Tea produced from the tea plant (Camellia sinensis) is potentially beneficial for health: it contains theanine and caffeine which may improve short-term physiological outcomes such as accuracy of attention,(1,2) and polyphenols, specifically flavan-3-ols, which may improve long-term health outcomes such as cardiovascular diseases.(3,4) The aim of this systematic review and meta-analysis was to update the overall understanding of the effects of tea, or theanine (alone or in combination with caffeine), on cognition, mood, and/or sleep outcomes in healthy participants.

The Cochrane Library, Embase, and Medline were systematically searched, up to and including August 2023, for randomised controlled trials investigating the short-term effects of tea, theanine alone, or theanine plus caffeine interventions, on cognition, mood, and sleep outcomes in healthy participants. Where possible, meta-analysis was performed using standardised mean differences (SMD), or mean differences, with 95% confidence intervals (CI), in random effects models. SMDs and CIs were re-expressed (ReSMD) in the units of the most common measurement tool used by the studies in each meta-analysis.

Fifty RCTs were included in the review; data from fifteen RCTs were eligible for at least one meta-analysis. In the first hour (h1) and second hour (h2) after intake, differences were found between the effects of theanine plus caffeine, and placebo, that favoured the former, on cognitive outcomes including choice reaction time (h1; ReSMD: -24.71 ms; 95 % CI: -51.90 to 2.48), digit vigilance task accuracy (h2; ReSMD: 1.59 %; 95 % CI: 0.17 to 3.01), and attention switching task accuracy (h2; ReSMD: 1.10 %; 95 % CI: 0.43 to 1.77), and mood outcomes including overall mood (h2; ReSMD: 3.46 units on the caffeine research visual analogue scale; 95 % CI: -1.36 to 8.28) and alertness(h2; ReSMD: 2.94 units on the Bond-Lader visual analogue scale; 95 % CI: −0.87 to 6.75). Improvements favouring theanine, compared to placebo, were found for cognitive outcomes including rapid visual information processing accuracy (h2; ReSMD: 1.20 %; 95 % CI: 0.75 to 1.65) and reaction time (h2; ReSMD: -9.77 ms; 95 % CI: -16.98 to -2.55), and choice reaction time (h1; ReSMD: -18.01 ms; 95% CI: -31.27 to -4.83). No consistent evidence was found to indicate whether tea or theanine were beneficial for sleep.

This meta-analysis provides evidence that theanine plus caffeine, and theanine alone, possibly improve attention and mood, however, tea-inequivalent doses, small numbers of studies eligible for meta-analysis, and confidence intervals showing uncertainty surrounding the direction and magnitude of overall effect sizes, were common. More research of tea or tea-equivalent bioactive doses, in free-living participants, would be beneficial. PROSPERO registration no. CRD42022351601

Randomised controlled trials are the ‘gold standard’ approach in nutrition research to show a causal relationship between a dietary intervention and clinically relevant outcomes at the population level. Here we review why different study designs are needed to establish the efficacy of dietary interventions at the individual level and to better account for relevant factors that can also influence the outcomes. Over the past decade, precision nutrition approaches have been developed as a new way to measure the effectiveness of dietary interventions at the individual and population level. Precision nutrition aims to determine the individual factors that are associated with differences in responses to dietary interventions. This is complex, typically needing studies with a large number of participants and using advanced statistical approaches and machine-learning algorithms to identify predictors that can explain why individuals do or do not respond to consuming specific foods, meals or diets, for a given outcome. N-of-1 study designs, which are new to nutrition science, offer a robust alternative approach to assess how an intervention and everyday behaviours affect individual health outcomes. They utilise repeated measures within individuals, rather than baseline and end measures in a larger number of participants, to provide the statistical power required to determine an individual’s responsiveness to an intervention. The adoption of new study designs and modelling approaches, particularly the N-of-1 approach, to examine responses to interventions within individuals, will help to further the understanding of the relationships between diet and health within individuals more effectively and accurately.

Dietary patterns (DP) rich in plant foods are associated with improved health and reduced non-communicable disease risk. In October 2021, the Nutrition Society hosted a member-led conference, held online over 2 half days, exploring the latest research findings examining plant-rich DP and health. The aim of the present paper is to summarise the content of the conference and synopses of the individual speaker presentations are included. Topics included epidemiological analysis of plant-rich DP and health outcomes, the effects of dietary interventions which have increased fruit and vegetable (FV) intake on a range of health outcomes, how adherence to plant-rich DP is assessed, the use of biomarkers to assess FV intake and a consideration of how modifying behaviour towards increased FV intake could impact environmental outcomes, planetary health and food systems. In conclusion, although there are still considerable uncertainties which require further research, which were considered as part of the conference and are summarised in this review, adopting a plant-rich DP at a population level could have a considerable impact on diet and health outcomes, as well as planetary health.

Food phytochemicals are increasingly considered to play a key role in the cardiometabolic health effects of plant foods. However, the heterogeneity in responsiveness to their intake frequently observed in clinical trials can hinder the beneficial effects of these compounds in specific subpopulations. A range of factors, including genetic background, gut microbiota, age, sex and health status, could be involved in these interindividual variations; however, the current knowledge is limited and fragmented. The European network, European Cooperation in Science and Technology (COST)-POSITIVe, has analysed, in a systematic way, existing knowledge with the aim to better understand the factors responsible for the interindividual variation in response to the consumption of the major families of plant food bioactives, regarding their bioavailability and bioefficacy. If differences in bioavailability, likely reflecting differences in human subjects’ genetics or in gut microbiota composition and functionality, are believed to underpin much of the interindividual variability, the key molecular determinants or microbial species remain to be identified. The systematic analysis of published studies conducted to assess the interindividual variation in biomarkers of cardiometabolic risk suggested some factors (such as adiposity and health status) as involved in between-subject variation. However, the contribution of these factors is not demonstrated consistently across the different compounds and biological outcomes and would deserve further investigations. The findings of the network clearly highlight that the human subjects’ intervention studies published so far are not adequate to investigate the relevant determinants of the absorption/metabolism and biological responsiveness. They also emphasise the need for a new generation of intervention studies designed to capture this interindividual variation.

Assessment of national dietary guidelines in a number of European countries reveals that some are based on cohort studies, focusing on total seafood consumption, while others are based on the content of EPA and DHA, distinguishing between oily and other fish. The mean actual intake of fish in most countries is around or below the recommended intake, with differences in intake of fish being present between sex and age groups. Many people do not reach the national recommendation for total fish intake. Dietary recommendations for fish and EPA/DHA are based mainly on data collected more than 10 years ago. However, methods of farmed fish production have changed considerably since then. The actual content of EPA and DHA in farmed salmon has nearly halved as the traditional finite marine ingredients fish meal and fish oil in salmon diets have been replaced with sustainable alternatives of terrestrial origin. As farmed salmon is an important source of EPA and DHA in many Western countries, our intake of these fatty acids is likely to have decreased. In addition, levels of vitamin D and Se are also found to have declined in farmed fish in the past decade. Significant changes in the EPA and DHA, vitamin D and Se content of farmed fish means that average intakes of these nutrients in Western populations are probably lower than before. This may have consequences for the health-giving properties of fish as well as future dietary recommendations for fish intake.

The efficacy by which dietary interventions influence risk markers of multi-factorial diseases is mainly determined by taking population-based approaches. However, there exists considerable inter-individual variation in response to dietary interventions, and some interventions may benefit certain individuals or population subgroups more than others. This review evaluates the application of nutrigenomic technologies to further the concept of personalised nutrition, as well as the process to take personalised nutrition to the marketplace. The modulation of an individual's response is influenced by both genetic and environmental factors. Many nutrigenetics studies have attempted to explain variability in responses based on a single or a few genotypes so that a genotype may be used to define personalised dietary advice. It has, however, proven very challenging to define an individual's responsiveness to complex diets based on common genetic variations. In addition, there is a limited understanding of what constitutes an optimal response because we lack key health biomarkers and signatures. In conclusion, advances in nutrigenomics will undoubtedly further the understanding of the complex interplay between genotype, phenotype and environment, which are required to enhance the development of personalised nutrition in the future. At the same time, however, issues relating to consumer acceptance, privacy protection as well as marketing and distribution of personalised products need to be addressed before personalised nutrition can become commercially viable.

Long-chain n-3 PUFA from fish oil protect against death from CHD but mechanisms are not well understood. Preliminary results indicate that fish oil may affect the enzyme soluble epoxide hydrolase (sEH) and influence inflammatory pathways in a time-dependent manner. In the present study male apoE knockout (Apoe− / − ) mice were randomised to three dietary groups receiving a high-fat high-cholesterol diet supplemented with 2 % (w/w) high-oleic acid sunflower-seed (HOSF) oil, DHA oil or fish oil. Livers and proximal aortas were collected on day 2 and on weeks 1, 2, 4 and 10 to determine hepatic sEH levels, hepatic fatty acid composition, hepatic proteome and atherosclerotic plaque size in the aortic root. Intervention with fish oil, but not with DHA, resulted in significantly lower levels of hepatic sEH levels with time compared with HOSF oil. DHA and fish oil caused differential regulation of thirty-five hepatic proteins which were mainly involved in lipoprotein metabolism and oxidative stress. All mice developed atherosclerosis without differences in plaque size between the three groups. Thus EPA may be responsible for lowering levels of hepatic sEH and both fish oil and DHA could beneficially affect lipoprotein metabolism and oxidative stress.

Nutrition research has slowly started to adopt the proteomics techniques to measure changes in the protein complement of a biological system. This enables modelling of biological processes in response to dietary interventions, as well as the elucidation of novel biomarkers for health or disease that are sensitive to such interventions. There are limited studies on the effect of micronutrients on the proteome, so this review concentrates rather more on dietary intervention studies that have used proteomics (mainly classical 2D gel electrophoresis combined with mass spectrometry) to elucidate changes in pathways that relate to glucose and fatty acid metabolism, oxidative stress, anti-oxidant defence mechanisms and redox status. The ability to measure regulation of more low abundant proteins, such as those involved in inflammatory pathways, as well as the evaluation and validation of newly discovered candidate biomarkers in human biofluids, may depend on the introduction of more quantitative and sensitive methods like multiple reaction monitoring (MRM) and multiplexed immunoassays in nutrition research.

Cafestol and kahweol, coffee lipids present in unfiltered coffee brews, potently increase LDL-cholesterol concentration in human subjects. We searched for an animal species in which cafestol similarly increases LDL-cholesterol. Such an animal model could be used subsequently as a model to study the mechanism of action of cafestol and kahweol. Cafestol and kahweol increased serum lipids in African green monkeys (Cercopithecus aethiops), cebus (Cebus apella) and rhesus (Macaca mulatta) monkeys, hamsters, rats and gerbils differently from the increase in human subjects. In African green monkeys, the rise in total cholesterol was less pronounced than that in human subjects. In addition, the increase in total cholesterol was predominantly due to a rise in HDL-cholesterol rather than LDL-cholesterol. Thus, the rise in plasma lipids might illustrate the mechanism in these monkeys rather than the mechanism in human subjects. In other animal species, cafestol and kahweol did not raise cholesterol consistently. The variability in effects on serum lipids could not be explained by the mode of administration or dose of diterpenes, nor by the amount of cholesterol in the diet. In conclusion, we did not find an animal model in which cafestol and kahweol elevate plasma lipoproteins to the same extent as in human subjects. For the time being, therefore, studies on the mechanism of action should be done preferably in human subjects.

Boiled coffee contains the lipid compounds cafestol and kahweol, which raise cholesterol strongly in man. These lipids are retained by paper filters. In a search for an animal model for the effect of coffee lipids on serum cholesterol concentrations, we fed hamsters (Mesocvicetus aurutus) and rats on mash diets consisting of a purified base diet and either boiled water, unfiltered boiled coffee or filtered boiled coffee. After a feeding period of 8 weeks there was no statistically significant effect of unfiltered boiled coffee on serum total cholesterol and triacylglycerol concentrations in either the hamsters or the rats. The level of serum cholesterol did respond predictably to the addition of cholesterol and/or saturated fatty acids to the diet. The lack of effect of unfiltered boiled coffee in the hamsters and the rats, when compared with the previously reported activity in humans, could not be explained by dosage, duration of treatment, mode of administration or by insufficient statistical power. It is concluded that hamsters and rats are insensitive to unfiltered boiled coffee and thus are unsuitable models for investigating its hyper- cholesterolaemic effect.