Side effects of Muscle Milk include weight gain, bloating, gas, diarrhea and constipation, and high doses can lead to vitamin and heavy metal toxicity. Muscle Cultivation explains that since every serving contains about 310 calories, weight gain from excess intake occurs if those additional calories are not offset. Muscle Milk also contains crystalline fructose, a sweetener that can cause bloating and gas, and diarrhea or constipation depending on the person.
Muscle Milk has high levels of the heavy metals cadmium, arsenic, mercury and lead, and according to Consumer Reports, the levels are some of the highest of any of the protein powders on the market. The Agency for Toxic Substances and Disease Registry lists arsenic, lead and mercury as the top three most hazardous toxic waste substances. Metal toxicity can cause organ failure and brain damage. It takes the body up to 20 years to eliminate cadmium, which also causes kidney damage.
The Vitamin Magazine explains that Muscle Milk also contains added vitamins, so consuming more than the recommended amount can cause vitamin toxicity. Vitamins A and D are particularly worrisome because they are fat soluble, which means that the body does not flush out or absorb excess quantities of them. Toxicity of this kind leads to headaches, nausea and vomiting.