So you want to add a post-workout protein smoothie or shake to your routine. That’s a good idea: Consuming protein after exercising has been shown to help build muscle mass and strength. But all protein powders aren’t created equal. They are derived from a huge variety of sources, which can have a range of (positive and negative) effects on the body, and sometimes contain not-so-healthy additives. So how do you know which one is right for you when you’re staring down hundreds at the store or online?

For starters, there are two main types: those made from dairy proteins, and those made from plant-derived proteins. Whey and casein are the two dairy proteins that are separated from milk as cheese is made. Like all animal proteins, they are complete proteins, which means they contain all nine essential amino acids. Plant-based powders, on the other hand, are incomplete and must be combined to serve as a complete protein source. You’re likely to come across these sources and blends of them: soy, brown rice, peas and other legumes, wheat, chia seeds, pumpkin seeds, hemp, spirulina, and sunflower seeds.

Armed with that basic knowledge, we asked registered dietitian and nutritionist Amy Shapiro, MS, RD, CDN, founder of New York City–based Real Nutrition, to talk us through the finer points of choosing a protein powder. “If you don’t know to look for a particular type, then they all will look the same to you,” she says. “And that aisle can be very overwhelming.” Here, she weighs in on the types of protein, their benefits, and any potential downsides, and explains how to read labels to pick the best one on the shelf for you.

I’m wondering if I really need extra post-workout protein. Do you recommend protein powders for the average woman’s diet and routine?

I think it is a good idea for most people to have a little extra protein after a workout to prevent the body from using its own muscle tissue for energy and to promote muscle synthesis and repair. It’s more important with weight training than cardio; however, the research here is still a bit weak. Protein also refuels muscles after exercise and assists in recovery, enabling performance to continue in future workouts.

Protein shakes also can benefit you by helping to keep the body in muscle protein balance, control weight (protein takes the body a while to digest), curb appetite, maintain a healthy immune system, and support digestive health.

I recommend choosing whole foods instead of protein shakes when possible. This allows for less processing, clean sources, and often more satisfaction, as people like to chew their food and end up feeling more sated that way. I will recommend protein shakes or smoothies for vegans who are trying to get more protein into their diets, clients on the run, on hot days, and of course for convenience.

When you’re choosing a protein powder, what are the pros and cons of whey-based ones over plant-based ones, aside from the fact that whey protein comes from an animal source?

Plant-based protein often includes many other vitamins, minerals, nutrients, and antioxidants because plants, in general, are full of these goodies. They also contain fiber and digestive enzymes that ease digestion and absorption. However, they tend to be more expensive, and the serving size may have to be larger to get equal amounts of protein compared with animal products.

Whey-based protein may be lacking in nutrient density since it comes from milk. It also can be difficult to digest and absorb for some people. However, because it is a complete protein, there’s no need to supplement it with other forms. You’ll likely receive a higher amount of protein per serving and, depending on the brand, these may be less expensive and more available than plant-based protein.

I’m seeing subcategories of whey protein: concentrate, isolate, and hydrolysate. Which kind is for me, and which are for the hard-core weight lifters?

The average woman will likely encounter whey protein in a concentrate form as that is what is most common. That said, with collagen peptides becoming more popular, you may come across those, too. They are a very absorbable form of protein as they are broken down into peptides for efficient use and ease of digestion.

Anyone using a protein powder and a general supplement should look at the nutrition label to make sure it has protein and limited carbs and sugar. The label should say which type of whey protein is in the powder or if it’s a combination.

The type of protein you choose depends on your goals and knowledge. Studies have found that supplementing weight training with whey protein subcategories causes a greater gain in muscle mass. If you are looking to put on muscle and want quick absorption and low carbs, then hydrolosate or isolate are for you. If you are looking for long-term satiety, casein protein is going to be your number-one choice. If you are just looking to supplement and feel good, then concentrate might be for you.

What do you look for on the label for plant proteins?

The only complete protein that is plant-based is soy protein. It’s a great option if you are looking for a vegan, nutrient-rich protein source. Otherwise, the best way to get a complete protein is to mix or purchase a mix of brown rice protein (which is gluten-free, low in carbs and fats, easily digestible, and high in many essential amino acids but low in lysine) and pea protein (which is high in lysine and branched-chain amino acids).

I recommend that my clients look for protein powders with at least one source from the methionine-rich camp (hemp, chia, soy) and one from the lysine- and leucine-rich camp (wheat, quinoa, oat, brown rice). Certain protein powders that focus on superfoods are trendy, and I don’t tell clients to stay away from them, but they’re not necessary, either.

Aside from added sugars, are there other things you want to ensure aren’t in your protein powder or bar?

Depending on the person, I may recommend staying away from casein and whey protein concentrate because of the lactose, which can cause bloating and flatulence. Skim milk powders and milk solids can also find their way into ingredient lists because they are less expensive bulking agents; they may also cause GI distress. In addition to casein and lactose, egg, soy, and wheat are common allergens you may want to look out for.

Dextrin and glucose are fillers that can raise glycemic load and insulin levels, and can contribute to fat storage, which is usually not what one is looking for when consuming protein powders. Watch out for vegetable oils and fats derived from hydrogenated sources that have trans fats, as these are not health promoting. Keep an eye out for thickeners, added fibers, and gums, which may even be natural but can cause bloating, constipation, and general discomfort if consumed without enough fluid.

Artificial sweeteners, including sucralose, aspartame, and even all-natural sugar alcohols, can cause gas, bloating, and diarrhea in some people. These allow for protein powders or bars to taste very sweet but to have a low carb count, so they are attractive to many people. However, they can cause a lot of GI discomfort and also can lead to sweet cravings later on in the day.