Plant Based Health Special Series: Vegan diets and protein

By Dr Mikki Williden

While I’m an advocate of a whole-food based diet that includes animal protein, there are people who may do really well on a vegan diet (a diet that excludes meat). For most, though, there are nutritional considerations of excluding animal protein that I want to raise awareness of, and some practical ideas as to how to correct these so you (or someone else you know who may be following a vegan diet) can optimise their protein intake.

 

Protein Quantity

One of the main questions that those following a plant based approach get asked – and it’s a good question! While most plant based advocates insist that getting protein in their diet is a non-issue, I would argue that that isn’t the case – even though protein is in a wide variety of foods, plant and animal based, people still struggle to meet their recommendations- this is true of both omnivore and plant-based alike. The most recent adult nutrition survey (ANS) showed an average of 73-79g of protein was consumed by women aged 19-51 years. While we don’t have good New Zealand data, international literature consistently reports that people following a plant-based diet consume up to 30% less than their omnivore counterparts. This may be because it takes a considerably larger number of calories (and therefore food) to get the same amount of protein that would be found in animal-based foods, which can be tricky for females who may not have a large appetite.

The recommended daily intake according to the New Zealand Dietary Guidelines is 0.8g per kg bodyweight of protein, which would place the amount reported from the ANS within range. However, the nutrient reference values (NRV) document, a resource created by both Australian and New Zealand Government experts has an acceptable macronutrient distribution range (ADMR) of 15-25% of daily calorie intake coming from protein. This places protein requirements much higher, and is more in line with academics who research protein needs for populations and advocate for levels of approximately 1.5g per kg body weight for optimal health outcomes. The discordant recommendations come from a new understanding of protein’s role in many areas of the body such as the regulation of body composition and bone health, gastrointestinal function and bacterial flora, glucose homeostasis, cell signalling, and satiety. The RDI of 0.8g per kg bodyweight was based just on nitrogen balance and protein turnover. If we consider an ‘average’ weight of 68kg for females, putting their protein intakes at around 102g, of which 90% of the population fall below adequate intakes if we consider the ANS data.

 

Protein Quality

It’s not just quantity that is an issue –the quality of protein that also needs to be considered. Protein-containing food provides 22 amino acids to the body, 9 of these are considered essential or ‘indispensable’ – they can’t be produced by the body and must be provided for in the diet. All animal based sources contain these 9 essential amino acids, however vegetable sources of protein (including nuts, seeds, legumes, flours, vegetables) are missing at least one of them. Further, assessing quality historically didn’t consider indispensable amino acids beyond their ability to synthesize protein and its metabolites.  Now, experts agree we need to also account for protein’s role in the many other functions I listed earlier. There is also increased recognition that digestibility of protein needs to account for the presence of ‘anti-nutrient’ factors present in plant-based foods. This has led to the creation of a new method that assesses protein quality (called the Digestible Indispensable Amino Acid Score (DIASS) to replace the older Protein Digestibility Corrected Amino Acid Score (PDCAAS) – yes, both mouthfuls to say! When comparing plant versus animal protein sources using PDCAAS, some proteins were rated almost equal in their quality, (for example soy and whey protein). Now, though, the DIASS reduces the plant-based proteins by a considerable amount due to the presence of phytic acid, trypsins and alpha-galactosides in nuts, seeds and legumes which reduce digestibility of protein and other mineral absorption.

 

So how much of a problem does this pose? It’s difficult to say; many of the potential pitfalls here may not be apparent in the short term and could take years to develop. Research investigating the relationship between amino acid content of a vegan diet and the association between gastrointestinal function, gut microbiome and glucose homeostasis hasn’t been conducted over the long term in clinical trials, so we can’t establish risk. And environmental and genetic differences in every body mean that what we see as problematic for one person may be the reasons another person thrives. Short of introducing animal protein, my advice for all is to make protein the first nutrient you consider. While it may not be in the most bioavailable form in most plant based forms, ensuring a variety of whole grains, legumes, nuts and seeds will help people increase the variety of amino acids needed for optimal health and keep protein levels high.

  1. Quinoa is a pseudo-grain that has a higher protein content than most grains and makes it a good, gluten free choice for many people.
  2. Soaking any grains may benefit from adding an acid medium (such as apple cider vinegar) to help break down the phytic acid.
  3. Edamame beans (soy beans) and fermented soy (such as miso or natto) are complete protein sources and are either minimally processed or are produced in such a way that helps reduce the anti-nutrient factors present in legumes
  4. A grain bread that is made from soaked and sprouted grains (such as buckwheat, for example) will have more bioavailable nutrients than other types of bread. Essene bread is a good example of a bread that is available through health food stores and is made from soaked organic rye or wheat
  5. If preparing own legumes, ensure you soak for at least 12-24 hours, with traditional cultures recommending adding a pinch of bicarbonate of soda to the water for kidney-shaped beans – this is said to reduce the cooking time considerably. For other legumes (such as black beans), soaking in water (with or without a tablespoon of apple cider vinegar for each cup of legumes). Refresh the water every few hours to help enhance the digestibility.
  6. Soaking nuts such as almonds, pecans and walnuts for 12-18 hours and then drying out nuts in the oven at low temperatures for a long time (100 degrees for 6-8 hours) will enhance the absorption of nutrients, including protein, from these.

A final word on the emerging number of meat-substitute products out on the market. Some, such as the Sunfed range you will find in the freezer section of the supermarket, are made with pea protein and have minimal ingredients. These are some of the higher protein options out there. Other substitutes are made predominantly of wheat, contain vegetable oils, additives, flavours and colours, are low in protein, and are effectively more ‘junk’ foods than quality substitutes for people wanting to maximise their plant-based diet. Make it a habit to check the ingredients list before deciding to purchase or relying on these as a substitute for animal protein.