Plant-based and omnivores diets have similar nutrient profiles

The promotion of plant-based diets (PBD) as a means to improve both human and planetary health has gained considerable momentum. However, questions have arisen concerning the nutritional adequacy of PBD, particularly with regard to micronutrients traditionally associated with meat and animal products, such as vitamin B12 and iron. Additionally, the availability of highly processed plant-based foods with unfavourable nutritional profiles also raises concerns.

Assessing the validity of these concerns is further complicated by the substantial diversity in the definition and classification of PBD in research.

Aim

The aim of this review was to assess the diverse definitions of PBD globally and examine their nutritional significance in adult dietary patterns.(1)

Method

The review pooled information from a variety of sources including peer reviewed journals, position statements and vegan and vegetarian society websites.

To evaluate the nutritional impact of PBD, the reviewers identified and analysed eight large observational studies (n=1,475 to 93,823) and three intervention studies (n= 31 to 291). The studies compared PBD with omnivorous diets and included population groups from Belgium, Denmark, France, Sweden, the UK, and the US.

Table 1. Dietary patterns classified as plant-based diets in the literature. All PBD encouraged the consumption of fruits, vegetables, grains, nuts, seeds, beans and pulses.

Nutrition role of PBD

Macronutrients

Energy intakes varied across studies, with some indicating lower energy intake from PBD compared to omnivorous diets, while others found comparable energy intakes among different dietary patterns.

Similar trends were observed for total and saturated fat, as well as protein, with PBD providing either lower or similar levels as omnivorous diets. Notably, the authors highlighted two specific observational studies showing a higher prevalence of inadequate protein intake in vegans (8% to 27%) compared with omnivores (1% to 4%). However, it's worth emphasising that the overall evidence suggests that both PBD and omnivore groups generally meet recommended dietary protein intakes, regardless of variations in intake levels.

Few studies provided information on free sugars. Total sugars intake from PBD was reported to be similar or higher compared to meat-eaters. These findings are difficult to interpret, as a higher total sugars intake in PBD could reflect increased consumption of fruits and vegetables.

In terms of fibre intake, PBD generally exhibited higher intakes (20g to 56g) compared with omnivorous diets (17g to 27g).

Of note are salt intakes which were found to exceed the maximum recommended levels in both plant-based and omnivorous diets.

Micronutrients

Some micronutrients intakes varied depending on the specific composition of the various PBD.

Vitamin A intakes tended to be higher in PBD compared to omnivorous diets, while vitamin D intakes were lower in PBD (0-4mcg vs 2-5mcg). However, it's worth noting that vitamin D intakes can be influenced by different country-specific practices related to dairy fortification. This practice is common in the US but not in the UK and is infrequent in most European countries. Additionally, even in omnivorous diets, vitamin D sources are limited, with reliance on sunlight during certain times of the year and use of supplements for vulnerable population groups.(2)

Vitamins and minerals within recommended intakes for both PBD and omnivorous diets

Vitamins E, C, thiamine, folate, potassium, and magnesium intakes from PBD were either similar or greater than omnivorous diets, with both dietary patterns meeting recommended intake targets.

PBD intakes of riboflavin, niacin, vitamin B6, and selenium were lower or comparable to those of omnivorous diets, and again, both dietary patterns met nutritional recommended intake levels.

Variance between PBD types

Vitamin B12 intakes tended to be lower in vegan diets, particularly without the use of supplementation, whereas PBD that incorporated some meat and/or dairy were more likely to have intakes comparable to those in omnivorous diets.

Similarly, calcium intakes in PBD that included dairy (vegetarian, pescatarian, semi-vegetarian, and Mediterranean diets) provided more calcium compared with vegan diets, which also had significantly lower levels than omnivorous diets. Most studies indicated sufficient calcium intake in PBD, but the extensive EPIC-Oxford study showed calcium inadequacies in both meat eaters and vegans. It's worth noting that calcium fortification is now standard in non-organic plant-based dairy alternatives, a practice not prevalent during the time frame of many studies included in this review.(2)

Iron intakes from PBD (13-23mg) were either higher or similar to that in omnivorous diets (9-17mg). Primary plant-based iron sources included green leafy vegetables, beans, lentils, as well as nuts and seeds. Despite the lower bioavailability associated with plant-based foods, a recent meta-analysis, cited by the authors, demonstrated that although vegan populations had lower ferritin stores, there was no difference in the prevalence of iron deficiency anaemia between vegans and omnivores.(2)

Zinc intake data give a more complex picture. Generally, studies in this review displayed considerable variance, with some indicating lower intakes in PBD and others showing comparable intakes to omnivorous diets. Furthermore, some studies found intakes from PBD to be within recommended levels, while others indicated a higher prevalence of insufficient intakes in vegans compared to meat eaters.

Iodine intake was notably affected by the inclusion of fish, milk, or iodine-fortified plant-based beverages in the diet. Overall, while all omnivorous diets adhered to US recommendations for iodine intake, the majority of vegans and approximately one-third of vegetarians had inadequate intakes. It's interesting to note that the fortification of plant-based drinks and dairy alternatives with iodine began only in recent years, and this would not have been reflected in the studies selected for this review.(2)

Conclusion

In summary, dietary patterns classified as PBD vary significantly in their composition – some including all or some animal products, whilst others moderate their intake and encourage significantly high consumptions of specific plant foods. Despite these variations, when comparing PBD to omnivorous diets, most macro and micronutrient levels are comparable and generally align with dietary recommendations. This includes protein, iron, and most vitamins. However, vitamin B12, calcium, and iodine levels tend to be lower in vegan diets in comparison to other PBD types that include some animal products. Zinc intake findings across different diets are conflicting.

Iron intakes, on the other hand, tend to be higher in PBD, and despite concerns about lower bioavailability, the evidence indicates no difference in the prevalence of iron deficiency anaemia between vegans and meat eaters.

A concerning commonality across all dietary patterns is insufficient calcium intakes and excessive salt consumption exceeding recommendations.

While the authors emphasise reduced bioavailability of certain nutrients like protein, n-3, iron, and zinc, it's essential to note that this is based on short-term and single meal studies and does not reflect more recent evidence of adaptation to diets higher in anti-nutrients over the long-term. Additionally, clinical evidence demonstrates no greater protein malnutrition in Western population groups consuming a vegan diet compared to omnivorous..

Further research is necessary to confirm the impact of long-term dietary adaptations on nutrient provision and to differentiate outcomes between healthful and unhealthful dietary plant-based patterns.

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