Do protein drinks have side effects? An expert-backed guide

January 6, 2026 •

3 min read

According to a report by the Clean Label Project, many popular protein powders contained detectable levels of heavy metals like lead, arsenic, and cadmium, highlighting a key concern beyond nutritional intake alone. While protein drinks can be a convenient supplement, consumers should be aware of various potential side effects, particularly when intake is excessive or the product quality is poor.

Quick Summary

This guide examines potential side effects of protein drinks, including digestive distress, kidney and liver strain with excessive use, and the risk of contamination in unregulated products. It details how to minimize risks and make safer choices.

Key Points

Digestive Distress: Many experience bloating, gas, or diarrhea, often caused by lactose in dairy-based protein or excessive intake.
Kidney Strain: Excessive, long-term protein consumption can increase the workload on the kidneys, especially for those with existing kidney conditions.
Contamination Risk: Due to limited FDA regulation, some protein powders have been found to contain heavy metals, pesticides, and other contaminants.
Nutrient Imbalance: Relying too heavily on supplements can displace whole foods rich in fiber, vitamins, and minerals, leading to nutritional deficiencies.
Weight Gain: Excess calories from protein drinks can lead to weight gain if not balanced with sufficient physical activity.
Allergic Reactions: Individuals with a dairy allergy may experience severe allergic reactions, making non-dairy alternatives essential.
Acne and Inflammation: Some studies suggest links between excessive whey protein consumption and increased acne or inflammation.

Protein drinks and powders have become staples for many looking to build muscle, manage weight, or supplement their diet. Made from sources like whey, casein, soy, and pea, these supplements offer a concentrated dose of protein. However, excessive consumption, underlying health conditions, and product quality can lead to a variety of unwanted side effects.

Potential digestive issues from protein drinks

Digestive discomfort is one of the most commonly reported side effects, especially with dairy-based protein powders like whey and casein.

Lactose intolerance and dairy-based proteins

Many whey protein concentrates contain lactose, a milk sugar that a large portion of the global population struggles to digest due to a lactase enzyme deficiency. This can lead to symptoms such as:

Bloating
Gas
Stomach cramps
Diarrhea

Those with lactose sensitivity can often tolerate whey protein isolate, which contains minimal lactose, or can opt for plant-based alternatives.

Other gastrointestinal side effects

Even without lactose intolerance, protein shakes can upset the stomach. Excessive protein intake, a low-fiber diet, or drinking a shake too quickly post-workout can all contribute to digestive distress. Some plant-based powders, such as pea protein, may also cause bloating due to high fiber or FODMAP content. The fermentation of amino acids from high-protein diets in the colon can disrupt the gut microbiome and produce harmful metabolites.

Impact of excessive protein on the kidneys and liver

While healthy kidneys can typically handle an increased protein load, consistently consuming more protein than the body needs puts additional strain on these organs, particularly for individuals with pre-existing conditions.

Kidney strain: When the body processes protein, it produces nitrogenous waste products like urea. The kidneys must work harder to filter and excrete this waste. Long-term, excessive intake may worsen function in those with pre-existing kidney disease. A high-protein diet may also raise calcium and oxalate levels in the urine, increasing the risk of kidney stones in susceptible individuals.
Liver workload: Similarly, the liver's workload increases when processing excess protein. While evidence is mixed for healthy individuals, people with severe liver disease must exercise caution, as a high-protein diet can lead to elevated blood ammonia levels.

The risk of contamination in supplements

Since protein powders are regulated as dietary supplements, the FDA's oversight is not as stringent as it is for food and drugs. This can lead to potential contamination issues.

A study by the Clean Label Project found that some popular protein powders contained heavy metals, such as lead, arsenic, cadmium, and mercury.
Other potential contaminants include bisphenol-A (BPA) from plastic packaging, pesticides, and unlisted additives.

Consumers should choose third-party tested products (e.g., NSF Certified for Sport) from reputable manufacturers to minimize exposure risks.

How to mitigate side effects

Comparison of protein sources and side effects


Feature	Whey Protein	Casein Protein	Plant-Based Protein (Soy, Pea, Hemp)
Source	Dairy (fast absorption)	Dairy (slow absorption)	Legumes, seeds, rice
Common Side Effects	Bloating, gas, diarrhea (especially with concentrate)	Bloating, gas, digestive discomfort (due to slow digestion)	Gas, bloating, stomach cramps (often milder)
Intolerance Risk	High for lactose-sensitive individuals	High for lactose-sensitive individuals	Low; good for dairy allergies/intolerances
Contaminants	Potential risk in some brands; choose third-party tested	Potential risk in some brands; choose third-party tested	Potential risk in some brands; choose third-party tested
Best For	Post-workout recovery	Overnight protein drip	Lactose intolerant or vegan diets

Conclusion

For most healthy adults, protein drinks are safe when consumed in moderation and as part of a balanced diet. However, risks increase with excessive intake, reliance on supplements over whole foods, or for individuals with pre-existing health issues like kidney or liver disease. Common side effects, such as digestive problems, are often tied to dairy sensitivity or excessive amounts, which can be managed by adjusting intake or switching to a different protein type. It is crucial to select third-party tested brands to avoid potential contaminants and prioritize whole food sources of protein to ensure a well-rounded nutrient intake. Always consult a healthcare provider or dietitian before making significant changes to your diet, especially if you have underlying health conditions.

For more information on protein intake guidelines, consult the National Institutes of Health. [https://pmc.ncbi.nlm.nih.gov/articles/PMC4424780/]

Frequently Asked Questions

Protein drinks are generally safe for most healthy adults in moderation. However, people with existing kidney or liver disease, allergies, or lactose intolerance should exercise caution and consult a healthcare professional before use.

For healthy individuals, moderate protein intake from supplements does not typically cause kidney damage. However, those with pre-existing kidney disease may experience a worsened condition with a high-protein diet, and excessive long-term use can strain healthy kidneys.

Digestive problems are often caused by lactose intolerance, especially with whey protein concentrate. Other factors include excessive intake, a lack of dietary fiber, artificial sweeteners, or drinking a shake too quickly after a strenuous workout.

To minimize the risk of heavy metal contamination, choose products that are independently tested and certified by third-party organizations such as NSF Certified for Sport or the Clean Label Project.

Protein shakes contain calories. If you consume more calories than your body burns, including those from protein drinks, you can gain weight. This risk is higher with supplements containing high levels of added sugar and other calorie-dense ingredients.

For those with dairy allergies or lactose intolerance, plant-based proteins from sources like soy, pea, or hemp are a safer alternative to dairy-based whey. They often cause fewer digestive issues but can also contain contaminants, so choosing a tested brand is still important.

To improve gut tolerance, try a hydrolyzed protein formula, add digestive enzymes, ensure adequate hydration, and increase your fiber intake from whole foods. Consuming a protein shake at least 30 minutes after a workout can also help.