Most societies witness an ever increasing prevalence of both obesity and dementia, a scenario related to often underestimated individual and public health burden. Overnutrition and weight gain have been linked with abnormal functionality of homoeostasis brain networks and changes in higher cognitive functions such as reward evaluation, executive functions and learning and memory. In parallel, evidence has accumulated that modifiable factors such as obesity and diet impact the gut–brain axis and modulate brain health and cognition through various pathways. Using neuroimaging data from epidemiological studies and randomised clinical trials, we aim to shed light on the underlying mechanisms and to determine both determinants and consequences of obesity and diet at the level of human brain structure and function. We analysed multimodal 3T MRI of about 2600 randomly selected adults (47 % female, 18–80 years of age, BMI 18–47 kg/m2) of the LIFE-Adult study, a deeply phenotyped population-based cohort. In addition, brain MRI data of controlled intervention studies on weight loss and healthy diets acquired in lean, overweight and obese participants may help to understand the role of the gut–brain axis in food craving and cognitive ageing. We find that higher BMI and visceral fat accumulation correlate with accelerated brain age, microstructure of the hypothalamus, lower thickness and connectivity in default mode- and reward-related areas, as well as with subtle grey matter atrophy and white matter lesion load in non-demented individuals. Mediation analyses indicated that higher visceral fat affects brain tissue through systemic low-grade inflammation, and that obesity-related regional changes translate into cognitive disadvantages. Considering longitudinal studies, some, but not all data indicate beneficial effects of weight loss and healthy diets such as plant-based nutrients and dietary patterns on brain ageing and cognition. Confounding effects of concurrent changes in other lifestyle factors or false positives might help to explain these findings. Therefore a more holistic intervention approach, along with open science tools such as data and code sharing, in-depth pre-registration and pooling of data could help to overcome these limitations. In addition, as higher BMI relates to increased head micro-movements during MRI, and as head motion in turn systematically induces image artefacts, future studies need to rigorously control for head motion during MRI to enable valid neuroimaging results. In sum, our results support the view that overweight and obesity are intertwined with markers of brain health in the general population, and that weight loss and plant-based diets may help to promote brain plasticity. Meta-analyses and longitudinal cohort studies are underway to further differentiate causation from correlation in obesity- and nutrition-brain research.

Older adults (≥65 years) are the fastest growing population group. Thus, ensuring nutritional well-being of the ‘over-65s’ to optimise health is critically important. Older adults represent a diverse population – some are fit and healthy, others are frail and many live with chronic conditions. Up to 78% of older Irish adults living independently are overweight or obese. The present paper describes how these issues were accommodated into the development of food-based dietary guidelines for older adults living independently in Ireland. Food-based dietary guidelines previously established for the general adult population served as the basis for developing more specific recommendations appropriate for older adults. Published international reports were used to update nutrient intake goals for older adults, and available Irish data on dietary intakes and nutritional status biomarkers were explored from a population-based study (the National Adult Nutrition Survey; NANS) and two longitudinal cohorts: the Trinity-Ulster and Department of Agriculture (TUDA) and the Irish Longitudinal Study on Ageing (TILDA) studies. Nutrients of public health concern were identified for further examination. While most nutrient intake goals were similar to those for the general adult population, other aspects were identified where nutritional concerns of ageing require more specific food-based dietary guidelines. These include, a more protein-dense diet using high-quality protein foods to preserve muscle mass; weight maintenance in overweight or obese older adults with no health issues and, where weight-loss is required, that lean tissue is preserved; the promotion of fortified foods, particularly as a bioavailable source of B vitamins and the need for vitamin D supplementation.

In recent years, a wealth of factors are associated with increased risk of developing non-alcoholic fatty liver disease (NAFLD) and NAFLD is now thought to increase the risk of multiple extra-hepatic diseases. The aim of this review is first to focus on the role of ageing and sex as key, poorly understood risk factors in the development and progression of NAFLD. Secondly, we aim to discuss the roles of white adipose tissue (WAT) and intestinal dysfunction, as producers of extra-hepatic factors known to further contribute to the pathogenesis of NAFLD. Finally, we aim to summarise the role of NAFLD as a multi-system disease affecting other organ systems beyond the liver. Both increased age and male sex increase the risk of NAFLD and this may be partly driven by alterations in the distribution and function of WAT. Similarly, changes in gut microbiota composition and intestinal function with ageing and chronic overnutrition are likely to contribute to the development of NAFLD both directly (i.e. by affecting hepatic function) and indirectly via exacerbating WAT dysfunction. Consequently, the presence of NAFLD significantly increases the risk of various extra-hepatic diseases including CVD, type 2 diabetes mellitus, chronic kidney disease and certain extra-hepatic cancers. Thus changes in WAT and intestinal function with ageing and chronic overnutrition contribute to the development of NAFLD – a multi-system disease that subsequently contributes to the development of other chronic cardiometabolic diseases.

A plant-based diet, which can include small amounts of meat, is the foundation for healthy sustainable diets, which will have co-benefits for health, climate and the environment. Studies show that some of the barriers to making this dietary change and reducing meat consumption are perceptions that plant-based diets are inconvenient, it takes too much time and skills to prepare meals and ingredients are expensive. The food environment is changing and the industry is responding with the exponential increase in the market of highly processed, convenient and cheap plant-based foods. This overcomes some of the barriers, but there is concern about whether they are healthy and environmentally sustainable. Plant-based foods have a halo effect around health and the environment, but many being produced are ultra-processed foods that are high in energy, fat, sugar and salt and have a higher environmental impact than minimally processed plant-based foods. The trend towards eating more highly processed plant-based convenience foods is a concern with regard to both public health and the targets set to reduce greenhouse gas (GHG) emissions. The ‘modern day’ plant-based diet emerging is very different to a more traditional one comprising pulses, vegetables and wholegrain. Studies show that those who are younger and have been a vegetarian for a shorter duration are eating significantly more ultra-processed plant-based foods. While there is a place for convenient, desirable and affordable plant-based food to encourage dietary change, care should be taken that this does not subconsciously set a path which may ultimately be neither healthy nor sustainable.

Plant-based (PB) diets are associated with good health and are also recommended for environmental sustainability. The present review aimed to summarise the definitions of PB diets globally and to investigate the nutritional role of PB diets in adults. This review found that there is a wide range of PB definitions ranging from the traditional vegetarian diets (including vegan) to semi-vegetarian/flexitarian diets. Furthermore, other diets which were originally developed due to their associations with positive health outcomes, such as the portfolio, Mediterranean-style, DASH, healthy US-style, planetary health and Nordic-style diets, have been encompassed in PB definitions due to their emphasis on certain PB components. This review has highlighted that those consuming a PB diet are more likely to meet recommended intakes for carbohydrate, dietary fibre and vitamin E and are less likely to meet recommendations for protein, vitamin B12 and iodine compared to omnivores. Regardless of consumer type, neither PB consumers nor omnivores met recommendations for intakes of vitamin D, calcium and sodium. While intakes of protein, n-3, iron and zinc were generally sufficient from the PB diet, it is important to acknowledge the lower bioavailability of these nutrients from PB foods compared to animal-derived products. As dietary patterns shift towards a more PB diet, there is a need for further studies to investigate the role of PB diets for nutritional adequacy and status in populations currently accustomed to consuming a primarily omnivorous diet.

The aim of this review is to summarise the common barriers and motivations for healthy food choice among adolescents, with a specific focus on the Irish context where available. It will also discuss other concerns adolescents have, which may influence their food choices and eating habits. Adolescence represents a period of rapid physical, mental and social development, and many health-related habits developed during adolescence tend to persist into adulthood, making the teenage years an optimal time to encourage healthy eating and health-promoting behaviours. Adolescents are concerned about the health impact of their diet, but their understanding of health is often seen in the context of their physical appearance or body image. Body image concerns are prevalent in adolescents, and this can affect their food choices. Taste, price and convenience are commonly noted factors influencing adolescents' food choices, and as they grow, their level of independence increases and spending more time with their peers means that social desirability and social norms about food become increasingly important factors in adolescent food choice. However, their limited autonomy means their supporting food environment also plays an important role. When developing more targeted interventions in adolescent populations, information on adolescent nutrition needs, their concerns for health and body image, and the barriers and motivations for healthy eating and food choice should be considered. Such a holistic approach should help support healthy eating and the prevention of overweight and obesity in the population, whilst also supporting a healthy relationship with food and their bodies.

Obesity is a major burden on the health system in England and the rest of the UK. Obesity prevalence is high in adults and children and most of the UK population are consuming more energy than required, and not meeting other dietary recommendations, including those for saturated fat, free sugars, fibre, oily fish and fruit and vegetables. Over the past 5 years, a number of cross-government policies, both promoting voluntary action and legislative, have been put in place to tackle diet-related health and obesity. The food environment is complex with many influencing factors, some of which act through individual automatic choices. Other factors such as accessibility, advertising, promotion and nudging drive increased food and drink purchases. With continual changes in the food environment favouring fast-food outlets and meal delivery companies alongside the adverse impact of the COVID-19 pandemic on diets and physical activity levels, further governmental action is likely needed to deliver sustained improvements to diet and health.