Understanding What are the side effects of animal protein?

October 14, 2025 •

5 min read

According to a 2016 article from Forks Over Knives, unlike plant protein, animal protein contains no dietary fiber, a deficiency that is far more common than not among adults. A deep dive into what are the side effects of animal protein? reveals a complex picture where the source and quantity matter immensely for long-term health outcomes.

Quick Summary

Excessive intake of animal protein, especially from red and processed meats, is linked to higher risks of cardiovascular disease, certain cancers, kidney strain, and metabolic issues. The health effects depend heavily on the specific animal protein source and overall diet. Factors like saturated fat, heme iron, and lack of fiber contribute to adverse outcomes, highlighting the need for varied protein sources.

Key Points

Increased Risk of Heart Disease: High intake of red and processed animal protein can increase bad cholesterol and raise blood pressure due to saturated fat, cholesterol, and TMAO production.
Kidney Strain: Excessive animal protein consumption forces kidneys to work harder to filter waste, potentially worsening kidney function over time, especially in those with pre-existing kidney disease.
Elevated Cancer Risk: Processed meats and high-temperature cooking of red meat have been linked to an increased risk of colorectal and other cancers due to carcinogenic compounds and elevated IGF-1 levels.
Adverse Impact on Bone Health: The higher acid load from animal protein can cause the body to draw calcium from bones, potentially compromising bone density over the long term.
Nutrient Imbalance and Digestive Issues: A diet heavy in animal protein often lacks fiber, leading to digestive problems like constipation and displacing other important nutrient-dense foods.

The conversation around protein often focuses on the quantity required for muscle building and satiety. However, the quality and source of that protein are just as important for overall health. High consumption of animal protein, particularly from red and processed meats, has been associated with several potential side effects that deserve careful consideration. While animal products can be a valuable part of a balanced diet, understanding the risks associated with certain types can help inform healthier food choices.

Cardiovascular Disease Risks

One of the most widely studied side effects of high animal protein intake is its connection to cardiovascular disease (CVD). This link is not solely due to the protein itself but is heavily influenced by accompanying nutrients and metabolic byproducts.

Saturated Fat and Cholesterol: Many animal proteins, especially red meat and high-fat dairy, are rich in saturated fat and cholesterol. High intake of these fats can elevate LDL (bad) cholesterol levels, contributing to atherosclerosis—the buildup of plaque in blood vessels. This increases the risk of heart attacks and strokes. Leaner options like fish and poultry have a neutral or even beneficial effect on heart health compared to red and processed meats.
TMAO Production: The gut microbiome plays a role in heart health. Consuming animal products can alter gut flora, leading to increased production of trimethylamine N-oxide (TMAO). TMAO is a compound that injures the lining of blood vessels, promotes inflammation, and contributes to the formation of cholesterol plaques.
Phosphorus Overload: Animal protein sources often contain high levels of phosphorus. High phosphorus intake triggers the release of Fibroblast Growth Factor 23 (FGF23), a hormone that can be damaging to blood vessels and is associated with a higher risk of heart failure.

Concerns for Kidney Health

The kidneys are responsible for filtering waste products from protein metabolism, primarily nitrogenous waste. A diet excessively high in protein, especially animal protein, can place an increased workload on the kidneys.

Glomerular Hyperfiltration: Excessive protein intake can cause glomerular hyperfiltration, a state where the kidneys’ filtration rate is elevated. Over time, this chronic overworking can lead to kidney damage, particularly in individuals with pre-existing kidney disease or diabetes.
Inflammatory Response: Research suggests that animal protein can trigger an inflammatory response in the kidneys, unlike plant protein. This inflammation contributes to kidney strain and potential long-term damage. Studies have shown that animal protein restriction can improve hyperfiltration and albuminuria in diabetic patients.
Metabolic Acidosis: The higher concentration of sulfur-containing amino acids in animal proteins can create a mild state of metabolic acidosis in the body. This places an added burden on the kidneys to excrete the extra acid. Long-term, this can contribute to faster kidney function decline.

Links to Increased Cancer Risk

Associations between high intake of red and processed meat and an increased risk of certain cancers, particularly colorectal cancer, have been well-documented.

Insulin-like Growth Factor-1 (IGF-1): Animal protein intake can lead to higher levels of IGF-1, a hormone that stimulates cell growth and division. While necessary for healthy development, elevated levels are consistently linked to an increased risk of cancer growth and proliferation.
Carcinogenic Compounds: Cooking meat at high temperatures, such as grilling or frying, can produce heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens. Processing meats with curing, salting, or smoking can also add carcinogenic compounds like N-nitroso compounds (NOCs).
Heme Iron: Heme iron, which is found in high concentrations in red and processed meats, can act as a catalyst to form potent carcinogens and damage DNA through the creation of free radicals.

Impact on Bone Health

While protein is essential for bone health, the type of protein matters. As mentioned, the higher acid load from animal protein's sulfur-containing amino acids can cause the body to pull calcium from the bones to neutralize it. Over time, this can lead to a detrimental effect on bone health and increase the risk of fractures. Some studies have found that populations with higher animal protein and dairy consumption also have a higher incidence of bone fractures.

Other Health Considerations

Beyond the major chronic diseases, there are other noteworthy side effects associated with high animal protein consumption:

Lack of Fiber: A diet heavy in animal products often lacks sufficient fiber, a nutrient crucial for digestive health found only in plants. This deficiency can lead to constipation, bloating, and other digestive issues.
Dehydration: Processing excess protein and nitrogenous waste requires more water, which can lead to increased urination and potential dehydration if fluid intake isn't sufficient.
Nutrient Imbalance: Focusing excessively on animal protein can displace other important nutrients like complex carbohydrates, fruits, and vegetables, leading to potential deficiencies in vitamins, minerals, and antioxidants.

Animal Protein vs. Plant Protein: A Comparison

The table below outlines key differences between animal protein (particularly red and processed meat) and plant protein regarding their potential health impacts.


Feature	Animal Protein (Red/Processed Meat)	Plant Protein (Legumes, Nuts, Seeds)
Associated Health Risks	Increased risk of CVD, certain cancers, kidney issues	Lower risk of heart disease, diabetes, obesity
Nutrient Profile	High in saturated fat, heme iron; no fiber	High in fiber, antioxidants, and phytochemicals; low in saturated fat
Amino Acid Composition	Contains all essential amino acids (considered 'complete')	Many are 'incomplete' individually, but varied sources provide all essential amino acids
Digestibility	Highly digestible (approx. 90-95%)	Slightly lower digestibility (approx. 75-80%) due to cell walls
Metabolic Effects	Can increase IGF-1, TMAO, and metabolic acid load	May improve metabolic health and insulin sensitivity

Conclusion: Finding the Right Balance

While animal protein is a bioavailable source of essential amino acids, focusing excessively on certain types, particularly processed and red meats, can lead to adverse health outcomes. The key lies not in a total elimination of animal protein but in a balanced approach that prioritizes variety and includes a significant portion of plant-based proteins. By reducing consumption of processed meats, limiting red meat, and incorporating more fish, poultry, legumes, and nuts, one can mitigate many of the associated risks. This holistic dietary strategy, emphasizing whole foods and rich nutrient packages, can significantly improve long-term health and well-being. For personalized advice, a consultation with a healthcare professional or registered dietitian is recommended.

For more information on nutrition for optimal health, consult reputable resources like the UCSF Osher Center for Integrative Health.

Frequently Asked Questions

Not directly, but excessive protein intake, particularly from high-fat animal sources, can lead to weight gain over time if overall calorie intake is too high. A balanced diet is key for long-term weight management.

No, the health effects of animal protein depend on the source and amount. Processed and red meats are most consistently linked to adverse effects, while fish and poultry are generally considered healthier choices.

Excessive protein intake, especially from animal sources, can increase the risk of uric acid stone formation due to an increased acid load on the kidneys. Maintaining adequate hydration is also important to prevent this.

Processed meat contains higher levels of sodium, nitrates, and other preservatives that have been linked to increased health risks, including a higher risk of heart disease and certain cancers.

Some observational studies link higher animal protein intake to higher blood pressure, particularly in Western diets. The effects can vary depending on the specific source and overall dietary pattern.

Yes, a varied diet of plant-based foods like legumes, nuts, seeds, and whole grains can provide all the essential amino acids your body needs. Combining different plant sources throughout the day ensures a complete protein intake.

TMAO (trimethylamine N-oxide) is a substance produced by gut bacteria after consuming animal products. It is linked to inflammation and plaque formation in blood vessels, increasing cardiovascular risk.