A large number of reliable studies has shown that official diet recommendations tend to be twisted to the benefit of the animal industry. Animal products are praised as healthy and essential while a vegan diet is branded as deficient.
According to "experts" they lack the essential quantitative and trace elements iron, zinc, calcium and magnesium. These minerals are essential for certain metabolic and growth processes of the body. Such allegations can, however, be quickly refuted by comparing different tables of nutrients. Unfortunately, very few do so but, instead, they blindly trust official statements.
To one's great surprise, one will find out that all the above mentioned elements are contained at least at the same degree and often in far higher concentrations in vegetable food. The only exceptions are the iron content of black sausage and kidney or the zinc content in oysters and other shellfish. But these types of food do not play any role in the daily supply of nutrients as only very few people eat them daily.
If you compare the figures, you will find out that it is absolutely no problem to take these nutrients in a sufficient degree from a purely vegetal diet. It would on the contrary be very difficult or even impossible to take in sufficient zinc and above all magnesium in an animal-based diet – not to speak of roughage fibres and certain vitamins that do not occur at all in animal products. Admittedly, iron of animal origin can be better absorbed by human digestion but if the food contains vitamin C (e.g. in vegetables, fruit and juices), this flaw can easily be compensated for vitamin C helps the resorption of iron.
People often wonder how vegans can cover their requirement of protein. Together with minerals and vitamins, proteins, carbohydrates, fats and roughage fibres are the essential components that we need to take in every day.
The average energy requirement of 2,600 kcal should be covered by 55% of carbohydrates, 30% of fat and 15% of protein. http://thescienceofeating.com/food-combining-how-it-works/calories-fat-carbs-protein-per-day/
With a fairly balanced vegan diet it is no problem to take in sufficient carbohydrates and fats. Vegetable fats have in addition the big advantage that they occur far more often in the healthy, unsaturated form and do not contain cholesterol. But it is often claimed that vegans have problems in reaching the recommended daily amount of 60-100 g of protein.
A look at nutrition tables to find out the protein contents of typical vegan foods will show that this allegation, too, is totally distorted. The protein content of some vegetables is even higher by far than that of animal origin.
Meat consists at a degree of 15-20% of protein on average, with fish it is 20-25% and some sorts of cheese reach up to 30%.
Vegetable sources of protein:
So there are many excellent plant based sources of protein, all free from cholesterol, carcinogen proteins (cf. Studies) and free from too many saturated fatty acids.
But in spite of the undoubtable evidence there still are people who think they know better and put forward another prejudice: "Vegetable protein is not as easily exploitable as animal protein." This statement, too, is based on superficial knowledge.
But one thing is true, however: not all proteins can be equally exploited by the organism. This is due to the components of proteins, amino acids. There are eight essential amino acids, which the organism cannot synthesize itself and which have thus to be supplied via food.
Wheat proteins have a different amino acid structure than soy proteins. If the two are consumed separately, our food lacks some of the eight essential amino acids and the protein cannot be well exploited. But if the two are combined in a meal, e.g. corn (pasta) with soy (tofu), the amino acids complement each other and the protein we take in is exploited more effectively. This is what is called biological value of proteins. A valency of 100 means that 100% of the intake of protein can be transformed into endogenous protein.
Egg protein ranks on top and has a natural valency of 100. Next come potatoes with 96%. Beef, cow milk, soy and rice are in the same division and reach 82-88%. Pulses, cereals and nuts have slightly less exploitable protein and reach 59-73%.
But as most meals contain a combination of diverse proteins (e.g. bread with a lentil-potato soup), a biological valency of 100% is usually attained or even exceeded. You can find a detailed table under: http://www.fooducate.com/app#!page=post&id=54637528-C22F-288D-4494-86B7BD5B9737
So the argument that plant bases protein can only be badly exploited is unjustified.