The most common kind of protein found in fitness shakes is whey protein, which is considered easily digestible. Some companies claim to have developed powders that directly transfer the protein to your muscles. While not technically dangerous if taken as directed, protein shakes made with whey protein can cause gas, nausea and bloating.
Kidney or Liver Damage
The biggest danger of protein shakes is damage the kidneys or liver. It is unlikely that even one or two protein shakes a day will harm your body, but any more than that consumed consistently over time forces your kidneys and liver to work overtime.
Since the protein being ingested is either plant or soy protein (both harder to digest than animal protein), the body must work harder to dispose of any leftover protein in the body. Since the shakes may lack all of the amino acids and other components that make animal protein more digestible, the liver and kidney will eventually struggle.
Because protein supplements are highly processed, they may contain protein toxins, which, when present in the body support the bad bacteria found in your gastrointestinal tract. This bacteria uses the protein toxins to create more protein toxins, which in turn can create gas or bloating. Over time, the possibility exists for these symptoms to worsen.
Ignoring Other Nutrients
When choosing to build muscle, fitness buffs may focus too much on adding protein to their diets while forgetting that fiber, dairy, water and even sugar are crucial to the body's function. It is generally recommended that if you are using protein shakes as a meal replacement, you should eat at least one well-balanced "real" meal daily.
Long-term use of protein shakes can lead to kidney or liver conditions, although it is likely that you will seek treatment before such a condition becomes unmanageable. The rule of thumb for building muscle is to ingest more protein, and, while protein shakes may be an easy way to do this, they are not always the most effective. Since our bodies are designed to better digest animal protein, make sure to continue to consume protein in this form. Protein shakes can help an individual to bulk up, but avoid overuse. If you choose to use protein shakes, use as directed.