September 12, 2023 | 8 minute read

Protein is a hot topic, and today’s headlines about the importance of protein may leave you wondering, “can I get enough protein if I limit red meat on my cancer-prevention diet?” The answer is yes!

About two-thirds of the protein in the average American diet comes from animal foods, and meat is the single largest source. But just because many people eat that way now, doesn’t mean that it’s the only way to get enough protein. Read on to understand how much protein you need and how plant-based protein plays a role.

Why Do I Need Protein?

Protein is essential for everyone. Your body uses it to create enzymes that are vital for hormones, immune system cells and antibodies. Protein is required for growth and to build and maintain muscle and other body tissues.

Protein is made from building blocks called amino acids. As the protein you eat is digested in the body, it’s broken down into individual amino acids or peptides (short chains of amino acids). These are then recombined to make functional proteins, structures and new cells needed by your body.

How Much Protein Do I Need?

The Recommended Dietary Allowance (RDA) for protein varies by age. For adults, the RDA is 0.8 grams/kg of body weight (about 0.36 grams of protein per pound of body weight). That means that for an adult who weighs 130 pounds, the RDA is 47 grams (1.7 oz) of protein per day, and for someone who weighs 170 pounds, the RDA is 62 grams (2.2 oz) of protein per day.

Growing research suggests that protein beyond the RDA may benefit some people:

• People ages 70 and older may require more protein to maintain muscle and bone health. Current evidence suggests that 1.0 to 1.2 grams of protein/kg body weight (about 0.45 to 0.55 grams of protein per pound of body weight) may be best for adults 70+, but research is still underway.
• Some medical conditions and treatments may call for protein beyond the RDA. This includes people receiving or recovering following cancer treatment. Assessment by a registered dietitian nutritionist identifies how much protein needs increase, depending on factors like someone’s age, type of cancer and its treatment and whether malnutrition is already present.
• Athletes may benefit from protein beyond the RDA. The optimal amount varies, since endurance athletes do not need as much additional protein as those involved in a lot of high-intensity muscle-building. Research suggests a range from 1.2 to 2.0 grams/kg body weight for most athletes.

Is More Protein Better?

More is not always better, and you can’t direct how protein is used. If you eat more protein than you need, it doesn’t force your body into super-building mode to create extra immune cells or more muscle.

Eating more protein will not build muscle without appropriate exercise. Studies show that resistance (strength-building) exercise drives building more muscle. Having enough protein provides the raw materials, but it is not enough on its own.

Excess protein gets treated as extra calories. When the body’s pool of amino acids from protein is more than needed, extra amounts can be converted to glucose (sugar) or used to meet calorie needs.

Your whole diet matters. For protein to be used for building muscle, immune cells or anything else, your diet needs to provide enough calories and the other nutrients needed in the “building” process. For example, people with side effects of cancer treatment are at risk of sarcopenia (loss of muscle or strength). And simply increasing protein isn’t enough if they don’t consume the calories they need.

What Is Complete Protein?

A food is considered a source of complete protein if it contains all nine essential amino acids. Your body uses protein as a source of amino acids to build new body proteins. Some amino acids can be produced within the body. Nine amino acids, however, are called “essential” because the body can’t make them, and they need to come from protein in your diet.

Complete proteins are mostly animal-based foods, such as fish, poultry, eggs and dairy. But, some plant foods are also complete proteins, including:

• Soy foods such as tofu and edamame
• Hemp and chia seeds
• Buckwheat
• Quinoa
• Nutritional yeast

Can I Get All the Essential Amino Acids from Plant Foods?

Yes! In addition to the complete plant-based protein foods listed above, you can create complete proteins by eating a variety of grains, legumes, nuts, seeds and vegetables.

Since a healthy plant-based diet includes a wide variety of meal choices, foods that are slightly low in one amino acid can be balanced by other foods that are higher in that amino acid. For example, grains are slightly low in the amino acid lysine, but dry beans and lentils are high in lysine. If you eat a variety of plant foods, there’s no need to worry about getting all the required amino acids that you need.

Past research suggested that amino acid absorption from protein in plant foods might be slightly lower than from animal foods. But these concerns came mainly from animal studies and used uncooked legumes and grains. Current evidence shows that amino acid absorption from a plants-only diet is essentially the same as from a diet with animal foods. Studies also show that even people eating plants-only diets almost always get protein beyond the RDA as long as they are meeting their caloric needs.

Do I Need to Combine Certain Foods to Get Enough Protein?

Your body does the combining for you, so this is not a concern. Studies have long shown that body pools of amino acids are enough and that eating a varied diet day after day is fine. You don’t need to worry about food combining at each meal.

Decades ago, the limited essential amino acid content in some plant foods led to advice to make sure that a plants-only diet included specific combinations of foods (like grains and beans). The idea was that they balanced each other in amino acids provided. Outdated advice about proteins continues to circulate on the Internet and makes a plant-focused diet seem more complicated than it is.

Where Can I Get Protein if I Limit Red Meat?

Many different plant foods can contribute to supplying the protein you need. Grains, pulses (like dry beans and chickpeas), soy foods, nuts and seeds are the major plant sources of protein. But vegetables also provide protein.

Some people may choose to include only plant foods in their diet, but you can also eat a cancer-preventive plant-focused diet and still include moderate portions of poultry, fish, eggs and dairy products.

The AICR Cancer Prevention Recommendations call for limiting red meat like beef, lamb and pork to no more than 12 to 18 ounces per week. Save processed meats like bacon, sausage and cold cuts for occasional use. These steps will reduce your risk of colorectal cancer.

How Much Protein Is in Foods?

A 3-ounce serving of fish or poultry has about 20–25 grams of protein. Plant-based foods also contain protein. Here’s how they add up:

Why Eat More Plant Protein?

Eating more plant foods can provide plenty of protein and improve your overall diet quality without raising food costs. But, meals have to be planned to include a variety of foods. The two main obstacles to meeting protein needs with plant foods are:

• If total calorie consumption is too low.
• If large amounts of low-nutrient foods and drinks crowd out nutrient-rich foods. For example, sugary foods and French fries are foods that technically come from plants (sugar cane and potatoes) but are not rich in nutrients.

You have lots of options for getting the protein you need from the plant-focused diet that’s recommended for cancer prevention. Some people may choose to include modest amounts of red meat several days a week. Others may choose red meat rarely or never, and include other poultry, fish or dairy products frequently. Still others may eat a plants-only diet.

Regardless of your eating style, start with AICR’s New American Plate. It clarifies the key steps to creating a cancer prevention diet. You can choose the specifics of how to put it into practice to fit your nutritional needs and food preferences.