare foods that tastes heavenly but is also healthy -- if it has not been altered with other ingredients that are.
"If that product is diluted with other fats, people are simply getting ripped off and not getting the health benefits that they think they're paying for," Bruce Silverglade of the Center for Science in the Public Safety told "Good Morning America."
Connecticut tests olive oils for purity and said that it found some that were up to 90 percent soybean oil. Tests show off-brands from discount stores are the biggest problem.
"Name-brand companies generally have more of a quality control operation," Consumer Reports food safety expert Jean Halloran said. "Some of the products in dollar stores are here today and gone tomorrow."
Products like honey and maple syrup are also among the counterfeit culprits. According to the FDA, producers have been caught adding corn syrup, cane sugar or beet sugar to honey to drop the cost.
Vermont, famous for maple syrup, defended the breakfast staple by sending one counterfeiter to prison for using water to dilute his maple syrup. Overall, however, maple syrup alteration is rare, the FDA reports.
The FDA has had a ban on the "adulteration of food" since the 1938 Federal Food, Drug and Cosmetic Act, but according to Silverglade, common sense concerning price is a good defense against faked foods.
"If a product like a pure maple syrup is priced so low that the differential is so different than other similar competing brands, then you probably should be suspicious. The FDA doesn't have the resources to enforce the law," he said.
Fish is among the most commonly faked foods, the FDA said. An investigation by the Chicago Sun-Times found that sushi labeled as red snapper was actually cheaper, farm-raised tilapia. Consumer Reports tested 23 salmon filets labeled wild and found 13 of them were actually farm raised.
"It's definitely a problem if you're thinking you're getting a wild salmon, which can have higher omega-3s and be lower in contaminates like PCBs and in fact you're actually getting the farm raised," Halloran said.
One way to tell wild salmon from farm-raised is the color. Wild salmon stays red after cooking, but farm-raised salmon are fed red pellets to give them their color and the color tends to fade during cooking.
The FDA set up a hot line at its Center for Food Safety and Nutrition at 1-888-723-3366 so consumers can call and check on products they suspect have been altered.