Protein needs

The first thing to appreciate about protein is that it is only one component of food: there are no “protein foods” that are all protein. A second point is that all living cells contain protein: neither animals nor plants have a monopoly on protein. In fact, only the plants are able to synthesize amino acids from scratch.

Where do we get our protein from on a whole foods plant based diet?

The short answer is: from plants, the long answer is as follows:

Since protein was discovered in the nineteenth century it has been considered the nutrient of prime importance, and this is roughly what the word protein means. Recommendations for protein intake have varied between different authorities and through time. The first dietary recommendation for protein intake was simply based on measurements of how much protein German manual workers consumed, 118g per day. Recommendations for protein intake are often based on culture as much as science. Multiple safety factors are added on to the known minimum requirements to establish a recommended intake which even then tends to be interpreted as an absolute minimum which we must remain well above.

We only need about 40g of protein per day. Expressing protein needs in terms of percentage of energy intake is useful because the same approximate number can be recommended to everyone, regardless of size or level of physical activity. For a detailed discussion of macronutrients as a percentage of energy intake see our Energy Pie page. Intakes of 10-20% are recommended in affluent nations.

The minimum requirement for protein is about 5-6% of calories. Safety margins to cover individual variation and issues of protein utilisation increase this to 8-10% of calories. It is no coincidence that a diet consisting of whole plant foods provides at least this amount. And this figure already has safety margins so that if you did manage to design a plant based diet with less than 8-10% protein, which would be difficult, you probably still would not manage to experimentally give yourself protein deficiency.

Protein values for selected foods expressed as a percentage of calories:

  • Potato             6-11%
  • Oats                14%
  • Rice                  8%
  • Bread              16%
  • Lentils              27%
  • Almond           12%
  • Egg                 35%
  • Human milk      4%
  • Olive oil             0%
  • Sugar                0%

It is interesting that human breast milk is so low in protein yet provides adequate protein for our most rapid period of growth.

For those involved in body building and strength training a low protein diet is usually inconceivable. We can work within their paradigm by simply shifting the diet more in the direction of higher protein grains and legumes.

For a long time it was thought that there was widespread protein deficiency in the world and that the answer was to provide poverty stricken regions with more meat and dairy foods. This fallacy arose from the fact that our bodies can also use protein as a fuel, and in starvation states, the body’s own tissues are metabolised for energy. This “protein deficiency” can only be corrected by consuming adequate calories, and it does not matter whether these calories come from animals or whole plant foods. Potato, for example, has adequate protein to rehabilitate starving children.

Protein requirements cannot be considered in isolation from other nutrients. Carbohydrates are said to have a protein sparing effect. When our bodies run low on carbs, our protein reserves are consumed in a one way process to maintain adequate blood glucose levels. Another reason to avoid low carb diets.

We have all heard the term “quality protein”. And some of us remember the protein complementarity charts that were designed to enable vegetarians to obtain quality protein by combining different food such as grains and legumes. Is plant protein inferior? No is the short answer. The long answer is that it all began in 1913 when Mendel and Osborne reported that young rats grew faster on animal versus vegetable sources of protein. This finding resulted in meat, eggs, and dairy foods being classified as superior, or “class A” protein and vegetable proteins classified as inferior, or “class B” proteins. Seems no one considered that rapidly growing rats are different to humans. A striking example of the difference in the nutritional needs of rats compared to humans is that rat breast milk is 11 times more concentrated in protein than human breast milk. So eggs do contain the perfect protein, but only if you are a young rat.

The 1970’s publication, Diet for a Small Planet, had charts on how to combine plant protein foods to ensure adequate high quality protein. The second Jeff Novick link at the bottom of this page includes quotes from the author of this book explaining why she did this and how she no longer considers such protein combining to be necessary.

Now for some biochemistry: All proteins are built from 20 different amino acids. Human cells can interconvert many of these but there are 8 that cannot be interchanged. Take away any one of these 8 and protein cannot be made: it’s like an assembly line with one critical component missing. The theory was that some plant sources, such as grains, were low in one or more of these 8 amino acids, particularly lysine, and were said to be low quality or incomplete proteins. There are several reasons why this is not a problem to plant eating humans.  Firstly, there are no plant foods which are completely lacking in any essential amino acid. Secondly, we don’t need a high intake of every essential amino acid at every meal because our bodies maintain a pool of several days’ worth of amino acids. And thirdly, a whole foods plant based diet provides well in excess of our minimum protein needs.

Provided that you consume adequate calories, obtaining enough protein from a whole foods plant based diet need not be of concern. There are much more serious issues to be considered in connection with protein intake. See Animal protein page (under construction).