10 Jun Navigating nutrition on a plant-based diet
Plant-based diets, such as the vegan diet, have gained significant attention in today’s conversation around food sustainability and health. In this Thought for Food article, our PhD student, Patricia Soh highlights some personal nutritional challenges that accompany a plant-based diet and explains the findings from our latest research, which looked at protein quality among New Zealand vegans.
“Becoming vegetarian was easy,” I thought when I made the switch nine years ago. It was an acceptable diet for me, as the taste and texture of meat never quite appealed to me anyway. All I had to do was cut meat and seafood out, and eat more vegetables, more fruit…more vegetarian pizzas, right? …
Within a year though, things got a little less easy. I found myself chronically low in energy and oddly obsessed with chewing ice cubes as if they were a food group. A swift visit to a haematologist revealed that I had developed iron deficiency. Cue the mysterious symptoms solved. “Maybe just some fish?” the doctor gently suggested, but I was reluctant to comply. This left me with the option of either popping iron supplements like post-dinner mints or rethinking my entire approach to meeting my nutritional needs while on a diet that excluded many animal-sourced proteins.
At that time, lentils and beans were unfamiliar foods to me and I lacked the culinary expertise to make them taste good. If these foods had made a constant appearance on my plate, perhaps I would have fared better on my plant-based diet. Nine years later, I like to think I have a better grasp of how to achieve a nutritionally balanced vegetarian diet – it wasn’t just about cutting out meat, but also about learning what to put in its place.
What is a plant-based diet and is it good for us?
Simply put, plant-based diets are rich in foods from plant origin. However, their definition can vary, even within the scientific community. A plant-based diet may range from excluding all animal-sourced foods (as in vegan diets) to allowing dairy products and eggs (lacto-ovo vegetarian), seafood (pesco-vegetarian) or smaller amounts of animal-sourced foods in the everyday diet. Globally, the shift towards plant-based diets is gaining momentum, and possibly driven by factors such as environmental sustainability beliefs, animal-welfare, health concerns, food intolerance or allergies, and cultural or ethical beliefs. Regardless of the motivation, meeting all nutritional requirements is a non-negotiable aspect of long-term dietary success. Undeniably, consuming sufficient servings of vegetables, fruits, and legumes is an important part of a healthy diet. Yet, achieving nutritional adequacy becomes challenging with the exclusion of multiple food groups. A strict plant-based (vegan) diet significantly narrows the range of foods that offer high-quality protein and micronutrients. This means that a vegan must either consume larger quantities of select foods – navigating the challenges of increased energy intake and the satiety effects of high dietary fibre – or adopt a strategic and informed approach to combine complementary plant proteins to meet nutrient needs.
Protein quality in vegan diets
Among the essential nutrients to consider, protein quality stands out. This refers to the amount of available amino acids that the body can absorb and use. While getting “enough” protein is important, it’s the quality of the protein that we must focus on due to the direct metabolic functions of each amino acid in our body. Protein quality is an important consideration in more restrictive plant-based diets as plant-sourced foods are known to have more variable and lower quantities of utilisable amino acids as compared to animal-sourced foods.
How do New Zealand vegans fare in terms of protein and amino acid intake?
Is there evidence that vegans don’t meet their total protein requirements? Findings from two systematic reviews and an observational study suggest that while total protein intake among vegans is generally lower than that of omnivores, it is not necessarily below daily requirements. Therefore, yes, vegans are likely able to consume sufficient protein from their diets to meet bodily requirements. We also observed sufficient total protein intake among three-quarters of the analysed vegans residing in New Zealand.
The key benefit of protein consumption is the provision of amino acids, such as lysine and methionine, which have specific functions in the human body, from protein synthesis, muscle maintenance, and immune support to homeostatic and enzymatic functions. Protein quality varies substantially even among plant-based foods. For example, 100g of cereal grains provide lower quantities of digestible lysine, but higher quantities of methionine, whereas 100g of legumes in the form of soybeans provides the reverse profile. Thus, within a vegan meal, overall protein quality can be improved by consuming cereals and legumes together – a classic example of protein complementation.
Long-term depletion of indispensable amino acids (IAAs) – which the body cannot synthesise – can lead to negative health consequences. In severe cases, and especially amongst the elderly, muscle atrophy and sarcopenia can occur as the body’s response to protein intake is diminished with age. While deficiencies in these nutrients may not cause immediate discomfort, their effects can accumulate over time, negatively impacting health and quality of life. Considering the importance of amino acids for physiological functions, we were more interested in understanding the protein quality of vegan diets by comparing the quantity of digestible IAAs obtained from the diet to the daily requirements.
Our results showed that many individuals had insufficient intake of two amino acids: leucine and lysine. This is a cause for concern, so efforts need to be in place to improve their quantities in a vegan diet.
It can be tricky to improve protein quality while balancing energy restrictions. Legumes and pulses, as well as nuts and seeds, provide higher amounts of protein and several essential amino acids compared to grains for the same amount of energy. This suggests the importance of incorporating legumes, pulses, nuts and seeds in addition to grains in every vegan meal. Hence, ensuring diverse sources of plant foods would increase the likelihood of a vegan meeting the daily requirements for total protein and protein quality.
Therefore, instead of just a veggie pizza with salad leaves as topping, maybe add some tofu and beans to the meal as well. But nowadays, we can go beyond traditional protein sources. Compared with nine years ago, consumers are offered a wide selection of novel plant-based alternatives, from soy-based patties to protein powders and dairy alternatives. It is likely that the veggie pizza could be sprinkled with plant-based sausage. The question is, how much of these novel foods should we consume in our diet, and is it a good idea to replace traditional plant proteins with them? The processing techniques used in these novel alternatives do have beneficial impacts in increasing protein digestibility and utilisation by the body. Formulations in these foods may also include fortification with minerals and vitamins potentially lacking in traditional vegan diets. Hence, these foods may provide ease in bridging nutritional gaps, especially for individuals first transitioning to a plant-based diet, or quick meal options in a busy modern lifestyle. Despite this, elevated levels of sodium, saturated fat and other additives in these foods may be of concern, especially if they are consumed frequently.
Take-home message
Dietary choices are personal and largely based on how acceptable foods are to an individual. Several other factors such as cost and cultural or religious practices also play important roles. Diets need to be health-promoting, particularly in their ability to meet all nutritional requirements from the foods consumed Shortage of nutrients like lysine, leucine, iron, calcium and vitamin B12 – deficiencies commonly found in vegan diets – have long-term health consequences, reduce productivity and diminish the quality of life. Certain populations like the elderly, young children and women of reproductive age require special care from dietitians and health care professionals if a vegan diet is followed.
A well-planned vegan or vegetarian diet can meet nutritional needs, but this requires intentional effort and adequate nutritional knowledge to incorporate a diverse range of plant-based foods. Fortunately, a growing variety of food options — along with improved formulations and fortified products — makes it easier to narrow potential nutrient gaps. Research in these areas of food science and technology will continue to grow alongside the rising interest in plant-based diets and will provide support to individuals who wish to make this dietary transition. In some cases, targeted supplementation, such as vitamin B12, may be necessary to ensure adequacy, particularly in more restrictive diets.
It’s taken some learning for me, but I think I have mastered the ins-and-outs of a plant-based diet. Still, I keep an eye on my iron and omega-3 levels and ensure legumes and pulses are part of my everyday meals which thankfully, no longer include ice cubes!
This Thought for Food was written by our PhD student, Patricia Soh, with the support of the SNi team.
