Protein Primer – Protein Principles

By Robert Luby, MD

On September 25, City Market is offering a free class entitled “Protein 101.” Dr. Luby offers up some additional information to help you understand the difference between plant-based and animal-based proteins.

Note:This article is not meant as a substitute for proper medical advice. Please consult with your medical practitioner before making any major changes to your diet or using any type of remedy, herbal or otherwise.

In recent years protein has received much less emphasis in the media than fats and carbohydrates.  Together, these three categories of nutrients are known as “macronutrients”.  This is to distinguish them from vitamins and minerals (“micronutrients”).  Proteins are composed of amino acids, 22 of which are considered “standard” amino acids.  Of these 22, nine are considered “essential”.  That is, they are required in our diet because the human species is incapable of synthesizing them.  All living things contain protein, therefore every plant or animal-based item in your diet will contain some protein.  The focus of this article is the main differences between plant-based and animal-based proteins.

The two major advantages of animal-based proteins are protein density and protein composition.  Muscle is highly protein-dense, and the most common animal-based foods (dairy excepted) come from the muscle tissues of animals.  Most animal food sources will contain more protein per weight equivalent than plant-based foods.  Therefore, smaller quantities of meat (and usually calories) are necessary to obtain adequate amounts of protein than plant-based foods.

Protein composition refers to the variety of amino acids contained in any food source.  Animal-based protein tends to contain the entire complement of amino acids, while each plant-based source will lack certain amino acids.  Moreover, in many plant-based foods there are very small amounts of certain amino acids.  This will mean that any strictly vegetarian diet must incorporate a rich variety of items to ensure that the entire complement of amino acids is provided in sufficient quantities.

A major disadvantage of animal-based protein is that one must consider the entire “protein package”, that is, the other micronutrients, macronutrients, and non-nutrients which are contained in the food.  With regards to macronutrients and non-nutrients, meat and dairy usually contain a relatively high degree of fat in general and saturated fat (least preferable) in particular.  This in turn means a higher degree of toxins in animal-based “protein packages” because most toxins are “lipophilic” and tend to concentrate in fats.

Although animal-based protein sources contain important vitamins and minerals, plant-based foods tend to be richer in these micronutrients.  Fiber is another factor to consider.  There is a growing trend to consider fiber as the “fourth macronutrient”.   Fiber is essential for innumerable health benefits, and plant-based foods are far richer in fiber than animal-based foods.

Allergies and food intolerances may also be influential in the choice of protein sources.  The two most common protein allergens are gluten (wheat/rye/barley/spelt/kamut) and casein (cow’s milk).  Other frequent offenders include seafood, soy, peanuts, and tree nuts.  While red meat tends not to cause allergic reactions, its amino acid complement is usually more sulfur-rich.  This can cause a tendency to acidify the body and deplete the body’s natural buffering minerals.  This is one of the plausible mechanisms for an animal-based diet to be more likely to contribute to diseases such as osteoporosis.

Although more research is needed, many studies implicate diets which emphasize animal-based protein as instrumental in the development of cancer and other chronic diseases.  While it may not be solely the protein component of the foods which confers this risk, at least in the case of casein the data is becoming convincing.

In summary, there are advantages and disadvantages to both animal-based and plant-based protein sources.  Rules of thumb to consider are:  1) Consider the entire “protein package”.  Choose lean cuts of unprocessed, organic, grass-fed meat whenever possible.  This will limit many of the disadvantages of animal-based protein sources described above.  Organic free-range poultry and wild-caught cold water fish are good examples.    2)  Moderation in dairy consumption is probably advisable, with preference for organic, grass-fed, and unprocessed items.  3)  A wide range of plant-based foods should be consumed to ensure proper variety and quantity of amino acids.  As with animal-based sources, organic and unprocessed plant-based foods are preferable.