Protein From Plants ? Bad Idea (unless you're a plant)
Proteins form the building blocks of our bodies. Plant proteins build plants, we are not plants (at least I'm not, are you ?) Humans should source their protein from animals for the simple reason that WE are animals too.
Why do we eat ? In mainstream discourse we mostly consider food in terms of energy. This in turn reflects a high carbohydrate way of eating where energy levels are largely driven by blood glucose and need topping up every few hours. It also sits well with the 'Calories In - Calories Out' (CICO) model where food intake has to be carefully and consciously matched with energy usage - if we forget or miscount our calories we will inevitably get fat, according to this way of thinking.
Food as energy, however, is only one small part of the picture. Most of us are walking around without least one or two months' supply of fuel in the form of fat stores, so if the function of eating was simply to provide energy then there would be no good reason to do so for all but a few top class athletes, not for quite some time anyway.
The main function of food is not to supply energy, but NUTRITION. Nutrients are the components our bodies are made up of, and they exist to replace and rebuild these are they are used up. This is one reason why carbohydrates have no real place in nutrition - we have minimal amounts of carbohydrate in our body composition, some glycogen stores, maybe a teaspoon of glucose in our blood, and these we make ourselves under tightly controlled conditions.
It is certainly possible to obtain nutrients from either animal sources or plants. As a fuel source there is good reason to believe fat is optimal, it is transported directly into the blood stream through the lymphatic system, unlike glucose which is carefully filtered by the liver and which attempts to prevent it entering the blood at all by absorbing as much as possible itself first. Nevertheless, carbohydrate CAN act as an energy source for human beings and often does, the body copes. The same applies for all the macronutrients, even fats can be obtained from plant fibre, with the assistance of microbes in the colon, a kind of last ditch nutritional effort before defecation, that in desperate times might make the difference between survival and death.
This is also true of protein. It IS possible for human digestion to work with plant sourced proteins and do the best it can with this second rate material.
But its a bad idea.
Of all the macronutrients that can be obtained from plants, protein is the LEAST desirable. This is for the simple reason that plant proteins are designed for a specific function - to build plants, they are the building blocks of plant cells and structures. Animal physiology is quite different from plant, which means that specific proteins that are very useful for growing plants are TOXIC to humans. This is why it is the proteins in grains and other carbohydrate sources that cause the most problems in digestion. Here is Natasha Campbell-McBride on the topic,
"Mounting research shows that another constituent of grains - plant proteins - is becoming positively dangerous for a growing proportion of humanity : gluten in wheat and other cereals, zein in corn, secalin in rye, harden in barley and avenue in oats." (Vegetarianism Explained p.20)
The extent of the damage these proteins can cause is dependent on the condition of our gut flora, if we are lucky these will offer us some protection. But sub-contracting our body's defence mechanisms to other creatures does not strike me as a very good idea, better to remove the risk by avoiding such items in the first place. This is especially so because there is absolutely NO NEED to use such inferior types of protein, we can obtain much better quality from animal sources.
The main reason for this superiority lies in the proportions of amino acids animal foods contain. This allows us to reassemble them quickly and easily into the proteins we need, because our requirements differ little from those of the animals we have obtained them from, our physiological make up at this level is very similar to their's.
The argument here is simple - we should eat animals because we ARE animals. Nowhere does this apply more than when it comes to protein.
In another post I will respond to Colin Campbell's claim in his 'The China Study' that animal protein, casein in particular, is a cause of cancer. Others have already debunked this idea (see here and here for example). I want to approach his position more from the problems it raises in relation to the scientific method as it is applied in the nutrition field, rather than addressing it in this post. Here I am putting forward a very different kind of argument from his, one that relies more on a form of logic than empirical evidence. There is room for both types of proposition in the debate, but its a good idea to keep them clearly separate. I don't believe Campbell is arguing that we should eat plants because we are plants, so an engagement with his position is not really appropriate at this point. Nutrition debates tend to play fast and loose with these various levels of argument, switching in and out from one to the other. This confuses the issues and often ends up with people talking at cross purposes. It is one ambition of my blog to try and reduce the frequency of this and help improve the quality of the discussion on all sides.