Plant proteins? Yes, please.

What are proteins?

Proteins are molecules composed of at least fifty smaller units known as amino acids. Though many naturalists of the 18th century were involved in studying and discovering these compounds, perhaps it is the French chemist, Antoine Fourcroy, who most deserves mentioning. When this substance was discovered, the scientists were particularly attentive to the coagulation (shrinking of protein) when egg proteins were exposed to high temperatures or to acid. First employed by the Swedish chemist Jöns Jacob Berzelius in 1838, the term “protein” is derived from the Greek “proteios,” meaning “primordial” and indicates their important role in living organisms. In addition to this word, peptides and polypeptides are occasionally used as synonyms.


Why are proteins important?

Proteins represent the source of amino acids for our bodies, from which we can produce other crucial substances, including other proteins. Without these compounds, your body would be unable to grow, develop, or regenerate after injury. There are 9 essential amino acids that our bodies need to receive from the proteins we eat:

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

Through the course of our lifetimes, our protein requirements change. A minimum protein intake of 0.9-1.0g/kg of body weight is recommended daily for children and adolescents. As we reach adulthood, however, this becomes smaller, with 0.6g/kg body weight suggested as the daily requirement. That being said, individual differences exist in our needs and not all the protein you consume can actually be used by your body, so a more realistic daily suggestion is 0.8g/kg body weight for an average adult. Ultimately, this should account for 10-15% of your daily energy input, though should not exceed 20%. Our needs for protein also increase during illness and healing as well as in elderly individuals, with 1.0-1.5g/kg being the recommended daily intake.


Are plant proteins less valuable than those from animal sources?

Among laypeople as well as many nutritionists there is a widely-held belief that protein from plant foods is inferior to those arising from animal products. Let’s dive into this a bit. There are two characteristics to bear in mind when speaking of protein quality: how effectively proteins can be absorbed by our digestive tract and broken up into amino acids that can be passed into our bloodstream, and whether the ratio of amino acids in the specific source meets our needs. Both of these properties are accounted for by the Food and Agricultural Organisation (FAO)’s PD-CAAS (Protein digestibility-corrected amino acid score). The first issue (decomposition of proteins in our gut) is less problematic since the vast majority of proteins (both from plant and animal sources) are readily digested. In most cases, less than 15% of the protein may remain undigested, though in rare cases it may be more. The second issue does provide more of a problem for us. Though our body can synthesise some amino acids on its own, the ones that we call essential amino acids are thus named because they cannot be created in our body and are thus essential in our diet. You can see the “ideal” ratio of amino acids in our table.

Tipe of amino acid

Recommended daily intake of individual amino acids according to the WHO

(mg per kg body weight)

recommended content of each amino acid in consumed proteins (mg / g)

Histidine

10

18

Isoleucine

20

25

Leucine

39

55

Lysine

30

51

Methionine + cysteine

15

25

Phenylalanine + tyrosine

25

47

Threonine

15

27

Tryptophan

4

7

Valine

26

32

 

If any of these acids is lacking, the other amino acids are not used well by the body. The ratio between the use and total amount of digested and absorbed proteins is called the biological value of proteins. The most lacking acid is referred to as the limiting amino acid, since it limits the use of the others. In the table below you can see the amino acid content in some select foods (in percentage according to ideal composition as presented in the previous table). Green denotes amino acids that are significantly lacking in particular foods while blue represents those that have a minimal lack. The second column indicates the total protein content. You can find a more comprehensive table with more foods and a full set of amino acids HERE.

 

Protein content (g/100 g)

threonine

Leucine

Lysine

Methionine and cysteine

Histidine

tofu

15,8

151

138

129

106

162

peanuts

24,4

123

115

68

98

137

beans

8,2

130

155

124

91

139

lentil

9,0

133

132

137

86

156

soya 1

13,0

148

130

117

85

149

soya 2

12,2

161

148

131

118

150

leek

1,5

156

116

102

115

93

broccoli

2,8

116

83

94

94

116

zucchini

1,2

89

107

109

99

119

mânche

2,0

139

121

99

90

100

asparagus

2,2

141

106

93

113

124

buckwheat

11,7

141

114

99

121

129

corn

3,3

147

195

83

115

151

millet

11,0

119

231

38

157

119

barley

12,5

126

124

73

165

125

wheat

13,2

103

124

53

152

150

oats

16,9

126

138

81

171

133

Sunflower seeds

19,3

151

132

81

166

154

lentil + barley (1:1)

11,8

129

128

105

126

141

 

Many kinds of cereal contain relatively low levels of lysine. For example, millet only has a biological value of proteins of 37%. So, if we eat 100g of millet porridge (containing approximately 10g of protein) we will only use about 3.7g for bodily construction and repair while the remaining 6.3g will just be used as energy. Though lysine is limiting in most cereal grains, its deficit is often not as large as that seen in millet and thus has a higher biological value. Wheat, for example, has a biological value of protein reaching 50% while oats and barley reach 75%. Buckwheat reaches an amazing 99%. Unlike the grains, legumes tend to be limited by the amino acids that contain sulfur (i.e. methionine and cysteine). These two acids are interchangeable (you only need one or the other), but this deficiency still makes the biological value of legumes about 85%. The soybean, however, can reach biological values anywhere between 85% and 100% depending on the variety and the cultivation conditions.

Though it belongs in the same botanical family as these legumes, peanuts actually have an amino acid profile much more similar to cereals and display a lack of lysine. This profile is also shared by sunflowers, which fall into yet another botanical family. Fortunately, all hope is not lost; combining two different foods greatly increases the biological value of the proteins you are consuming. For example, by consuming barley (biological value of 75%) and lentils (biological value of 86%), the mixture surpasses 100% use of the protein. The trick here is to combine foods with different limiting amino acids. Teamwork requires individuals with different strengths collaborating to achieve a goal, and this is exactly what you want to aim for with your protein consumption. To make things even better, some vegetables such as leek, broccoli, zucchini, mâche, and asparagus contain reasonable amounts of protein. Not only this, but the biological value of the proteins is also large (over 80%) and have differing limiting amino acids. Combining these foods has you on the right path to protein perfection.


How much protein is found in plant foods compared to animal products?

On average, meat contains about 20% protein (protein content, not biological value of the protein) which is achieved only by a select few high-protein plant foods such as peanuts and sunflowers. That being said, many plant foods have a protein content above 10% (take a look at table 2), so you can get the same amount of protein with a slightly larger amount of food.The answer to our question here though also depends on the method of comparison. Let’s take egg and broccoli as an example. Here we specifically chose an animal food known for its high protein content while also choosing a plant food that is not tofu, seitan, beans, etc. and thus not associated with having lots of protein. Eggs contain 12% protein while broccoli is only 3%. However, if we count the protein content per calorie (this is called the nutritional density) the egg only contains 84mg of protein per Calorie while broccoli sits at 96. Though the protein content of broccoli is 4x lower than in eggs, its nutritional density is greater. This means that in a meal with the same number of calories, broccoli would provide you with more protein than eggs would.


Are there negative effects associated with eating too much protein?

Up to now, we have no direct evidence that excessive protein intake has a negative impact on your body. That being said, there are also no positive impacts. Increasing your protein intake results in more metabolites that your body needs to eliminate, thus leading to more work for your kidneys. Additionally, excessive protein consumption can cause you to excrete more calcium than usual and can thus cause a deficit of this nutrient, thus leading to issues with your bone health and increasing your risk of kidney stones (ouch!). Moderate metabolic acidosis may also occur and there may be some negative consequences associated with the maintenance of your skeletal muscles.


Why is it better to choose plant proteins?

The important thing to remember here is that protein isn’t the only thing you’re putting into your body when you consume food. In addition to other nutrients, animal products (eggs, milk, and meat) also contain many harmful substances such as saturated fats and cholesterol, and in some cases (especially in organ meats) purines as well. In plant foods, however, purines are significantly less present and cholesterol is not present at all. So, next time you’re visiting family and they start giving you a hard time about your protein intake, send them the link to this article! Hope we managed to help you out of that age-old annoyance (and help you get a better grasp of healthy vegan eating along the way).
Thanks for reading, and see you next time!
The Hungry Pumpkin Team


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