You need protein to build, maintain and repair every cell in your body — from bones and muscles to skin and hair. All foods contain some protein. Protein from soy and animal-based protein each have different merits and advantages for your health. If you consider not only the nutritional benefits, but how each type can influence your risk for certain chronic disease, you can make an informed decision on your choice of protein.
What Is Soy?
Soy comes from soybean plants, which belong to the legume family. The beans can vary in color from green, black, white or yellow. Soybeans are a high-protein versatile food available in many forms (whole soybeans, edamame, tofu, tempeh, soy milk and soy chips) and eaten in many ways, including raw, boiled, sprouted, fried and roasted. Soybean extracts, such as soy-protein isolate, soy-protein concentrate or soy-protein flours are used to make dairy alternatives and infant formulas.
What Is Protein?
The food you eat contains a variety of nitrogen-containing organic compounds, called amino acids. Your body combines 20 of these amino acids in specific amounts and bonds them together to create long chains called proteins. These proteins form the structural and functional components of all your cells.
Your body has the ability to make 11 amino acids. These are known as nonessential. The remaining nine are known as essential amino acids because your body needs to acquire them from the food you eat. Each essential amino acid plays a different role in helping your body function and is required in different amounts. Many foods contain one or more of each type of amino acid.
What Is a Complete Protein?
Most plant foods lack some of the essential amino acids, so you should eat a variety of fruits, nuts and vegetables to be assured that your diet has all the building blocks it needs to make adequate protein. Some foods contain all nine of the essential amino acids — they're considered complete proteins.
Animal products, such as meat, chicken and poultry, are complete proteins. The right plant-based foods can also be excellent sources of protein, often with fewer calories than animal sources. In addition to soy and soy products, other plant-based foods considered complete or exceptional in protein content are:
- Chia seeds
- Pumpkin seeds
- Sprouted brown rice
- Ezekiel bread
How Much Do I Need?
Dietary Guidelines for Americans recommends that your intake of protein consist of 10 to 35 percent of your daily calories. That equates to about 50 to 175 grams of protein a day on a 2,000-calorie diet. The recommended dietary allowance for protein is 46 grams a day for women and 56 grams for men. The Harvard T.H. Chan School of Public Health warns that protein deficiency can result in growth failure, weakening of the immune system, loss of muscle mass, reduced functioning of the heart and respiratory system, and even death.
Meat protein comes in many forms, all of which assure you're getting all the amino acids in each complete-protein food. For comparison, some examples of the content of protein in meat, per 3-ounce serving, are:
Although many plant proteins don't contain all the essential amino acids, soy products are one of the richest sources of protein in the plant kingdom. Soy contains all the nine essential amino acids and is considered a complete protein. However, it has a relatively low level of tryptophan, so you need to eat other protein sources along with soy to ensure adequacy.
Each form of soy differs slightly in protein content depending on how it's prepared. The following amounts are per 3/4 cup serving, or 150 grams:
So the protein content of several soybean products is comparable to that of meat-based protein. A serving of mature soybeans has more protein than a serving of beef steak. The amount of protein in tofu is also significantly higher per serving than that of chicken breast.
Nutritional Advantages of Meat Protein
Meat protein benefits include supplying some nutrients that may be lacking in soy and plant food. Some minerals are also better absorbed from animal protein compared to soy.
Your body needs vitamin B12 to keep nerve and blood cells healthy. In addition, it's needed for the production of DNA, the genetic material in your cells. The National Institutes of Health (NIH) recommends a daily average intake of 2.4 micrograms a day of vitamin B12 for adults and more for pregnant and breastfeeding women. A vitamin B12 deficiency can cause fatigue, weight loss, nerve problems, depression and poor memory.
Vitamin B12 is readily available in meat and meat-based products. However, it's lacking in soy protein and other plant foods. Many people who rely on soy protein are likely to be deficient in B12. A report from a study published in the European Journal of Clinical Nutrition in 2014 found that up to 86.5 percent of adults had a deficiency, with higher deficiency prevalent in vegans and vegetarians.
Vitamin D is a fat-soluble vitamin found in some animal-based proteins. It's necessary for calcium absorption and needed for proper bone formation and maintenance. Without vitamin D, your bones would become brittle and your immune system possibly compromised. You can get it from sunshine, but soy products do not contain vitamin D.
Iron is vital to the production of hemoglobin in your body. Two forms of iron have been identified: heme and nonheme. Plants contain nonheme iron only, while meat protein, predominantly red meat, contains both heme and nonheme iron. Compared to the iron in soy, the heme iron in meat is the most easily absorbed type, according to NIH. The recommended intake for iron is between 8 and 18 milligrams, depending on age and gender.
Zinc plays a role in many aspects of cellular metabolism in your body, including protein synthesis, wound healing and cell division. It's recommended that you get 11 milligrams for adult males and 8 milligrams for females daily. Zinc is found primarily in animal protein sources. Although soy contains some zinc, it isn't as easily absorbed and used by your body as that from meat protein, according to University Health News.
Nutritional Advantages of Soy Protein
Although a carnivorous diet can be healthy, it may lack many important nutrients that are specific to plant protein. Getting your protein from soy foods can provide some vitamins and micronutrients that meat doesn't offer.
Important as an antioxidant for your immune system, vitamin C is also involved in protein metabolism and is necessary for the absorption of nonheme iron that’s present in plant-based foods. Vitamin C is abundant in many plant foods, including soy, but is not found in useful amounts in animal foods. The USDA recommends a daily intake of 75 milligrams for adult women and 90 milligrams for men. Not getting enough vitamin C in your diet may lead to iron-deficiency anemia.
Flavonoids are a diverse group of phytonutrients found only in plants. Soybean and soy products, including tofu, tempeh, miso and edamame, are the richest and most concentrated source of these powerful antioxidants available, says the Linus Pauling Institute. Of those, edamame, or green soybeans, contains the highest amount — 138 milligrams per 3/4 cup — followed by cooked soybeans, with 81 milligrams for the same amount.
Dietary flavonoids have been studied extensively for their role in promoting health and preventing disease. A study published in the journal Medicines in 2017 reported that an intake of dietary soy during the early stages of life may provide protection against breast cancer in adulthood.
The anti-inflammatory benefits and immune system benefits from flavonoids in plants may be a contributing factor to the association of reduced risk of cardiovascular disease, as discovered in a study published in the British Journal of Nutrition in 2014.
In addition, the antioxidants in soy isoflavones have been associated with a possible reduced risk of certain cancers, including prostate cancer.
Dietary fiber is defined as the parts of food that can't be digested and form roughage, or bulk, that contributes to the health of your digestive system. Fiber can help prevent constipation and diarrhea.
Dietary Guidelines recommends a daily intake of 28 to 33.6 grams for men and 22.4 to 28 grams for women, depending on age. Plant food, including soy, contains an abundance of fiber, but meat doesn't provide any significant amount.
Fiber contributes to a feeling of fullness after a meal, which may help you eat less. A high intake of fiber was linked to weight management in a 2017 study published in the Journal of Nutrition and Metabolism.
Comparison of Effect on Cholesterol
Because cholesterol is needed to build healthy cells in the body, the USDA has not set an upper limit for cholesterol intake. However, the American Heart Association (AHA) warns that too much can cause health problems for some people. Excessive LDL, the “bad” cholesterol, can build up on the inner walls of your arteries and reduce the amount of blood and oxygen your heart and brain receive.
The AHA advises that replacing foods high in animal fat with foods containing soy protein may be beneficial to the health of your heart. Evidence suggests that soy may even contribute to lowering cholesterol.
A 2015 report from Health Canada Food Directorate encompassed 79 previous studies in a meta-analysis to compare the protein content of soybean to animal protein sources. The aim of the study was to assess total cholesterol, LDL, HDL and triglyceride levels.
Researchers found a reduction of total cholesterol and LDL in a high percentage of the studies involving the group that consumed soy protein. Findings also showed a significant increase in HDL and reduction in triglyceride levels in the overall analysis. Health Canada concluded that their scientific evidence supported the claim that soy protein is shown to reduce or lower cholesterol.
Estrogen in Soy:
If you choose to get the majority of your protein from soy foods, you may have some concern about the possibility of isoflavones in soy causing a disruption of the estrogen-sensitive systems in your body, including your reproductive system.
However, a 2016 study, published in Nutrients, reports that it supports the conclusion of the European Food Safety Authority that says isoflavones have no adverse effects on the breast, thyroid or uterus of postmenopausal women.
Allergies or food sensitivities may be of concern when consuming protein. Soy allergies are very common and often start in infancy with soy-based infant formula causing a reaction. Although it's possible to outgrow soy allergy, you may carry it into adulthood.
Some of the symptoms and signs of soy allergy, that may develop within a few minutes to hours after eating soy include:
- Tingling in the mouth
- Hives with itchy, scaly skin
- Swelling of the lips, face, tongue and throat
- Wheezing or breathing difficulty
- Stomach pain, diarrhea, nausea or vomiting
- Flushing of the skin
The American College of Allergy, Asthma and Immunology warns that eating meat from any kind of mammal — beef, lamb, pork or goat — can cause an allergic reaction in some people. The Lone Star tick, found mostly in the Southeast from Texas to Iowa and into New England, has been implicated in causing the red meat allergy. If you're allergic to a certain type of meat, it's possible you could also be allergic to other meats as well.
Some symptoms of a meat allergy include:
- Hives or skin rash
- Nausea, stomach cramps, indigestion, vomiting, diarrhea
- Stuffy or runny nose
- Dietary Guidelines 2015-2020: Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations
- USDA: Food Composition Databases
- Vegan Protein Lab: Soy Protein Amino Acid Profile
- NIH Office of Dietary Supplements: Vitamin B12
- European Journal of Clinical Nutrition: The Prevalence of Cobalamin Deficiency Among Vegetarians Assessed by Serum Vitamin B12
- NIH Office of Dietary Supplements: Vitamin D
- NIH Office of Dietary Supplements: Iron
- University Health News: Plant Protein vs. Animal Protein: Which Is Best for Your Health?
- NIH Office of Dietary Supplements: Vitamin C
- Linus Pauling Institute: Soy Isoflavones
- Dietitians of Canada: What Are the Health Benefits of Soy?
- Medicines: Dietary Isoflavones and Breast Cancer Risk
- British Journal of Nutrition: Flavonoid Intake and Risk of CVD
- The Journal of Steroid Biochemistry and Molecular Biology: Soy Isoflavones and Prostate Cancer
- Journal of Nutrition and Metabolism: Dietary Fiber Intake Among Normal-Weight and Overweight Female Health Care Workers
- BMJ: Dietary Fibre Intake and Risk of Cardiovascular Disease
- Nutrients: Soy and Health Update
- Harvard T.H. Chan School of Public Health: Protein
- Medical News Today: Top 15 Sources of Plant-Based Protein
- MedlinePlus: Amino Acids
- American Heart Association: Control Your Cholesterol
- Health Canada Food Directorate: Summary of Health Canada's Assessment of a Health Claim About Soy Protein and Cholesterol Lowering
- Mayo Clinic: Soy Allergy
- American College of Allergy, Asthma and Immunology: Meat Allergy
- UC Davis Integrative Medicine: The Essentials–Part One