Communicating the Protein Content of Plant-based Foods. Opportunities and Challenges

Dr. Kathy Musa-Veloso, Director, Food & Nutrition Group, within Intertek’s Health, Environmental & Regulatory Services (HERS) is a recognized expert, author, and presenter on global scientific and regulatory requirements for health claim substantiation.

Amino acids are the building blocks for proteins; they are strung together in various combinations and lengths, according to instructions in our genetic material, to form all sorts of proteins, including hair, skin, nails, hormones, enzymes, and body structures such as muscle and bone. While the human body is capable of making some amino acids, 9 amino acids (i.e., histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) cannot be made by the human body and are therefore considered essential. These 9 essential amino acids must be consumed from the diet to allow for the normal synthesis of proteins in the body. 
 
Dietary proteins can be consumed either from animal or plant sources. Animal sources of protein include fish, poultry, meat, dairy products, and eggs. Plant sources of protein include legumes, nuts, seeds, grains, soy products, and some vegetables. While there are lots of terms to describe diets that are predominantly plant-based (Table 1), growing in popularity is the flexitarian diet (also referred to as the semi- or demi-vegetarian diet), a diet that is primarily vegetarian with the occasional inclusion of poultry, dairy, meat, fish, and eggs1. This dietary pattern is aligned with the recent recommendations of national scientific authoritative bodies with interests in public health. For example, a “Key Recommendation” of the U.S. Dietary Guidelines Advisory Committee -in their 2015-2020 Dietary Guidelines for Americans- is that a healthy eating pattern includes “a variety of protein foods, including seafood, lean meats and poultry, eggs, legumes (beans and peas), and nuts, seeds, and soy products”2. In Canada, as part of the “Let’s Eat Healthy Canada” initiative, Canadians are encouraged to eat vegetables and fruit, whole grains, and plant-based proteins to reduce the risks of heart disease, type 2 diabetes, and colorectal cancer3. To achieve these dietary recommendations, it is important for consumers to be able to identify plant-based foods that are good sources of protein. Unfortunately, in both the U.S. and Canada, the regulations make it very difficult for food manufacturers and distributors to label most plant-based foods as sources of protein. To understand the dilemma, it helps to first understand the regulations for labeling foods as sources of protein in other key markets, such as the European Union, Australia/New Zealand, and South Korea, and compare these to regulations in the US and Canada, using a mixture of nuts as an example.

Protein Level in Nut Mixture: According to the United States Department of Agriculture National Nutrient Database for Standard Reference Release 28, mixed nuts (dry roasted, with peanuts) contain 19.5 g of protein and 607 kcal per 100 g4; therefore, 12.9% of the energy in the mixed nuts is provided by protein.
 
Protein Claim Requirements in Europe: In Europe, a “source of protein claim” can be made if at least 12% of the energy value of a food is from protein5. Given that 12.9% of the energy value of the mixed nuts is from protein, the mixture of nuts can be labeled and advertised as a “source of protein”.

Protein Claim Requirements in Australia/New Zealand: In Australia/New Zealand, a “good source of protein” claim can be made if there are at least 5 g of protein per serving6. Given that each 30-gram serving of mixed nuts provides 5.9 g of protein, the mixture of nuts can be labeled and advertised as a “good source of protein”.

Protein Requirements in South Korea: In South Korea, a “source of protein” claim can be made if the food provides at least 10% of the protein Nutrient Reference Value (NRV) (i.e., 55 g) per 100 g, 5% of the protein NRV per 100 kcal, or 10% of the protein NRV per serving7. Given that the nut mixture provides 35.5% of the protein NRV per 100 g, 5.8% of the protein NRV per 100 kcal, and 10.6% of the protein NRV per 30-gram serving, the mixture of nuts can be labeled and advertised as a “source of protein”.
 
Clearly, in the European Union, Australia/New Zealand, and South Korea, the eligibility of a food for a protein content claim depends only on the amount of protein in the food. In the US and Canada, the eligibility of a food for a protein content claim is far more complex and depends not only on the amount of protein in the food, but also on the quality of the protein, measured as the “protein digestibility corrected amino acid score” in the US8 and as the “protein efficiency ratio” in Canada9. In both the US and Canada, the measure of protein quality depends on 2 factors:
 

Although nuts contain all 9 essential amino acids and the digestibility of the protein in nuts is fairly good, lysine is present in low quantities, and so nuts do not meet the protein quality criteria required for the protein content claims.
 
There are some circumstances where the protein quality of a food needs to be considered. For example, if the food is a staple for a given population (e.g., rice could be the main source of protein in a developing country), it is important to consider its quality, so that strategies to deliver all essential amino acids in the proper amounts could be generated. Likewise, the consideration of protein quality is very important if the population relies on formulated meal replacements or, in the case of infants, human milk substitutes like infant formula (i.e., the entire diet or a significant portion of it contains a single source of protein). For all other individuals who are generally healthy and have access to a variety of foods, amino acids that are absent or present at low levels in one food can be compensated for by higher levels in another food (Figure 1). For example, peanut butter and whole wheat bread individually do not have a high protein quality, but consumed together (e.g., a peanut butter sandwich), they provide a higher quality protein. Similarly, beans and rice individually do not have a high protein quality, but consumed together, they provide a higher quality protein. So, as long as all 9 essential amino acids are consumed, and as long as they are consumed in sufficient quantities, it does not matter whether they are all derived from a single, high quality protein food, or in multiple foods that, collectively, counterbalance each other with regards to protein quality.
 
Plant-based diets are known to improve health and reduce the risk of all-cause mortality and several cardiometabolic diseases, including, obesity, type 2 diabetes, and coronary heart disease1,10,11. Moreover, it is well-known that plant-based diets (rich in fruits, vegetables, legumes, seeds, nuts, and whole grains) have the least environmental impact in terms of their carbon footprints and are more sustainable than animal-based diets12,13,14. Thus, to encourage the consumption of plant-based foods, as per dietary guidelines and recommendations, perhaps it is time to modernize the regulations related to protein content claims in the US and Canada, and exercise more discretion in terms of when the protein quality of an individual food needs to be considered15.