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The impact of egg consumption on indices of gastrointestinal health: a systematic literature review
- N. Sultan, E. Cheng, N. Kellow, C. Tuck, J. Biesiekierski
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- Journal:
- Proceedings of the Nutrition Society / Volume 83 / Issue OCE1 / April 2024
- Published online by Cambridge University Press:
- 07 May 2024, E71
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- Article
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Eggs are highly digestible, nutrient-rich and are a valuable source of protein and choline, thereby promoting a range of health benefits. Several studies have found an association between protein intake and gastrointestinal microbial diversity(1), while bacterial fermentation of undigested protein in the large bowel can produce short-chain fatty acids, such as butyrate, positively influencing host metabolic health, gut integrity and immune function(2). On the other hand, dietary choline stimulates gastrointestinal bacterial production of trimethylamine and the prothrombotic compound trimethylamine-N-oxide (TMAO)(3). Despite these established links, limited studies have explored the effects of whole egg intake on indices of gastrointestinal health. This systematic literature review aimed to synthesise research that has investigated the impact of egg-supplemented diets or egg consumption on markers of gastrointestinal health including microbiome, function and symptoms. This review was conducted in accordance with PRISMA guidelines. Five databases (Ovid Medline, Embase, CINAHL Plus, SCOPUS, and PsychInfo), and reference lists of relevant papers, were searched from inception until April 2023. Studies were included if they examined the link between whole chicken egg consumption and gastrointestinal health in healthy adults (aged>16). Indices of gastrointestinal health were defined as any outcomes related to gastrointestinal factors, including symptoms, microbiome, inflammation, colonic fermentation and TMAO. Reviews and case studies were excluded. All studies underwent risk of bias assessment. Overall, 548 studies were identified and 19 studies were included after screening. Eight of these were randomised controlled trials (RCTs), 8 cross-sectional and 3 prospective cohort studies. Participants ranged in number between 20-32,166 and in age between 18–84 years. Study periods varied between 3–14 weeks for RCTs and 6 months–12.5 years for prospective cohort studies. RCTs examined intakes between 1–4 eggs/day, with the majority examining 3 eggs/day (n = 6). The primary outcome across 15 articles was TMAO levels, with most reporting no significant associations (n = 13). Five studies examined inflammation with inconsistent findings ranging from no alterations (in TNF-α, IL-8, CRP), increases (in anti-inflammatory marker LTB5, TNF-α), and decreases (in IL-6, CRP). Lastly, 7 studies explored alterations in microbiome. Two RCTs and 2 cross-sectional trials reported no alterations in microbial diversity in response to eggs. Meanwhile, 2 cross-sectional and 1 prospective study linked specific bacteria to consistent egg intake. Eggs were associated with species that produce butyrate (E.rectale, F.prausnitzii, M.smithii, and R.bromii), and protect against metabolic syndrome (A.muciniphila). This systematic review found that egg consumption did not increase levels of the undesirable biomarker TMAO and were associated with butyrate-producing bacteria. Evidence regarding the effect of egg intake on inflammation was inconsistent. This review revealed the general lack of available research investigating whole eggs and gastrointestinal health. Future carefully designed RCTs are required to improve understanding of how eggs may influence the gastrointestinal microbiome and colonic fermentation.
The impact of egg consumption on cognitive function: a systematic literature review
- N. Sultan, E. Cheng, C. McMahon, N. Kellow, C. Tuck, J. Biesiekierski
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- Journal:
- Proceedings of the Nutrition Society / Volume 83 / Issue OCE1 / April 2024
- Published online by Cambridge University Press:
- 07 May 2024, E181
-
- Article
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- You have access Access
- Export citation
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Eggs provide several nutrients that have been linked to neurological function. Phospholipids, which comprise 30% of lipids in egg yolk, modulate neurotransmitter receptors and have been shown to lower reaction time in healthy adults(1). Eggs are also high in choline (340mg per egg), a building block for acetylcholine, a neurotransmitter involved in memory, learning and attention(2). Finally, eggs contain the omega-3 fatty acid docosahexaenoic acid (DHA) (25mg per egg), which has roles in neurological function including neurogenesis, synaptic plasticity and myelination(3). The impact of whole egg consumption on cognition has not been widely explored. This systematic review aimed to consolidate studies that investigated frequency of egg consumption or egg-supplemented diets on cognitive function. This review followed PRISMA guidelines and involved a search of five databases (Ovid Medline, Embase, CINAHL Plus, SCOPUS, and PsychInfo) from inception until April 2023. Included studies examined the link between whole chicken egg consumption and brain function, including cognitive decline, memory, risk-taking, reaction-time, decision-making, and executive function, in healthy adults (aged>16 y). All studies underwent risk of bias assessment. Twelve studies were included in the review. Four were prospective cohort studies, 4 were retrospective, 3 cross-sectional and 1 was a randomised controlled trial (RCT). Participant numbers, with the exception of the RCT, ranged between 178-9028 and were aged between 42-97 years. Duration of prospective studies varied from 2-5 years. Egg intake was measured via food frequency questionnaires (n = 8), 24-hr diet recalls (n = 2), a 4-day food record (n = 1) and a 7-day food record (n = 1). The RCT provided 2 DHA-fortified eggs/day compared to 2 whole eggs/day for 8 weeks. The primary outcome across 9 studies was cognitive decline, followed by memory (n = 7), reaction-time (n = 2), attention (n = 2), and executive function (n = 1). For outcome measures, studies used 9 different validated task-oriented tools (including the Montreal Cognitive Assessment n = 3, and California Verbal Learning Test n = 2), or 4 self-completed questionnaires. Several studies found no significant associations between egg consumption and cognitive decline (n = 4) or memory (n = 2). Conversely, 5 studies reported significant inverse associations between egg consumption and rates of cognitive decline. The RCT found that reaction-times were faster on both whole eggs and DHA-eggs after 8 weeks (p>0.05 between groups). Although conflicting results were found, more studies showed a greater frequency of habitual egg consumption to be associated with reduced cognitive decline. However, the variety of outcome measures across studies make direct comparisons challenging, preventing definitive conclusions about the impact of eggs on cognitive health. This review highlights the need for future RCTs.