Posted by kathryn in Kid's nutrition, Protein and Q & A Thursday

Question number one, for this week’s Q&A Thursday is from Keltie:

Our family is vegetarian and I’m currently breastfeeding. I’m worried about my protein intake and also protein for my baby once he starts on solids. how do I ensure we are getting enough?

Protein is important for all of us. While it’s one of the nutrients vegetarians need to be careful about, in clinic I also see many omnivores who are not eating enough protein. Keltie, I’m going to answer your question in two posts, as there’s a lot of background to cover. The first post is more generally about protein and about vegetarians. While I’ll move onto your specific concern about breastfeeding in the second post.

Why do you need protein?

Protein is important to all of us. If forms part of the structure of your body. Your hair, skin, nails, muscles, brain, heart, lungs, liver and so on, are all made up of protein. Protein is also used to mend tissue, grow new tissue and make new cells.

In addition to this, most of the enzymes that catalyse your body’s biochemical reactions, are made of protein, along with the immune system factors that protect you from disease. Without an adequate intake of protein all these body parts and processes suffer.

Amino acids

Proteins are made up of smaller units called amino acids. There are about 20 amino acids and these join together, in a variety of sequences to form all the different proteins you need.

Amino acids are split into two groups, essential and non-essential amino acids. This is slightly misleading terminolgy, because we need all of the amino acids for our bodies to function adequately. However, the non-essential amino acids can be manufactured by the body. The essential ones are so called, because we must obtain them from our diet .

There are eight essential amino acids: valine, leucine, isoleucine, phenylalanine, tryptophan, threonine, methionine and lysine.

Sources of protein

The main sources of protein are meat, fish, dairy foods, legumes, nuts, seeds, eggs, grains. Most people don’t realise grain foods, such as bread and pasta, contain protein. While they are mostly carbohydrate, for vegetarians these foods are an important part of total protein intake.

As humans we need a certain ratio of amino acids to match our needs. However, not all the above foods contain sufficient amounts of each of the eight essential amino acids. Those foods that closely match our requirements are said to have a high biological value (HBV), while those with insufficient amounts of one or more of the essentials are said to have a low biological value (LBV). Most animal foods (meat, fish, eggs) are HBV, while plant foods tend to have a LBV.

Vegetarians and protein

To counter-act the LBV of most plant foods and ensure an adequate intake of all the essential amino acids, vegetarians need to eat a variety of protein containing foods.

The idea is that by using different sources of protein you counter-act the amino acid deficiencies in each food and increase the overall protein value of your meal, with an amino acid spectrum that much more closely matches your body’s needs.

For example legumes have lots of the amino acid lysine but are low in methionine. Whereas grains are high in methionine and low in lysine. Separately their use is limited, but when combined each makes up for the lack in the other and overall provides a much more useful protein meal.

I find it interesting that people in many traditional cultures have been protein combining long before the nutritional significance was understood. Just think of dal and rice, hummous and flatbreads, tofu and noodles, beans and corn tortillas.

How much protein do you need?

For adults, the recommended daily intake of protein for men is a minimum of 0.84g of protein per kilogram of body weight. For adult women (who are not pregnant or breastfeeding), the RDI is a minimum of 0.75g per kilogram of body weight.

Therefore a 60kg woman would need 49g of protein each day, while a man of the same weight needs 50g. Whereas a 90kg man needs 76g of protein and a woman would need 68g.

Note that people who are very active, women who are pregnant or breastfeeding, and people over 70 need more protein.

Protein content of typical foods

• 100g meat, chicken or fish – 20g protein
• 2 eggs – 12g protein
• 10 almonds – 2g protein
• 250ml milk – 8g protein
• 200g tub yoghurt – 12g protein
• 100g cooked beans – 6 – 8g protein
• 100g tofu – 12g protein
• 100g cooked lentils – 5g protein
• 1 cup cooked pasta – 6g protein
• 1 slice bread – 3g protein

28 June, 2007