I have to exercise in the morning before my brain figures out what I’m doing. ~ Marsha Doble

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Well, if you are expecting a humorous post by B on redefining protein as she did veggies and legumes, read no further. This post is dreary as it gets! In Caloric and Protein Needs we had noted that all the protein needs can be met from plant based sources. While delving deeper into this topic, we found answers to a variety of common questions. We knew some of what is listed here, but quite a bit was news to us.

What is protein? Why should one care?

Protein, next to water, makes up the largest portion of our body weight, since it is contained in muscles, organs, hair, etc. Proteins regulate body functions and brain activity through enzymes and hormones.

There are 22 amino acids which make up protein (there are couple of amino acids which are not building blocks of protein). The liver synthesizes about 80% of these during the metabolic processes, but the remaining must be supplied directly by diet, and these amino acids are referred to as the essential amino acids.

There are a set of nine essential amino acids (leucine, isoleucine, histadine, valine, methionine, lysine, phenylaniline, threonine, and tryptophan) The human body cannot manufacture these essential amino acids. They have to be consumed and absorbed from food.

Is plant protein incomplete?

No. This is a misnomer. Plant protein is of lower quality than animal protein because most plant foods (soy is an exception) have a limiting amino acid that reduces the efficiency of usage for muscle regeneration.

What is a ‘limiting amino acid’?

The amino acid that is in shortest supply in a foodstuff is called the limiting amino acid. Our body requires a certain proportion of each of the essential amino acids. Foods that have all the essential amino acids in the required proportions are called high quality protein. Animal sources like eggs, dairy and meat provide high quality protein.

Among plant foods, soy is considered a high quality protein. Others are spirulina, quinoa, hempseed, amaranth and buckwheat.

All other plant sources are low on one or the other essential amino acids. Typically cereals / grains are lower in lysine and beans are lower in methionine. Protein complementing helps correct this imbalance.

How does protein complementing work?

Plant sources - and even strict vegan diets - can provide all dietary requirements, provided they are based on a VARIETY of whole plant foods. Some believe that careful monitoring of nutrient levels is important in strict vegetarian diets, but there are virtually no cases of protein-deficiency among populations consuming adequate calories. The only common cases of protein-deficiency occur among populations that are chronically undernourished.

The net protein utilization is profoundly affected by (and somewhat affected by) salvage of essential amino acids in the body. It is therefore a good idea to mix foodstuffs that have different weaknesses in their essential amino acid distributions. This limits the loss of nitrogen through deamination and increases overall net protein utilization.

Mixing grains, pulses, seeds, nuts and vegetables will create high quality protein. Many cultures have dietary habits that reflect such combinations - rice with lentils/beans/peas, pita bread and hummus, beans on toast, peanut butter sandwich, muesli with milk are all common examples of protein complementing.

Do vegetables have any protein?

As a percentage of total weight, vegetables are low in protein (water accounts for a lot of their weight). But as a percentage of calories the story is quite different. If you eat a 100-calorie serving of asparagus, 40 of those would be from protein. Broccoli has 20% and green peas contain 25% caloric protein.

What determines protein quality?

Presence of essential amino acids and digestibility. If one or more of the essential amino acids is limiting (present in a low amount) then the required protein intake is higher. This is the same for poorly digested proteins. Detail from one study can be found here. In general, soy is better than peas, which are better than beans and lentils. Whole grains are better than refined grains and cereals. The bio-availability of these foods can be increased by complementing the food with sufficient fiber.

Does every meal need to contain a balance of essential amino acids?

No. Plant foods can be combined and complemented over a 24-hour period to achieve high quality protein.

What happens when excess protein is consumed?

This is a tricky one. There are positives and negatives. A popular myth in our times is that consumption of a lot of protein will lead to a healthy life. While it is true that deficiency of protein results in low muscle mass especially for athletes, excess protein has side effects. The main positive (esp for vegetarians and vegans) is that the limiting protein is no longer limiting in amount for muscle tissue synthesis as there is enough to go around. However, the non-limiting proteins are far in excess and will get converted to energy, and if caloric needs are exceeded these will get converted to fat. (J Agric Food Chem 1981;29:429). Tons of studies also show that excess protein consumption increases osteoporosis. John Robbins makes this case in his book Diet for a new America.

What is the relationship between pH and type of protein?

Blood needs to be at a pH of 7.4 for ideal oxygen absorption and a host of other chemical reactions. In fact, if the pH gets as low as 6.8 death can occur. During strenuous exercise, the body’s metabolism exceeds the supply of oxygen and other reactions kick in to bridge the gap. Lactic acid is a by-product of these reactions and this enters the blood stream causing a reduction in the pH. The body has buffer mechanisms to counter this pH change. In addition, the body taps into the calcium in the bones to provide part of the pH balance.

Meat and dairy based protein is typically acidic and does not help the cause. On the other hand, all vegetable protein is alkaline and aids the natural processes in the body and also reduces the loss of calcium from bones. The question of dairy protein, especially milk is very interesting - is it helpful as a calcium source? or hurting as a protein source? - and will be reserved for another post!

Good references

An excellent book (available free online) from the Food and Nutrition Board is this Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients)
The USDA database has nutrient information for thousands of foods.
For a summary view of common plant proteins go here.

Oh, BTW - Where do you get your protein?

In the fresh and dry produce aisle of the grocery store

- Jai

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amino-acids, fitness, myths, NUTRITION, plant protein, protein, vegan, vegetarian, Vegetarian Athlete

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