(CNN) - Protein powders are expected to be a $7.5 billion industry by 2020, and the products are popular for a wide variety of reasons: Vegetarians might feel that their diets are somewhat lacking, athletes may want to add muscle faster or aim for a competitive edge, and still others might be looking for a quick meal that isn't dripping with grease.
And there's an equally wide variety of products on the market. Here's what you should know about protein powders.
Protein is an important building block for muscle as well as hair, skin and nails. Powders are dehydrated forms from sources such as milk, soy or plants. They're typically mixed with water or other beverages, or they can be added to foods to boost protein content.
Athletes' protein needs can be up to twice those of the average person because of the energy they expend and the process of breaking down, repairing and building muscle. Many vegans also use protein powders in lieu of animal-based sources such as meat, dairy or eggs.
The recommended dietary allowance for protein is about 0.8 grams per kilogram of body weight each day, which translates to 54 grams for a 150-pound person.
However, "I think those estimates are a little conservative," nutritionist and health journalist Lisa Drayer said, "because as you get older, you lose muscle mass, and it's important to consume an adequate amount of protein to preserve muscle mass, even if you're not an athlete." She recommends that the average adult get 20% to 25% of their calories from protein: 100 to 125 grams for a person on a 2,000-calorie diet.
Protein needs vary by the individual; older adults or those recovering from surgery or illness might need more.
Protein powder pros
Convenience is the top benefit protein powders offer, especially for athletes or those looking to supplement their diets. "Even athletes who have some of the highest needs can meet their needs through foods," said Drayer, who also writes about nutrition for CNN. "It's really like, do you want to bring the yogurt and nuts after running a half-marathon, or would you rather have the protein supplement there?"
Similarly, "if you're just low on protein and you just don't have the appetite for a chicken breast for dinner, it's just a nice way to mix into smoothies or oatmeal or baked goods."
As a nutrient, protein is very filling, which can help you avoid overeating later, and it preserves muscle to keep your metabolism running at its peak. Powders might offer a bit of a metabolic advantage if they are low in calories.
Most powders contain whey, soy or casein, high-quality proteins containing all nine essential amino acids that the body can't make on its own.
Protein powder cons
Too much protein -- starting at about 35% of daily calories -- can lead to health issues such as nausea, cramps, fatigue, headaches and bloating. Some experts think it can cause the kidneys to have to work harder, leading to complications for those with existing kidney problems, or increase calcium excretion, causing bone loss. Dehydration is also a risk for those consuming a lot of protein.
Many of these products contain added oils, sugars, probiotics or amino acids. Sugars and oils can mean more calories, potentially leading to weight gain. However, the labels can have unverified claims or be difficult to decode.
"One I saw had brown rice syrup solids. It had 20 grams of sugar: That's 5 teaspoons of sugar," Drayer said. "Clearly, it's not just protein."
Some protein powders may contain unlisted ingredients such as stimulants or even steroids. "Often, consumers are not very discriminating in which ones they use," said Larry Walker, emeritus director of the National Center for Natural Products Research and emeritus professor of pharmacology at the University of Mississippi. "It's more marketing than, really, a careful look at the labels and understanding the product."
Certain plants can absorb heavy metals from the soil that are then passed along in protein powder if not screened well, he said.
"The other things that are added in are just often difficult to gauge, and they may be just ineffective, just a waste of money, but there could be those things that can be dangerous."
How to get the most out of protein powder
A dietitian can help you decide whether protein powder is the best bet for your diet or whether you're getting enough nutrients from food alone. A doctor can keep an eye on potential protein-related health concerns with your kidneys or your calcium intake.
If you add protein to your diet, be sure to add plenty of fluids to head off dehydration. Read product labels and be sure you understand what you're consuming. "If you want protein supplements, you want to look for those things that are protein supplements, from soy or whey or casein or whatever mixtures it might be," Walker advised. "But stay away from the extraneous ingredients."
He also says consumers should be wary of hype marketing claims such as rapidly gaining muscle or losing weight. "Look for good-quality products or well-established companies in the nutrition field, and use these in moderation."
Most people's protein needs can simply be met through food, Drayer says: One container of Greek yogurt and a handful of almonds contains 24 grams, the same as one serving of some protein supplements. She also recommends low-fat milk powder as a convenient, inexpensive alternative to protein powders.
"It's still important to consume whole foods, because they provide a variety of nutrients as well as fiber," Drayer said. Protein powders are "really meant as a supplement."
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