About 20% of the human body is made up of protein.
Because your body doesn't store protein, it's important to get enough from your diet each day.
You can get protein from many food sources, including plants and animals.
Some people claim that the source of the protein, whether animal or plant, shouldn't matter.
Others suggest that plant protein is superior to animal protein.
This article compares animal and plant proteins.
When eaten, protein is broken down into amino acids.
Proteins and amino acids are used for almost every metabolic process in the body.
However, different proteins can vary greatly in the types of amino acids they contain.
While animal proteins tend to contain a good balance of all the amino acids that we need, some plant proteins are low in certain amino acids.
For example, some key plant proteins are often low in methionine, tryptophan, lycine and isoleucine.
Bottom Line: All proteins are made up of amino acids, although the amount and type of each amino acid varies based on the protein source.
In total, there are around 20 amino acids that the human body uses to build proteins.
These amino acids are classified as either essential or non-essential.
Your body can produce non-essential amino acids. However, it cannot produce essential amino acids, which need to be obtained through your diet.
For optimal health, your body needs all the essential amino acids in the right ratios.
These are considered to be complete sources of protein because they contain all of the essential amino acids that your body needs to function effectively.
Some sources report soy protein as complete. However, two essential amino acids are only found in small amounts in soy, so it isn't comparable to animal protein (2).
Bottom Line: Animal foods are the highest quality protein sources. Plant sources lack one or more amino acids, which makes it more difficult to get all the amino acids that your body needs.
Of course, proteins are rarely found in isolation. They usually come with a wide variety of other nutrients.
Foods that contain animal protein tend to be high in several nutrients that are often lacking in plant foods.
- Vitamin B12: Vitamin B12 is mainly found in fish, meat, poultry and dairy products. Many people who avoid animal foods are deficient (3).
- Vitamin D: Vitamin D is found in oily fish, eggs and dairy. Some plants contain it, but the type found in animal foods is better used by your body (4).
- DHA: Docosahexaenoic acid (DHA) is an essential omega-3 fat found in fatty fish. It's important for brain health and is hard to get from plant sources (5).
- Heme-iron: Heme-iron is predominantly found in meat, especially red meat. It is much better absorbed in the body than non-heme iron from plant foods.
- Zinc: Zinc is mainly found in animal protein sources, such as beef, pork and lamb. It is also more easily absorbed and used from animal protein sources (6).
Of course, there are also plenty of nutrients found in plants that are lacking in animal foods. Therefore, eating balanced amounts of both is the best way to get all the nutrients you need.
Bottom Line: Animal protein sources are higher in certain nutrients, such as vitamin B12, vitamin D, the omega-3 fatty acid DHA, heme-iron and zinc.
Red meat is a high-quality protein source.
However, further research has suggested that the problem is not with all red meat, but rather with processed red meat.
In a large observational study including 448,568 individuals, processed meat was linked to an increased risk of death, with no effect for unprocessed red meat (10).
Another study involving over 34,000 women made similar observations. In this case, processed meat was associated with heart failure (11).
Also, a large review of 20 studies found that processed meat was associated with an increased risk of heart disease and diabetes. Again, no association was found for unprocessed red meat (12).
Despite this, one study found that replacing 1 serving per day of red meat with 1 serving of poultry was associated with a 27% lower risk of stroke (7).
Furthermore, the health risks associated with processed red meat are not linked to fish and other meats, such as turkey and chicken.
Bottom Line: Processed red meat is associated with an increased risk of disease. Unprocessed red meat and other lean meats are generally healthy.
Diets high in plant protein, such as the vegetarian diet, are linked with many health benefits.
Studies suggest vegetarians tend to have a lower body weight, lower cholesterol and lower blood pressure levels.
They also have a lower risk of stroke, cancer and death from heart disease than non-vegetarians (15).
Lower Risk of Heart Disease
A study found that a diet rich in protein (about half from plants) lowered blood pressure, cholesterol levels and the risk of heart disease more than a standard diet or a healthy high-carb diet (16).
Reduced Risk of Type 2 Diabetes
However, another small 6-week study of diabetics compared a diet high in plant protein with a diet high in animal protein. No differences were found in blood sugar, cholesterol and blood pressure (19).
Protection Against Weight Gain
Diets high in plant protein may also help you control your weight.
Also, eating one serving of beans, chickpeas, lentils or peas per day can increase fullness and may lead to better weight management and weight loss (21).
Correlation Does Not Imply Causation
It's important to remember that observational studies only report statistical associations. They cannot prove that these benefits were caused by eliminating meat or other animal protein sources.
One thing to consider is that people on vegetarian diets tend to be more health-conscious than the general population (22).
Bottom Line: A diet high in plant protein is linked to a lower risk of heart disease, diabetes and obesity. This may be explained by an overall healthier lifestyle in vegetarians.
Animal protein is also associated with positive health effects, despite often being portrayed as unhealthy compared to plant protein (26).
The Nurses' Health study reported that poultry, fish and low-fat dairy were associated with a lower risk of heart disease (27).
People who eat fish regularly are also likely to have a lower risk of heart attacks, strokes and death from heart disease (28).
One study of more than 40,000 males found that those who regularly ate one or more servings of fish per week had a 15% lower risk of heart disease (29).
Additionally, eating eggs has been linked to improved cholesterol levels and weight loss. In one study, women who ate eggs for breakfast, rather than a bagel, reported feeling fuller and ate less later in the day (30, 31, 32).
Bottom Line: Certain animal protein sources are linked to a reduced risk of heart disease, improved cholesterol levels, weight loss and increased muscle mass.
For optimal health, the evidence supports a diet that is low in processed meat, rich in plant protein, with some animal sources such as grass-fed meat, fish, poultry, eggs and dairy (37).
As plant protein food sources often have lower quality proteins, vegetarians and vegans should eat a wide variety of foods to ensure that they are getting all the amino acids that they need.
For meat eaters, it's important to get the right balance of both animal and plant foods.