Health, Wellness & Nutrition Blog by Mark A. Mahoney, Ph.D., R.D.N. from Mark Mahoney's blog


 Complementary Protein – A Healthful Addition to Our Diet & Planet

As a follow-up to the 1st Annual North Florida VEGFEST celebrated on April 4th, 2015 at Cascades Park, it seems appropriate to provide some insight into the role of complementary proteins & their role in the  vegetarian diet.

I am well aware of the importance of complementary protein consumption after living/working many years ago in a small village in Ecuador while serving as a Peace Corps Volunteer.  Animal protein was in short supply and legumes and grains were the primary food available.  The purpose of the following blog is to provide some introductory and basic information about complete proteins, with a primary focus on non-meat sources.

It’s often said that individuals who follow plant-based diets are unable to get enough protein in their diet. However this does not need to be the case for your body to thrive and for you to maintain a healthy, active lifestyle, as long as your diet is planned properly. Protein should be high priority in all diets, but especially in plant-based ones. Making sure you have enough protein throughout the day is key to long-term success. A helpful step to remember is to make sure you include a vegetarian protein source at every meal as this will help round out your overall intake of amino acids throughout the day (which are the building blocks of protein). 

What follows is a breakdown of some of the principal different plant-based lifestyle:

**Lacto-Ovo Vegetarianism (consumes both eggs and dairy products)

**Ovo-Vegetarianism (consumes egg products, but no dairy)

**Pesca-Vegetarianism (consumes fish but no other animal flesh--may include dairy & eggs)

** Vegans (abstains from all animal flesh foods and animal-derived products, i.e., honey, dairy and eggs

Although all of these diets have differences, their foundation consists of the same fruits and vegetables, whole grains (or gluten-free grains), healthy fats, and plenty of water.  A good resource for ideas on what to eat in order to ensure you’re taking in sufficient amounts of protein and other often-overlooked nutrients can be found by checking out the Academy of Nutrition and Dietetics position paper on vegetarianism at:

An important theory from the past concerned the belief that vegetarians had to combine certain foods in order to make a “complete protein” or “complementary protein,” something which has proven to be untrue.  In fact, the body is able to store amino acids (i.e., the building blocks of protein) and can be utilized to make up for any limiting amino acid in a vegetarian food.  While it is important to consume a wide variety of vegetarian proteins and foods rich in nutrients through the day, it doesn’t necessarily have to be in the same meal.

Some Basic Facts

ALL plant based foods have varying amounts of protein (plus carbohydrates, fats, other good things), and the body will combine proteins from all sources, to make 'complete protein.' that's true for everybody, veg or non-veg.

The term 'complete protein' means that all eight essential amino acids are present in the correct proportion.

Foods from animal sources have complete proteins - Some foods from the plant kingdom such as soy and quinoa have complete protein.

The term 'incomplete protein' refers to foods which have all the essential amino acids, but are low in one or more of them. That's called the 'limiting amino acid'.

Most plant foods have one or more limiting amino acids which limit the availability of all the other amino acids in food. That's why these foods are called 'incomplete proteins'.

For example, the limiting amino acid is usually lysine (Lys); in legumes it can be methionine (Met) and tryptophan (Trp).  So, the low level of Lys in grains is complemented by a higher level in legumes, and vice versa, to make 'complete protein'.

Animal proteins all contain every single one of the essential amino acids, so they're called complete proteins. If you're an ovo-lacto vegetarian (you eat eggs or dairy products) you can get complete proteins when you eat the eggs or dairy products.

Plant proteins are a little different. Each plant that you eat has a different amino acid profile. For example, grains and cereals

 are extremely low in lysine. In fact, they are so low that they can't even be considered a source of lysine. If you only eat grains and cereals, you won't get enough lysine, and that's bad.

However, legumes such as peanuts, peas, dry beans and lentils contain a lot of lysine -- all the lysine you really need. On the flip side, legumes aren't good sources of tryptophan, methionine and cystine, but those amino acids are found in grains and cereals. As long as you eat some grains and some legumes, you'll get some of each essential amino acid.


Grains and legumes are called complementary proteins because when you combine them, you get all of the essential amino acids. Nuts and seeds are also complementary to legumes because they contain tryptophan, methionine and cysteine.

The following list provides some basic information on examples of some complementary protein combinations:

 Grains and legumes:

**Black beans and rice 

**Pasta and peas

**Whole wheat bread and peanut butter

**Bean soup and crackers

Nuts and seeds plus legumes:

**Roasted nuts, seeds and peanuts

**Hummus (chickpeas and tahini)

**Lentils and almonds

Soy is the one plant protein that contains all the essential amino acids. It's also a good source of         


 fats” and phytochemicals (plant chemicals that may be good for you). It's usually served as tempeh or tofu, and soy milk is a popular replacement for milk. 

Combining Plant Protein Sources -- Bringing it all Together

Protein complementation is combining plant protein sources to achieve a better amino acid balance than either would have alone. Because of differences in amino acid make-up, when plant sources are combined, the strengths of one make up for the deficiencies in another. For example, many grains are notoriously low in lysine, but beans are high in lysine. On the other hand, beans are low in the sulfur-containing amino acids, while grains like wheat contain much of these. By eating beans and grains “together,” the strengths of one make up for the deficiencies of the other, making a source of complete protein.

Two additional resources for those desiring more in-depth information on essential amino acids and complementary protein can be accessed at:

Sufficient to say is that the role of complementary proteins in maintaining a healthy lifestyle as well as a healthy planet is something to be taken seriously.  An ever-increasing population means that eating lower on the food chain may, in fact, be the most obvious choice.  Some food for thought.

Dr. Mahoney has worked in the field of education and health over an extended period in both paid and unpaid positions, inside the U.S. as well as outside. He served as a Peace Corps Volunteer for over four (4) years in Latin America. He has been a Registered Dietitian Nutritionist (R.D.N.) for over 25 years and completed graduate studies in Public Health at Columbia University.

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