Plant based diets

Plant-based diets are growing in popularity across the UK, but they require careful nutritional planning. This article covers the key macronutrients and micronutrients to consider — including protein, omega 3, vitamin B12, iron and calcium — and how to supplement effectively on a vegan or vegetarian diet.

Plant based diets

What are Plant-Based Diets?

A diet rich in plant foods can be defined as a 'plant-based diet' and may also limit or completely exclude animal products. There are many variations of plant-based diets which lie on a continuum regarding how much or how frequently animal products are consumed.

Type of Plant-Based Diet Principle Components
Vegan Excludes all animal products; exclusively plant foods.
Lacto-vegetarian Excludes meat, poultry, fish and eggs; includes dairy.
Ovo-vegetarian Excludes meat, poultry, fish and dairy; includes eggs.
Lacto-ovo-vegetarian Excludes meat, poultry and fish; includes dairy and eggs.
Pescatarian Excludes meat and poultry; includes fish and seafood. May or may not consume eggs and dairy.
Flexitarian Primarily plant-based; mostly excludes meat and fish but allows occasional consumption.

Healthy vs Unhealthy Plant-Based Diets

Plant-based diets have gained considerable attention for their potential health benefits; however, not all variations are inherently health-promoting. The quality and quantity of foods consumed play a critical role in determining health outcomes. For instance, refined grains and sugar-sweetened beverages are less nutritious plant-based choices that do not provide the same health benefits as minimally processed wholegrains, fruits, and vegetables.3

As with any dietary pattern, prioritising healthy and balanced eating is essential. For those following a plant-based diet, this involves focusing on health-promoting foods such as fruits, vegetables, dairy or fortified alternatives, wholegrains, and legumes, while consuming high-fat, salt and sugar foods less often and in smaller quantities.

Macronutrients

Macronutrients are essential to health and specific attention must be paid to ensure adequate intake from plant sources. Compared to omnivorous diets, plant-based diets are typically higher in carbohydrates, dietary fibre and omega-6 fatty acids, but lower in protein, saturated fat and omega-3 fatty acids.4

Protein

Vegetarian and vegan diets have the potential for reduced protein intake, requiring careful planning to ensure adequate consumption of plant-based protein sources such as legumes, soy products, wholegrains, nuts, seeds, and plant-based protein powders if required (such as pea protein). Variations of vegetarian diets can also receive protein from eggs and dairy.

Plant proteins generally have lower digestibility than animal proteins.5 Digestibility is measured using the Protein Digestibility Corrected Amino Acid Score (PDCAAS) or the Digestible Indispensable Amino Acid Score (DIAAS), with animal proteins typically scoring higher due to better digestibility and higher concentrations of essential amino acids.6

Reduced digestibility can be attributed to higher levels of anti-nutritional factors (ANFs) in plant proteins.7 Common ANFs include tannins, phytates and lectins, but cooking, soaking, and boiling can diminish these factors, enhancing protein digestibility.

While plant proteins can provide all essential amino acids, they often lack one or more (most commonly lysine). Vegans can achieve a complete protein by combining wholegrains with beans or pulses, or by pairing wholegrains with nuts or seeds. A varied diet including different plant protein sources can help ensure a complete amino acid profile.

Carbohydrates

Unhealthy plant-based diets can be rich in refined carbohydrates, which can be detrimental to health when excessively consumed. Focus should be on wholegrains, beans, vegetables, and legumes, which can help stabilise blood sugar levels compared to refined grains and sugary foods.

Plant-based diets can result in a higher carbohydrate-to-protein ratio, which may pose challenges for individuals genetically predisposed to poor glucose control. Nonetheless, a well-planned plant-based diet can offer greater benefits for blood sugar than a poorly executed animal protein diet.8

In the UK, we frequently fall short of fibre guidelines (30g per day for adults), despite research linking higher fibre intake to improved health outcomes. Both soluble and insoluble fibre are naturally found in plant foods, contributing to the positive health effects associated with these diets.

Plant-based diets are typically rich in soluble fibre, which can help reduce glucose absorption.9 Moreover, fibre from wholegrains has been shown to be particularly beneficial for cardiovascular health, promoting heart function and reducing risk of disease.10 This underscores the importance of prioritising fibre-rich foods in dietary choices.

Individuals who wish to increase fibre intake should do so gradually and ensure adequate water consumption, as sudden increases can lead to digestive discomfort.

Fat

A significant source of dietary saturated fat comes from animal-based foods, which is linked to an increased risk of cardiovascular disease (CVD).11 Consequently, plant-based diets, especially vegan diets, typically have lower saturated fat levels.4 While some meat substitutes and cheese alternatives can be high in saturated fat, they generally contain less than their meat counterparts.12 Nonetheless, it's advisable to consume these in moderation, similarly to high-saturated fat non-plant foods, and prioritise wholefoods such as beans, pulses and tofu over these substitutes.

Plant sources of unsaturated fats include vegetable oils, nuts, seeds, and avocados. However, vegetarian and vegan diets lack fish, particularly oily fish, which are rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Plant foods like flax, chia, and hemp seeds provide alpha-linolenic acid (ALA), but for the body to utilise ALA, it must first be converted into EPA and DHA; however, this conversion process is inefficient, with low conversion rates.

The conversion process can also be hindered by factors like ageing, alcohol, sex (men tend to convert less efficiently than women), genetics, health conditions like diabetes, and nutrient status, particularly low levels of magnesium, zinc, vitamin B6, niacin and vitamin C.13

Directly consuming EPA and DHA is preferable. For those who don't eat fish, marine algae oil supplements are recommended. Algae omega-3 offers a comparable alternative to fish oil, and its production in controlled environments reduces contamination risks from pollutants and heavy metals.

Micronutrients

Plant-based diets can be at higher risk for deficiencies in vitamins and minerals compared to omnivorous diets, which can pose health risks if not properly managed. While they typically contain higher amounts of carotenoids (such as lutein and zeaxanthin), folate, vitamin C, vitamin E, and magnesium, they often have lower levels of retinol, vitamin B12, and zinc.4 Vegans may also particularly lack calcium and iodine, as well as lacking heme iron.

Vitamin B12

Vitamin B12 is primarily found in animal-based foods and some fortified plant-based sources. Vegans are most at risk of vitamin B12 deficiency due to complete exclusion of animal-based foods, whereas variations of a vegetarian diet can receive some vitamin B12 from animal-based foods they include.

Certain population groups following vegan diets require particular attention for B12 supplementation. During pregnancy, vitamin B12 is crucial for foetal development, and deficiencies can increase risk of neural tube defects, similarly to folate. Additionally, B12 deficiency during pregnancy has been linked to higher risk of preterm birth and low-birth-weight infants.14

Iron

Before considering the effects of plant-based diets, it is crucial to recognise that approximately 1 billion people globally are affected by iron deficiency, with around 8% of women in the UK experiencing iron deficiency anaemia.15 Women of childbearing age are particularly vulnerable due to iron loss from menstruation and pregnancy. Those following plant-based diets, especially women, should be mindful of iron intake to reduce deficiency risk.

The primary source of iron in these diets is non-heme iron, which is less bioavailable compared to heme iron found in animal products.16 Numerous plant foods provide non-heme iron, but its bioavailability can be hindered by ANFs such as phytates, tannins, and oxalates. Certain food processing methods, such as cooking, and pairing iron sources with vitamin C can improve absorption rates.17 Calcium can also inhibit iron absorption; therefore if supplementing high doses to rectify a deficiency, take them separately.

A well-planned plant-based diet can meet iron absorption needs.18 However, it can elevate the risk of low iron stores, potentially putting those (especially women) following a plant-based diet at greater risk of iron deficiency if they do not take supplements.

Calcium

Research indicates that following a plant-based diet, particularly veganism, is associated with a greater risk of osteoporosis compared to an omnivorous diet.19 Vegans and ovo-vegetarians must ensure adequate calcium intake through fortified dairy alternatives like plant-based milks and yogurts, which provide calcium comparable to conventional dairy. Non-dairy calcium sources include dark leafy greens, calcium-set tofu, almonds, and sesame seeds. Lacto-vegetarians and lacto-ovo-vegetarians can obtain calcium from dairy.

Foods high in oxalates, such as spinach, can inhibit calcium absorption, limiting bioavailability. A well-rounded dietary approach that includes fortified products and a variety of calcium-rich foods, while considering factors that affect absorption, is vital for those on plant-based diets to maintain healthy bone mineral density and reduce fracture risk. Magnesium, vitamin D3 and vitamin K2 intakes should also be considered.

Iodine

Vegans may be at risk of iodine deficiency unless they include seaweed, fortified foods, iodised salt (although not widely available in the UK), or supplements in their diet.4 However, care must be taken with seaweed consumption as its iodine content can be inconsistent and highly variable, potentially leading to excessive iodine intake.20 Variations of vegetarian diets can receive dietary iodine from dairy products, eggs, and cheese.

Zinc

Many plant foods contain zinc; however, its bioavailability is often restricted by the presence of ANFs.21 High consumption of phytates (found in cereals, legumes, nuts and seeds) can lead to reduced zinc absorption.22 However, food processing techniques such as cooking, soaking and fermenting have been shown to reduce phytate content within phytate-rich foods, increasing mineral availability such as zinc, iron, and calcium.23

Plant-Based Diets and Non-Communicable Diseases

Despite the considerations regarding nutrient deficiencies, macronutrient balance and ANFs, plant-based diets may offer significant health benefits. Research demonstrates that plant-based diets are associated with lower body mass index, waist circumference, low-density lipoprotein (LDL-c), triglycerides, fasting blood glucose, and both systolic and diastolic blood pressure compared to omnivorous diets.24

Adherence to a plant-based diet is also associated with other health benefits, such as lower serum total cholesterol concentrations25 and reduced incidence of type 2 diabetes mellitus (T2DM),26 and obesity.27

These benefits may stem from various nutritional factors, particularly high intakes of plant polyphenols, namely flavonoids, phenolic acids, and lignans, which have been found to be protective against conditions like CVD and T2DM.28 Additionally, the consumption of wholegrains has been associated with a lower risk of developing T2DM, CVD, and weight gain.29 Higher dietary fibre intake through consumption of wholegrains and other plant foods has been associated with improved insulin sensitivity as well as reduced risk of CVD and mortality.30

A Guide to Plant-Based Diets

Nutrient Diet Affected Suggested Daily Dose
Protein Vegan and vegetarian diets. 0.75g per kg of body weight; higher for athletes and older adults. Pea protein is an excellent plant-based source.
EPA/DHA Vegan and vegetarian diets. At least 250mg DHA (for maintenance of normal brain function and vision) and 100–150mg EPA from algae oil.
Vitamin B12 Vegan and vegetarian diets. 100µg as maintenance; 1000µg if deficient (methylcobalamin form).
Iron Vegan and vegetarian diets. 14–20mg as citrate or bisglycinate.
Selenium Vegan diets. 200µg as L-selenomethionine or sodium selenite.
Calcium Vegan diets. 800mg from supplements and/or fortified foods.
Zinc Vegan diets. 15mg as zinc citrate.
Iodine Vegan diets. 150µg as potassium iodide.
L-Lysine Vegetarian and vegan diets. At least 800mg in free form.

Are You Prescribed Any Medications?

Ensure to check for potential contraindications and seek medical approval before taking dietary supplements.

References

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