Proteins in the Diet - Part II

15.10.2019
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Proteins in the Diet - Part II

Biological value is not equal bioavailability

As respects the quality of protein, you must consider several factors. The biological value is not equivalent to bioavailability because this can increase or reduce the value, so it is also crucial.

The combination of the different food groups serves to better supply with all necessary components (nutrients). This also applies to the amino acids; the composition can complement and enhance the value and the bioavailability. 

More information: The biological value expresses the content of the essential amino acids (protein synthesis components); the bioavailability results from different conditions of the absorption and metabolism. Bioavailability depends on binding conditions, inhibitors, processing, food combinations, and other factors. There is a wide variety of data on the biological value of proteins in foods. The values ​​vary depending on the measurement methods. Even meat protein bioavailability (e.g. level 85%) and thus its biological value may be reduced. Fish proteins are examined to be more digestible and more bioavailable (98-99%). Cereal and Corn protein have high bioavailability (90-95%), but the value is reduced because of some suboptimal amino acid contents.

An increase of the biological value above 100 is possible by combining food (e.g. 36% whole egg plus 64% potato = protein value 136). Even with the of the right combination of plants, one can reach a protein value over 100 and thus optimal supply (55% soya plus 45% rice = value 111). It must be emphasized that one must not only consider the biological value, but also the bioavailability, which may depend on different processing conditions. For the “Protein Digestibility Corrected Amino Acid Score”, soy protein is good as well as egg protein (both show the optimal highest value).

Of the plants, the vegetables* and seeds contain a relatively high proportion of protein with good biological value (*soya is the highest). Legumes like beans, however, also contain antinutrients (see below) which reduce their digestibility. Therefore, the preparation methods and the type of legumes play a slightly higher role than in other vegetables.

Soy and soy products (like tofu) and quinoa contain all the essential amino acids. Although they do not always provide the same high levels and bioavailability for all essential amino acids as some animal proteins, they are always a near-perfect source of nutrition in the vegan diet.

Soy products (organic quality) are very good. For example, 100g of soy flakes contain almost 45-69g protein. Specially made “protein-bread” (made or complemented with vegetable flour) can also provide a relevant amount of protein in bread - otherwise bread (including full-grain bread) has a relatively low protein content.

Amaranth and quinoa provide a higher protein content (12-15%) in the group of cereals. Muesli of whole oats can be upgraded with seeds, nuts, and these two-grain types. Bread should consist wholegrain of sourdough with seeds and it can be upgraded with a proportion of legume flour for the proteins and more phytochemicals. Also, coconut flour with about 21g protein / 100g well contributes to the protein content.

Especially with lentils and beans, the bioavailability depends on their antinutrient* content. White beans and pale-colored lentils contain fewer tannins which reduce the digestibility and thus the availability of some amino acids. The bright varieties thus provide more digestible proteins. However, this does not make the other varieties less valuable, because food also depends on the variety of compounds (especial phytochemicals) and not just on macronutrients.

*Antinutrients are natural food ingredients such as oxalic acid in spinach and beetroot, etc.; inhibitors of some digestive enzymes (e.g. protease inhibitors in legumes) which inhibit the digestion of proteins; or phytic acid in nuts, seeds, and whole grains, which reduces the absorption of magnesium, calcium, iron and zinc.

With a good combination of foods, the antinutrients are irrelevant; e.g. the proteins are also absorbed more than necessary from legumes. Even regarding the micronutrients, in healthy conditions and balanced nutrition, despite the antinutrients, you will have no deficiency supply.

Manufacturing the processes and bioavailability of proteins

The processing and treatment of foods high in protein may result in positive or negative changes concerning the bioavailability of the protein and its biological value. Protein value is partly reduced in foods when exposed to strong heat (for example, with high heated milk or isolated soy protein).

In milk and soybeans today, usually no longer denaturation by prolonged high temperature or chemical treatment is used for preservation, but processes that allow pasteurization under very high pressure and lower temperatures. This significantly reduces quality losses. The process of very short ultra-high heating of only a few seconds with subsequent immediate cooling to about 4 ° C spares the proteins.

Heating does not always worsen bioavailability. Boiled eggs have by the heat-related denaturation of the protein higher bioavailability of their proteins compared to raw eggs.

Overall, as with almost all foods, that even with soy and milk, the gentle processing is beneficial. However, even with some adverse processing, the abundant food supply in our cultures usually does not result in a lack of essential amino acids when you have a balanced and diverse food selection.

Summary recommendations for protein supply

It makes less sense to focus solely on the single components or single values, such as the "biological value" of the proteins. The diverse and balanced combination of different foods is always more useful for the good supply of proteins and many other nutritional factors (protective substances).

For the supply of all the necessary essential amino acids (protein synthesis components), you need neither fish or meat, nor milk or egg products, but it must be noted that it is harder for vegans to provide themselves with all the synthesis components. For ovo-lacto-vegetarians or lacto-vegetarians, however, it is easy, to provide the essential amino acids well, when they have a good food combination.

The combination of plant foods with dairy or egg products increases the biological value of proteins above 100 reference value for the supply of all necessary protein components.

See the graphic at appendix

  • A balanced diet with the consumption of plants (base of the pyramid) with milk *, egg **, fish, meat *** and products made from it facilitates the coverage of the protein requirement.
    Reduce saturated fats:
    * the best low-fat dairy products;
    ** for the proteins in egg, only the egg white is good;
    *** in a larger context fish is better than meat and for meat, the best is low-fat poultry meat.
  • A sufficient supply of protein is also possible in a vegan or vegetarian diet if a varied food selection exists.
  • Of the plant foods, the vegetables * and seeds contain a relatively high proportion of protein with a higher biological value (* soya highest). They provide plenty of proteins and should be included frequently in the diet.
  • Some legumes, however, contain antinutrients (inhibitors) that make their digestibility a bit more difficult. Therefore, the preparation methods and the type of legumes play a slightly higher role than in vegetables.
  • But soya achieves the same optimal levels of digestibility and thus bioavailability as the egg.
  • In cereals, especially amaranth and quinoa provide higher protein content compared to other grain. Muesli can be enriched with oats, seeds and these two-grain sorts in addition to whole oats.
  • Bread should consist of sourdough whole grain with seeds and it can be enhanced for the proteins with a proportion of legume flour, amaranth or quinoa as well as coconut flour. You can buy baking mixtures, which have predominantly protein components and "fiber" at very low carbohydrate levels.
  • Add amaranth, quinoa, dried coconut pulp, and legume powder to smoothies for a portion of protein.
  • Nuts, seeds and whole grains and dried mushrooms provide an additional good protein contribution.
  • Pay attention to the balance between proteins and carbohydrates. Prefer foods with not predominantly fast carbohydrates but contain a good mix of carbohydrates and proteins, which makes “slow carbohydrates”.

In phases of growth, after illness or injury, as well as in competitive athletes, although the protein requirement increases to almost twice the recommended daily protein intake, this quantity is already covered by the quantitatively larger food intake, when you have a balanced diet.

Resume: In the diet of our cultures is a sufficient protein supply, often it is even too high, so it lacks neither sufficient biological value nor sufficient bioavailability. A potentially low value is compensated by the already quantitatively high amount of proteins in the daily diet. Only in a very unbalanced diet, which contains almost only fast available carbohydrates (pasta or pastry from white flour, confectionery, potato, rice, etc.), it comes in our cultures to protein deficiency. Since protein sources from animal products often contain more potential harmful saturated fats, it is better to consume more protein-rich plants.

The protein requirement for infants and children was previously considered too high. In an extra newsletter, the topic of protein needs in pregnant women, breastfeeding, and infants, as well as children and adolescents in the growth phases, is posed.

The subject of proteins in sports will be debated in another newsletter.

Prof. Dr. Werner Seebauer is Dean of Studies – Association of German Preventologists, Head of Preventive Medicine Department of Institute of Transcultural Health Sciences (European University Viadrina) and Head of Preventive Medicine – NESA (The New European Surgical Academy). Since 2000, prof. dr. Werner Seebauer worked only in preventive medicine, after ten years spent at the Frankfurt University Hospital. He is also involved in the medical professionals training for nutrition and prevention.


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