Vegetarian Diets and Their Effect on n-3 Polyunsaturated Fatty Acids Status in Humans: Systematic Review

Vegetarian diets limit the consumption of foods of animal origin to a variable extent, potentially leading to deficiencies in specific nutrients, particularly proteins and n-3 polyunsaturated fatty acids (n-3 PUFA) from fish or seafood. This systematic review aimed to assess the impact of vegetarian diets on n-6 and n-3 PUFA status in humans, with a focus on critical periods such as pregnancy and growth. Studies were included if they evaluated the relationship between vegetarian diets and PUFA status with clearly defined vegetarian diet types and PUFA measurement methods. Exclusion criteria included systematic reviews, meta-analyses, and studies that included occasional meat or fish consumption. A comprehensive literature search was conducted in PubMed, Springer, and ScienceDirect databases, considering articles published up to 2023. A total of 45 studies were involved; the review found that vegetarian diets increased linoleic acid (C18:2 n-6, LA) and alpha-linolenic acid (C18:3 n-3, ALA) intake but resulted in significantly reduced concentrations of eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n-3, DHA), particularly in vegan diets. DHA intake from microalgae oil was shown to effectively improve serum DHA status, particularly during pregnancy and lactation. The evidence included in this review is limited by variations in study designs, potential biases in dietary reporting, and inconsistencies in PUFA (especially intake) measurement methods. These findings highlight the need for strict dietary planning and supplementation strategies to mitigate deficiencies, particularly during critical developmental periods.