While protein bars are an efficient way to get in some protein, the quality of that protein may be questionable, according to recent research. A study published in the journal Scientific Reports in March analyzed the protein quality of 1,641 protein bars using data from the website OpenFoodFacts.org—and discovered low protein nutritional quality across the bars. That may hinder how much protein your body is actually able to absorb and use.

Protein bars with the highest and lowest protein quality

To evaluate the quality of the protein in the bars, the researchers mimicked the digestion process in lab simulations to determine the protein digestibility, and therefore its quality.

The researchers divided the protein bars into four categories of commonly used proteins: (A) plant only (pea and rice); (B) animal only (milk proteins); (C) mix of animal (milk and egg) and plant (soy); (D) mix of animal (milk and collagen) and plant (soy).

While 81% of the bars had sufficient protein quantities to be labeled as “high in protein,” protein digestibility could be low, ranging from 86% to as low as 47%.

The study authors hypothesized that the degradation in protein quality was likely due to the addition of ingredients like “lower-nutritional-quality proteins (such as collagen) and of other ingredients such as carbohydrates, fats and fibers, that might deteriorate the bioaccessibility of essential amino acids.”

They found that the bars with the highest protein quality contained only animal-based proteins in the form of whey protein concentrate and milk protein (casein) concentrate, which are both proteins found in milk. The bars with the lowest protein quality were the entirely plant-based bars, with their protein sources coming from pea protein isolate and rice protein isolate. They also observed that animal-based protein bars had higher protein and fiber content, and lower calories, fat, carbohydrate, and sugar content.

The study authors also caution more scrutiny of protein bars that contain added collagen. While that ingredient may boost the overall protein content, collagen is mostly made of non-essential amino acids that may not contribute to the protein you typically need for muscle growth and repair.

When the findings revealing lower protein quality are taken in conjunction with the amount of added ingredients in protein bars—which are often considered to be ultra-processed foods—the researchers warn that advertising could be misleading.

“It has been proposed that the sometimes misleading advertisement using phrases like ‘high protein’ and ‘rich in protein’ depicted on packaging of protein bars could shift consumer perception to falsely make a ‘healthier’ food choice,” they wrote in the study.

With that in mind, the researchers advise that protein bars are consumed as a part of a “complete diet,” favoring whole foods.

“We think that these results raise the question of the nature of the true protein nutritional quality of high protein products and generate the need for more data to reveal the relationship between protein sources, the effect of additional ingredients and protein nutritional quality of protein-associated food products,” they concluded.

Experts have indicated that most people likely don’t need to supplement their protein intake with products like bars or powders, anyway.

“If you’re meeting your caloric needs … you’re meeting your protein needs,” registered dietitian Abbey Sharp told Fortune. 

She added that the only people who are protein deficient are people who are malnourished or older adults with reduced appetites and struggling to eat enough calories. As long as you eat enough during the day, you are likely meeting or exceeding our protein needs, she said—including vegans and vegetarians, as long as they are eating a diverse array of nutrient-dense plant-based foods like edamame, lentils, and whole grains.

For more on protein:

• Here’s exactly how much protein you need based on your workout routine
• You might be overdoing it on protein and not getting enough of another vital nutrient, dietitians say
• How much protein do you need in a day? Figuring out the right amount for you
• Using one of the best protein powders is a way to add variety into your diet and protein sources