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The discussion of protein boils down to one simple question…

Where should we get our protein – from plant or animal sources?

The purpose of this article is to answer this query and examine the health risks associated with the overconsumption of protein.

Why More Is Not Necessarily Better

While we can all agree that protein is an essential building block for our muscles and cells, the exact amount of protein we need is the subject of hot debate.

One thing for sure is that historically we have struggled to get the number right.

But over time, we have realized that less is better.

This protein ‘craze’ began over 100 years ago and reached its peak in the 1950s when the United Nations declared protein deficiency a serious threat to health worldwide. Around that time, high protein diets started to emerge, and average weight people were encouraged to eat as much as 100 grams per day.

As it turns out, however, there was little evidence of a dietary protein deficiency, and by the 1970s a massive recalculation of human protein requirements was undertaken. Today, as we talked about in our article Protein—Too Much of a Good Thing? the recommended amount is ~54 grams per day (for a 150 lb. person), half of the level suggested in the 50s.

Furthermore, we have discovered that too much protein (versus too little) can pose a serious health risk. The adverse effects associated with long-term high (animal) protein diets include bone and calcium imbalance, kidney dysfunction, liver problems, increased cancer risk, and worsening of coronary artery disease.

What Is a Protein Exactly?

To understand the controversy, which swirls around proteins, we first need to know how proteins are formed.

Proteins are made up of amino acids. Amino acids are the building blocks of life, promoting growth and regulating almost every biochemical reaction in the body.

The human body uses 20 amino acids in various combinations to form proteins. While the body can make 11 of them, the other nine—or the so-called essential amino acids—must come from our diet.

The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

All plant foods provide the nine essential amino acids, but their relative concentrations vary in comparison to animal foods.  And this distinction makes all the difference! (which we will discuss in a bit.)

How Can You Calculate Your Protein Needs?

There are a few ways to calculate how much protein you need.  We covered two methods in detail in our article Protein—Too Much of a Good Thing?

Adults need no more than 0.8 grams of protein per kilogram of  healthy body weight per day.

If you keep track of your weight in pounds, the ‘classical’ method is a simple two-step process, where you divide your current weight by 2.2 to get your weight in kilograms then multiply that number by 0.8.

An alternative way is to multiply your weight in pounds by four, then divide it by ten. The result is the total grams of protein you require each day.

In practical terms, a 120 lb. person needs 44–48 grams of protein per day. And that amount can be easily obtained when you consume enough calories to maintain a healthy weight and eat an unprocessed or minimally processed, plant-based diet that is also low in (or devoid of) added fats and oils.

The Connection Between Protein and Cancer: Understanding IGF-1

What is the connection between animal protein and cancer, if anything?

To understand the link, we must first understand IGF-1.

As suggested by its name, IGF-1 (or insulin-like growth factor 1) is a hormone similar in molecular structure to insulin. Instrumental to normal growth during our childhood, IGF-1 in adulthood can promote continuous proliferation of cells, which may lead to the onset and progression of cancer and other chronic diseases.

If our levels of IGF-1 stay too high when we are adults, it is a constant message to our cells that they should multiply. This means that the higher the IGF-1 levels in our bloodstream, the greater our risk for cancer.

So the question is what triggers elevated IGF-1?

Is it the amount of protein we eat or the type of protein?

Research gives us the answer.

A study of meat-eaters, vegetarians and vegans revealed no variance in IGF-1 levels between those who consumed a lot of protein and those who ate a little (i.e. when they looked at the amount of protein alone).   However, when they compared the source of the protein (i.e. whether it was animal- or plant-based), they observed a clear difference.

When protein was animal-based, a higher IGF-1 level was detected, which might encourage cancerous cell growth. On the other hand, when plant protein was consumed, the exact opposite happened—levels of IGF-1 decreased, thus discouraging the development of cancer cells.

Thus, cancer risk may vary whether the protein is animal- or plant-based.

Another study supported this theory , showing that combining walking and a plant-based diet for as little as 11 days may decrease IGF-1 levels and lead to slow (or even reversed) cancer growth.

Moreover, the research revealed that those who followed a vegan diet experienced much better results than vegetarians. This suggests that the more plant-based your diet is, the lower your risk of hormone-dependent cancers may be.

Further, a person who eats a plant-based diet over a full year may suppress cancer cell growth nearly 8 times more than someone who follows the Standard American Diet.

The reduced cancer risk, which comes from eating plant-based protein, may be, in part, related to two factors.

  • On the one hand, IGF-1 levels drop significantly.
  • But also, IGF-1 binding protein levels rise.

We understand why lower IGF-1 levels can help prevent cancer.

But why is an increased level of IGF-1  binding protein important?

One of the ways our body protects itself from excessive cellular growth is by releasing a binding protein that can ‘attach’ to ‘free’ IGF-1 in our bloodstream. This binding protein acts as the body’s ‘emergency brake,’ slowing the cellular growth process.

People who eat plant-based diets over the long-term (i.e. over 14 years) have half the IGF-1 levels in their bodies and more than twice the amount of IGF-1 binding protein than those who consume a Western diet.

But what if going 100 percent plant-based is too dramatic for you? What happens if instead you simply shift the ratio of animal to vegetable proteins from 2:1 (animal:plant) to a more even 1:1 split?

A study on prostate cancer patients did just that. And while altering the ratios did not stop the cancer growth, it did seem to slow its doubling time down considerably, from 21 months to 58 months.

And the largest study ever performed on the relationship between nutrition and bladder cancer showed that even a mere 2 percent increase in plant protein consumption could cut your cancer risk a whopping 23 percent (while a 3 percent increase in animal protein consumption could raise bladder cancer risk by 15 percent.).

In other words, even little changes in our diet have significant effects.

And There Are More Risks to Your Health

Eating animal protein has recently been linked to an early onset of puberty.

More specifically, every gram of daily animal protein intake is associated with a 17 percent increase in girls starting their periods before the age of 12. Plant protein consumption appears to have the opposite effect, delaying the onset of puberty on average by seven months.

Early puberty is commonly known as a risk factor for a wide variety of adulthood diseases including hormone-related cancers, metabolic syndrome, and cardiovascular disease.

At the same time, the consumption of animal-based protein can also shorten your life altogether.

Rosane Oliveira, DVM, PhD

President & CEO, Plant-Based Life Foundation | Dr. Rosane Oliveira combines a lifelong passion for nutrition with 25 years of genetics research to create programs that help people develop healthy habits on their journey towards a more plant-based lifestyle. She is a Visiting Clinical Professor in Public Health Sciences and was the founding director of the first Integrative Medicine program at the UC Davis School of Medicine. She completed her postgraduate studies in Brazil and did her postdoctoral training in immunogenetics and functional genomics at the University of Illinois at Urbana-Champaign.