Are there negative effects of protein shakes? What you need to know about the risks

October 20, 2025 •

5 min read

According to the Clean Label Project, a 2018 study found nearly 50% of tested protein powders contained potentially harmful heavy metals, with organic and plant-based versions showing the highest levels. This raises a critical question for many consumers: are there negative effects of protein shakes?

Quick Summary

Protein shakes can cause digestive distress, and excessive, long-term use can strain the kidneys and liver. Many products also contain contaminants like heavy metals and unnecessary additives. Relying on shakes may displace nutrient-dense whole foods and contribute to unwanted weight gain if not managed correctly.

Key Points

Digestive Distress: Many protein shakes, especially dairy-based ones, can cause bloating, gas, or cramps, particularly for those with lactose intolerance or sensitivity to artificial sweeteners.
Kidney and Liver Strain: Excessive, long-term protein intake can put extra strain on the kidneys and liver, which is especially concerning for individuals with pre-existing organ conditions.
Heavy Metal Contamination: A lack of robust regulation means some protein powders may contain dangerous heavy metals like arsenic, lead, and cadmium, which can accumulate in the body over time.
Nutrient Displacement: Relying heavily on shakes can cause individuals to miss out on the rich array of vitamins, minerals, and fiber found in whole foods, potentially leading to deficiencies.
Unintended Weight Gain: Though often associated with weight loss, shakes add calories, and if not balanced with activity, this can lead to a calorie surplus and unwanted weight gain.
Additives and Fillers: Many products include artificial sweeteners and thickeners that offer no nutritional value and can cause digestive issues or other adverse reactions.

Protein shakes have become a staple for many fitness enthusiasts, athletes, and individuals looking to boost their daily protein intake. Marketed as a convenient and efficient way to build muscle, aid recovery, and support weight management, these supplements are widely consumed. However, the convenience and potential benefits don't tell the whole story. As with any supplement, understanding the potential drawbacks is essential for informed and safe consumption.

Potential Side Effects and Digestive Issues

One of the most immediate and common complaints from protein shake users involves gastrointestinal distress. Symptoms can range from mild discomfort to more severe issues, depending on the type of protein and individual tolerance.

Digestive upset and the type of protein

Lactose Intolerance: Many whey and casein protein powders are dairy-based and contain lactose. For individuals with lactose intolerance, consuming these shakes can lead to bloating, gas, stomach cramps, and diarrhea. Switching to a hydrolyzed whey protein isolate or a plant-based alternative can often alleviate these symptoms.
Too much, too fast: Your body can only digest a certain amount of protein at one time. Consuming large scoops or chugging a shake too quickly can overwhelm the digestive system, causing discomfort. The digestive process can also slow down during and immediately after intense exercise, making a shake chugged right after a workout more likely to cause issues.
Fillers and sweeteners: Many commercially flavored protein powders contain artificial sweeteners (like sucralose and aspartame), sugar alcohols (like sorbitol), and thickeners (like xanthan gum). These additives can disrupt the gut microbiome and trigger digestive issues, even in people without a diagnosed intolerance.

Long-Term Effects on Kidneys and Liver

The human body is remarkably efficient at processing protein, but excessive intake over a prolonged period can put a strain on vital organs, particularly the kidneys and liver.

Kidney function and high protein

For individuals with healthy kidneys, a high-protein diet is unlikely to cause damage. However, this is not the case for people with pre-existing kidney disease. In these individuals, excessive protein can accelerate the decline of kidney function. This is because the kidneys must work harder to filter out protein metabolites like urea. A balanced approach is key, and those with any kidney conditions should consult a healthcare professional before increasing protein intake.

Liver and metabolic health

Similarly, excessive protein, especially without sufficient exercise, can put pressure on the liver to process the extra protein. While the liver can generally handle this, long-term overburdening is a theoretical risk, particularly for those with underlying liver disease. Some studies have also linked high-protein diets, often heavy in animal protein, with elevated levels of uric acid, which can exacerbate conditions like gout.

Contaminants and Lack of Regulation

One of the most concerning aspects of protein shakes is the lack of strict regulation for dietary supplements by bodies like the FDA. This means manufacturers are largely responsible for evaluating the safety and labeling of their products. This self-regulation can lead to serious quality control issues.

Heavy metals and other toxins

Numerous studies have revealed the presence of toxic substances in protein powders, including heavy metals like arsenic, cadmium, lead, and mercury. These contaminants can leach into supplements from contaminated soil and water sources used to grow plant-based protein or from the manufacturing process itself. Long-term, low-dose exposure to these metals can lead to a buildup in the body, causing potential harm to neurological and reproductive health, as well as an increased risk of kidney disease and cancer.

Added fillers and artificial ingredients

Beyond heavy metals, many products contain a cocktail of additives that can be problematic. These include artificial flavorings, sweeteners, and fillers that have no nutritional value and may cause digestive discomfort or other adverse health effects. The presence of these inexpensive fillers can also mean the product contains less actual protein than advertised.

Unintended Weight Gain

While protein shakes are often used for weight loss, they can contribute to weight gain if not used mindfully. This occurs when the extra calories from the shakes, combined with regular food intake, lead to a calorie surplus. Some products, particularly mass gainers, are intentionally formulated with high calories and added sugars to help users bulk up, which can cause an unhealthy spike in blood sugar. It is crucial to monitor overall caloric intake when using shakes to avoid unwanted weight gain.

The Problem of Nutrient Displacement

Over-reliance on protein shakes can cause a person to neglect the benefits of whole foods. Protein powders are isolated nutrients, lacking the full spectrum of vitamins, minerals, and dietary fiber found in natural protein sources like chicken, fish, eggs, beans, and nuts. Replacing meals with shakes can lead to nutrient deficiencies and can even cause constipation if fiber intake is too low. Prioritizing a varied diet rich in whole foods is always the healthier approach.

Comparison: Protein Shakes vs. Whole Food Protein


Feature	Protein Shakes (Supplements)	Whole Food Protein Sources (e.g., meat, eggs, legumes)
Convenience	High. Quick to mix and consume on-the-go.	Low to moderate. Requires preparation and cooking.
Micronutrients	Minimal. Many lack the vitamins and minerals found naturally in whole foods.	High. Packed with essential vitamins, minerals, and other beneficial compounds.
Digestibility	Can be very fast (whey) or slow (casein). May cause issues for those with intolerances or sensitivities.	Slower, more gradual absorption. Less likely to cause digestive distress for most people.
Cost	Can be expensive over time, depending on the brand and quality.	Often more affordable per gram of protein.
Risk of Contaminants	Variable, due to lack of regulation. High risk for contamination with heavy metals, pesticides, or other toxins.	Very low, as whole foods are subject to more stringent food safety standards.
Satiety	Less satiating than solid food, which can lead to eating more later.	More satiating, helping to control appetite and prevent overeating.

Conclusion: Navigating Protein Shakes Safely

While protein shakes offer a convenient and targeted way to increase protein intake, particularly for athletes or those with specific needs, it is clear that they are not without potential downsides. The negative effects range from immediate digestive discomfort to long-term concerns regarding kidney and liver strain, and the hidden danger of contaminants. The best strategy is to prioritize whole food protein sources and use supplements as a supplement, not a replacement. Always choose high-quality brands that offer third-party testing certifications to minimize exposure to heavy metals and other toxins. Ultimately, listen to your body, understand your nutritional goals, and remember that real food provides a more comprehensive nutrient profile for long-term health.

For more information on the risks of dietary supplements, you can consult reliable sources such as this article from Harvard Health.

Frequently Asked Questions

Yes, protein shakes can cause digestive issues. Diarrhea can be caused by lactose in dairy-based proteins or by artificial sweeteners. Constipation can occur if you consume too much protein without enough fiber and water.

For most healthy individuals, moderate protein shake consumption is unlikely to harm the kidneys. However, excessive intake can pose a risk for people with pre-existing kidney disease, as it increases the filtering workload on the kidneys.

Many protein powders have been found to contain heavy metals such as arsenic, cadmium, lead, and mercury, due to minimal regulatory oversight. It is important to choose brands that conduct and provide results from third-party testing to ensure safety.

Yes, if they add too many calories to your diet. Weight gain depends on your total caloric intake. If protein shakes create a caloric surplus, you can gain weight, especially if they are high in added sugars.

Not necessarily. While plant-based options are good for those with dairy allergies, studies have shown that some organic and plant-based protein powders actually have higher levels of heavy metal contamination compared to dairy-based alternatives.

Prioritizing whole food sources of protein is generally recommended. Whole foods offer a full spectrum of nutrients, including vitamins, minerals, and fiber, that are often missing from isolated protein powders.

Most experts recommend limiting intake to one to three shakes per day to supplement, not replace, a healthy diet. The exact number depends on your individual protein needs, activity level, and the rest of your diet.