One question many fruitarians, raw-fooders and even vegans hear over and over again:

Where do you get your Protein?

This is amazing how many times I heard that! OK, to clarify this, let's split it into three questions:

1. How much protein one needs? ↓
2. How much protein is in plant foods, especially in fruit? ↓
3. Is that the right protein? ↓

How much protein do you need?

Let's start from the very beginning. Children require extra protein for growth. Mother’s milk, the essential food for babies during their fastest growth period, averages just 7% of its calories from protein. This allows an infant to grow by 4.25 kg (9.4 pounds) in 6 months, doubling the body weight. Adults do not need to grow that much, they need to rebuild and repair their bodies, which takes much less essential parts of proteins.

There is 1.1 g/100 ml total protein in breast milk. It is nearly the same is in fruit.

The research tells us that exclusively breastfed babies take in an average of 25 oz (750 mL) per day between the ages of 1 month and 6 months. Different babies take in different amounts of milk; a typical range of milk intakes is 19-30 oz per day (570-900 mL per day).

Thus, a baby consumes on average 8.25 g of protein a day for the first half year of life - ~ 1.5 kg of protein total in this period (182.5days), adding few kilograms (4.25) of high quality body tissues (not just fat).

 Does this make you think?

The science of nutrition is still in its infancy too :) The debate on how much proteins your body needs for optimum health is still going on.

The difficulty of establishing human protein needs arises from the great complexity of food digestion and utilization. The principal method used in studies and experiments is based on the measurement of intake and excretion of nitrogen (specific component of proteins, making 16% of its weight). The assumption is that a balance between nitrogen input and output - adjusted for known interfering factors - indicates the level of protein intake needed to maintain protein level required for body functions. Thus the amount of protein needed for achieving protein balance would equal the minimum safe protein intake for adults (children require extra protein for growth).
However, limitations and incompleteness of (many) conducted tests, coupled with hard to assess changes in protein metabolism due to a number of known and unknown variables has prevented, thus far, arriving to a unanimous result and agreement on this subject.

Officially recommended protein intake can vary significantly from one country to another, much more so than experimentally established protein needs of different human races, or similar races in different world regions.

For an average moderately active adult female, requiring 2400 calories a day, minimum safe protein intake comes to 9% of total calories. And for the average moderately active male requiring 2800 calories a day, minimum safe protein intake makes 8% of the caloric total. A little extra won't hurt, so we can round it off to about 10% of the total calories.

The recommended minimum of daily protein intake is is 0.75g per 1 kilogram of body weight for a lean person. For me it would be approximately 36 g a day. Fruitarian food give up to 250 g protein per 1 kg. Even with only 7 g per 1 kg in some watery fruit, one can eat 5 kg of this fruit and get the estimated amount. 

How much protein needed in a person's daily diet is determined in large part by overall energy intake, as well as by the body's need for nitrogen and essential amino acids. Physical activity and exertion as well as enhanced muscular mass increase the need for protein. Requirements are also greater during childhood for growth and development, during pregnancy or when breast-feeding in order to nourish a baby, or when the body needs to recover from malnutrition or trauma or after an operation.

Risks

A high intake of the amino acid profile that is characteristic of animal-based foods has been associated with the risk of several chronic diseases, including cancer and osteoporosis.

As consumption grows over 5% protein from calories, so do the risks of disease, especially osteoporosis, cancer and kidney problems.

Studies have shown increased calcium excretion in higher animal food diets, which makes bones brittle. Plant based diets have show to increase bone strength.

Hundreds of thousands of studies have linked high protein animal food diets to most every cancer known to man.

Long term consumption of high protein food has shown risks of complete loss of kidney function. The longer term and more consumption of animal foods shows decline in normal kidney function. Risk for kidney stones increases. Researchers in England found that when people added only about 5 ounces of fish (that’s about 34 grams of protein) to a normal diet, the risk of urinary tract stones increased by as much as 250 %.

The average adult protein intake in the US being around 15% of the caloric total (Centers for Disease Control, 1999-2000). It means, that many Americans are at risk.

How much protein is in plant foods?

Lets take a case where a person eats at least primarily juicy fruit: at least 95% of total calorie intake, like I do.

It the table below you see common fruit and percentage of calories from protein in them (counted on 100g):

You can observe that only in few fruit the number is lower than 5% - probably the ideal. One can eat as many fruit as one cares for and get 5-11% of protein of total caloric intake all the time.

Here are some more dense fruitarian foods (fruits, nuts and seeds - one does not need to destroy the plant to obtain them). Just few examples to save time and place:

I genuinely wonder why this information is not evaluable all over the internet - I needed to do the counting myself! Despite the fact that this method of counting is used in most works of nutritionist, there are no databases I could find easily with these numbers.

Is that the right protein?

We do not use complete proteins, we need only their parts to build our own unique proteins, thousands of them. Amino acids are the building blocks of protein, there are 22 of them total and 14 we can surely synthesize ourselves, they are not essential.

Proteins are harder for the body to use for energy, they normally satisfy less than 10% of its caloric needs. Your organism will burn proteins only when its preferred energy sources are not available (carbohydrates and fats).

These amino acids can abundantly be found in plant based foods, where the animals get them. The amino acid profile of staple foods is rarely if ever a limiting factor in human nutrition. The only common food that represents an "incomplete" protein is gelatin.

Proteins from plant sources contain adequate amounts of all of the amino acids that are essential in human nutrition. Dr. John A. McDougall, M.D.:

"All the essential and nonessential amino acids are represented in single unrefined starches such as rice, corn, wheat, and potatoes in amounts in excess of every individual's needs, even if they are endurance athletes or weight lifters."

Our body gets all but 1/6 of the protein it needs from recycling old body tissue. This 1/6 must come from essential amino acids we eat.

Amino acids

Eight amino acids are generally regarded as essential for humans: phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, and lysine. The distinction between essential and non-essential amino acids is somewhat unclear, as some amino acids can be produced from others. 

The following table lists the World Health Organization (WHO) recommended daily amounts currently in use for essential amino acids in adult humans and amounts in common juicy fruit (my weight is normally a little under 50 kg):

Theoretically, a person can cover the daily need with .5 kg (1 pound) of fresh green peas or with 160 g of peanuts only. However, different proteins have different levels of biological availability to the human body. Many methods have been introduced to measure protein utilization and retention rates in humans, but none of them are fully reliable.

Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it. A PDCAAS value of 1 is the highest, and 0 the lowest. Ratings of some groups of food: casein (milk protein) - 1, soy protein - 1, soybeans - 0.91, chickpeas - 078, fruits - 0.76, vegetables - 0.73, legumes - 0.7, cereals - 0.59.

The PDCAAS measures the quality of a protein based on the amino acid requirements (adjusted for digestibility) of a 2- to 5-year-old child (considered the most nutritionally-demanding age group). The PDCAAS takes no account of where the proteins have been digested. 

Combination

Eating various plant foods in combination can provide a protein of higher biological value. However, vegetarians do not need to intentionally combine different foods for this purpose. 

Grain protein has a PDCAAS of about 0.4 to 0.5, limited by lysine. On the other hand, it contains more than enough methionine. White bean protein (and that of many other pulses) has a PDCAAS of 0.6 to 0.7, limited by methionine, and contains more than enough lysine. When both are eaten in roughly equal quantities in a diet, the PDCAAS of the combined constituent is 1.0, because each constituent's protein is complemented by the other.

By eating a variety of fruits we can naturally get the perfect score protein. I don't think we need it though.

Enzymes

For some reason enzymes - long, linear chains of amino acids - seem not to be considered by protein counting in foods (?). All fresh plant foods are full of them. Here is what an athlete Tim Van Orden says about amino acids from enzymes:

To be continued...

Excellent breakdown Lena, thanks for posting it.