Meal replacement powders, AKA MRP's, are blends of protein, carbohydrates, fat, vitamins, minerals and sometimes other added supplements (e.g., ribose, creatine, etc). Some claim to deliver precise ratios of protein and specific amino acids for recovery and growth, while others claim to be packaged nutrients that can be blended for a quick meal.
Most MRP's available offer very similar macro- and micronutrient profiles, so with blenders on hand and MRP powder strewn across my kitchen, I have put my mind (and mouth) on the line to sort through the common ingredients contained in MRP's and provide an in depth look at these packaged "meals."
Protein usually appears as the first ingredient, or group of ingredients, in most MRP's. As with any food, MRPs must also follow the labeling rule that the first ingredient listed is the one that is most abundant in the product.
This is the reason that companies put all of the proteins contained in the product in parenthesis and give them a fancy name (so protein can be listed as the first ingredient on the label). If any of the proteins were listed individually, most products would have to list them lower on the ingredient list.
You might think that the type of protein found in a particular MRP would be an important consideration when choosing between different products. The fact of the matter is that when the different protein concentrates/isolates are compared on a gram per gram (of protein) basis, there is really not a whole lot of difference between them in terms of what they will do for you when you eat them.
Right now, whey protein is considered by many athletes to be "superior" to other proteins for supposed benefits like boosting immune function - but these claims are based on test-tube studies and not on feeding studies in humans. As long as your MRP contains a blend of complete proteins you will be OK.
Although since many of you are curious about the different forms of protein, here's a very brief synopsis of a few.
Before getting into some different components of whey, it's important to first describe whey protein itself. Whey protein is taken directly from cheese production (think Little Miss Muffet, eating her curds and whey).
The product is clarified, to remove the most or all of the fat and lactose, and dried into a white powder. The extent of isolation and purification then determines what type of whey is produced. This article won't get into the fancy, scientific mumbo jumbo of cross flow, ultra-filtered, once filtered, infinitely filtered, etc.
Whey Protein Concentrate (WPC)
WPC is one of the cheapest methods of production, leaving some other non-protein components in the powder in addition to protein itself. When compared to more expensive forms of whey protein, it contains a little less protein per gram, which is why it is less expensive, but this does not make it a useless form of protein.
Whey Protein Isolate (WPI)
WPI is more expensive because gram for gram, it contains more protein than other forms of whey. It also has higher levels of some immunoglobins and certain amino acids than other forms of whey.
Casein protein is commonly found in dairy products (think lumps in cottage cheese). Casein is actually the curds part of the separated cheese (Little Miss Muffet apparently wasn't happy referring to her curds as casein, she preferred to eat her curds and whey because it sounded catchier in the famous children's poem).
Because casein is highest in dairy products, it's not surprising that it also contains more lactose than whey protein.
Protein Hydrolysates (all inclusive for all hydrolyzed proteins)
Hydrolyzed proteins are ones that have been enzymatically broken down. This process makes the protein more easily digestible because there is less work for your GI tract. Proponents of this form of protein promote its ability to be absorbed more rapidly (because it is essentially pre-digested).
Eggs have been touted by some as the perfect food; they are not only inexpensive, but they are complete proteins, meaning they contain all essential amino acids in adequate ratios to promote growth. Therefore, many manufacturers include egg protein in their MRP's claiming it has the most complete amino acid profile.
The selling point for many MRP's is how quickly (or slowly) the different proteins are absorbed. It is in fact true that after a 12-hour overnight fast, whey protein, when given as the sole source of energy, is absorbed more rapidly than casein protein.
However, considering that fasting for 12-hours and then only eating pure whey or pure casein is rather uncommon, the practicality of this claim may not hold much clout in terms of the "real world" applicability. This is particularly true in the case of MRP's because there is a grocery list of ingredients alongside protein that also affect the rate of digestion.
An additional consideration when choosing a MRP is the combination of other ingredients in the mix. If your MRP were composed of "pure protein" with no other ingredients, it would taste exceedingly horrendous. That's why manufacturers have to add flavors, sweeteners, thickening agents, etc. - to make this stuff enjoyable. Here are two of the common additions:
Maltodextrin is a common glucose polymer (chain of glucose molecules) that is one of the more prevalent carbohydrates added to MRP's. It is relatively inexpensive, causes a rapid rise in blood sugar (recommended post-workout) and adds sweetness (i.e. flavor) to MRP's.
Essential Fatty Acids (EFA's)
Essential fatty acids are one of the more recent additions to MRP's. They are often added as sunflower oil or flax seed. EFA's are typically included to slow the rapid rise in blood sugar following certain meals and are added for their known health benefits.
There are also a few ingredients you need to keep an eye out for and avoid like the plague. First and foremost is hydrogenated or partially hydrogenated oil. Why anyone in their right mind would want to deliberately add unhealthy fat to their diet is beyond me. Similarly, high fructose corn syrup is a cheap, sweetener used in many products. Unfortunately, it has also made its way into too many MRP's.
MRP's should not be the mainstay of anyone's diet, no matter who you are; however, they can definitely make a nice addition for convenience alone - and many of them actually taste great. Remember to read the labels and pick the product that best suits your needs in the categories of taste, convenience, and value.
When choosing a MRP, taste may arguably be the best indicator of how useful the MRP may be. If you have you hold your nose, jump up and down, and almost pass-out just to drink your shake, it's not going to have much benefit due to lack of compliance when taking it.
On the contrary, if you have a product that is enjoyable and contains most of the positive aforementioned ingredients discussed, you're in luck. So if MRP's aren't the cornerstone of your supplement regimen, I suggest you give them a try.
Blend up some frozen fruit with your chosen product and you have a low-fat, high protein meal that's chock full of nutrients.