What are the cons of plant-based protein?

November 5, 2025 •

4 min read

While plant-based proteins have soared in popularity for their ethical and environmental benefits, a 2022 review in The Open Biotechnology Journal highlights that anti-nutritional factors are widespread in plant-based foods. Understanding the cons of plant-based protein is crucial for maintaining a nutritionally balanced diet, especially for those who rely on them as a primary protein source.

Quick Summary

This article examines the drawbacks of plant-based protein sources, including lower digestibility, incomplete amino acid profiles, potential deficiencies in key nutrients like vitamin B12 and iron, and the effects of anti-nutrients. The text covers how to mitigate these issues for a balanced, plant-focused diet.

Key Points

Incomplete Protein Profile: Most plant proteins lack one or more essential amino acids, requiring strategic food combining for a complete profile.
Lower Digestibility: Plant proteins are generally absorbed less efficiently by the body compared to animal proteins.
Presence of Anti-Nutrients: Compounds like phytates and lectins in plant foods can inhibit the absorption of essential minerals like iron and zinc.
Risk of Nutrient Deficiencies: Those on strict plant-based diets may face a higher risk of deficiencies in Vitamin B12, iron, and zinc, which are more readily available in animal products.
Varied Digestibility: Plant protein digestion varies significantly by source, with some, like pea protein, having higher absorption rates than others.
Requires Intentional Planning: Achieving a balanced intake of all essential amino acids and micronutrients requires more mindful meal planning than a diet including animal products.
Can be More Costly: While staples like beans are cheap, specialized plant-based protein powders and meat alternatives can be expensive.
Culinary Challenges: Some individuals may dislike the taste or texture of certain plant protein sources, and processed alternatives can be high in sodium.

Incomplete Amino Acid Profile and Lower Bioavailability

One of the most common issues with solely relying on plant-based protein is its amino acid profile. Unlike most animal proteins, which are considered 'complete' because they contain all nine essential amino acids in sufficient quantities, many plant proteins are 'incomplete'. Grains, for example, are often low in the essential amino acid lysine, while legumes can be low in methionine. While combining different plant sources, like beans and rice, can create a complete protein over the course of a day, it requires careful planning to ensure nutritional needs are consistently met.

Additionally, the bioavailability of plant protein is often lower than animal protein. This means the body does not absorb and utilize plant-based protein as efficiently. Factors like fibrous cell walls in plants can reduce the rate of digestion, though for most individuals, the overall difference is minor if daily protein requirements are adequately exceeded. However, individuals with barely sufficient protein intake might need to consume larger quantities of plant protein to compensate.

The Impact of Anti-Nutrients

Another significant drawback comes from compounds known as anti-nutrients, which are naturally present in many plants and can interfere with nutrient absorption. Key anti-nutrients include:

Phytates: Found in grains, nuts, and seeds, phytates bind to minerals like iron, zinc, and calcium, reducing their absorption.
Lectins: Present in legumes and grains, certain lectins can cause gastrointestinal discomfort or damage the intestinal lining in sensitive individuals, though most are denatured by proper cooking.
Tannins: Found in legumes and other plant foods, tannins can inhibit the absorption of iron and other minerals.

Proper food preparation methods, such as soaking, sprouting, and fermentation, can significantly reduce the concentration of these anti-nutrients. However, the presence of these compounds means that simply substituting animal protein with an equal gram amount of plant protein might not yield the same nutritional results for certain micronutrients.

Potential for Specific Nutrient Deficiencies

Solely relying on plant-based protein can increase the risk of specific nutrient deficiencies, particularly when not combined with supplementation or fortified foods. Some critical nutrients primarily found in animal products are less bioavailable or absent in plant sources.

Vitamin B12: This vitamin is crucial for neurological function and red blood cell production but is not naturally found in plant foods. Vegans must rely on supplements or fortified foods to avoid severe deficiency.
Iron: While iron is found in many plant foods (non-heme iron), it is less easily absorbed than the heme iron found in animal products. Phytates and tannins further inhibit this absorption, making it a concern for those with insufficient intake.
Zinc: Similarly, zinc absorption is inhibited by phytates in grains and legumes. A plant-based diet may require careful planning or supplementation to ensure adequate intake of this mineral, which is vital for immune function.
Omega-3 Fatty Acids (DHA/EPA): While ALA omega-3s are found in some plant sources (flaxseeds, walnuts), the conversion to the more crucial DHA and EPA forms is inefficient. Supplementation or fortified foods are often necessary.

Comparison of Plant Protein vs. Animal Protein


Feature	Plant-Based Protein	Animal-Based Protein
Amino Acid Profile	Often incomplete; requires combining sources for all essential amino acids.	Complete; contains all essential amino acids in sufficient amounts.
Digestibility	Lower digestibility and absorption due to fiber and anti-nutrients.	Generally higher digestibility and better absorption rate.
Presence of Anti-Nutrients	Contains anti-nutrients like phytates and lectins, which can hinder mineral absorption.	Absent of anti-nutrients.
Key Nutrients	Often lower in vitamin B12, heme iron, and zinc.	Naturally rich in vitamin B12, heme iron, and zinc.
Processing	Some popular products, like meat alternatives, can be highly processed and contain high sodium.	Typically less processed for comparable forms (e.g., chicken breast vs. vegan patty).

Other Considerations and Challenges

Beyond the primary nutritional concerns, other practical drawbacks of relying on plant-based protein include:

Taste and Texture: Some individuals may find the flavor or texture of certain plant protein sources less appealing than animal products. Processed plant-based alternatives attempt to mimic these qualities, but results vary.
Cost: While basic plant proteins like lentils are inexpensive, some specialized plant protein powders and meat analogues can be more costly than their animal-based counterparts.
Culinary Inconvenience: Ensuring a complete protein intake on a plant-based diet requires more meal planning and variety throughout the day compared to simply eating a piece of meat.
Digestive Issues: The high fiber content in many plant protein sources, while often beneficial, can cause bloating and digestive discomfort in some individuals, particularly during a dietary transition.

Conclusion

While plant-based proteins offer many environmental and health benefits, it is crucial to acknowledge and manage their drawbacks. The primary cons center around the lower bioavailability, incomplete amino acid profiles, and the presence of anti-nutrients, which necessitate a well-planned and diverse diet. Potential deficiencies in key nutrients like Vitamin B12, iron, and zinc must also be addressed through careful planning, fortification, or supplementation. By combining various plant-based foods, using proper preparation techniques, and being mindful of nutritional needs, it is certainly possible to maintain a healthy and balanced diet without relying on animal protein. For those considering a full transition, consulting with a nutrition professional is recommended to ensure all requirements are met. It's a journey that requires awareness and strategy, but the potential benefits for both personal health and the planet can be substantial.

For more information on balancing a plant-based diet, see the American Heart Association's statements on dietary protein needs.

Frequently Asked Questions

Most plant-based proteins are 'incomplete' because they contain lower amounts of one or more of the nine essential amino acids that our bodies cannot produce themselves. Animal proteins, however, typically contain all nine essential amino acids in sufficient quantities.

No, it is not necessary to combine complementary plant proteins in the same meal. The body maintains a pool of amino acids, so as long as you consume a variety of protein sources throughout the day, your body can get all the essential amino acids it needs.

Anti-nutrients are compounds found naturally in plant foods that can interfere with nutrient absorption. Examples include phytates, which can block the absorption of minerals like iron and zinc, and lectins, which can cause digestive issues.

Yes, common deficiencies can include vitamin B12, which is primarily found in animal products, as well as minerals like iron and zinc, which are less bioavailable in plant sources.

On average, the body absorbs plant-based protein slightly less efficiently than animal protein. This is due in part to the fiber content and anti-nutrients found in plants, which can slow digestion.

Yes, it is possible to build muscle effectively on a plant-based diet. Research suggests that with a sufficient and varied intake of plant protein sources, muscle growth is comparable to that of animal protein consumers, especially with resistance training.

Some plant-based protein powders can be high in carbohydrates, may have a grittier texture, and can be more expensive than whey protein. Heavily processed powders may also contain high levels of sodium.

You can improve the digestibility and bioavailability of plant proteins by using proper food preparation methods like soaking, sprouting, and fermenting grains and legumes. Cooking also helps to reduce the impact of anti-nutrients.