Review of the plant-based nutrition and lifestyle medicine news May 2025

This month I highlight an update to the pillars of lifestyle medicine, along with studies and reports on meat, weight loss, iron, hypothyroidism, misinformation and more.

An update to the pillars of lifestyle medicine

This month the American College of Lifestyle Medicine (ACLM) updated two of its six foundational pillars, stress management and social connection, to reflect evolving scientific understanding and clinical practice. These revisions emphasise a more holistic approach to health, integrating psychological, social, and spiritual dimensions.

The "stress management" pillar now acknowledges the interplay between objective stressors and subjective perceptions, recognising that individual factors such as temperament, personality, and past experiences influence stress responses. The updated framework highlights the importance of addressing both external stressors and internal perceptions through interventions like positive psychology, psychotherapy, and resilience-building strategies. It also considers the cumulative effects of chronic stressors, including discrimination and socioeconomic challenges, which can lead to allostatic load (cumulative burden of chronic stress and life events) and health deterioration.

The "social connection" pillar has been renamed "connectedness" to encompass a broader spectrum of meaningful relationships, extending beyond interpersonal connections to include bonds with nature, companion animals, and spiritual or transcendent elements. This expanded perspective recognises that both horizontal (social) and vertical (spiritual) relationships contribute to an individual's sense of purpose and meaning, which are crucial drivers of health behaviour change and overall well-being. Connectedness is further described in this review article.

These updates underscore the ACLM's commitment to a comprehensive, evidence-based approach to lifestyle medicine, integrating mental, emotional, and spiritual health into the prevention and treatment of chronic diseases.

Meat consumption, health outcomes and industry influence

Red meat consumption continues to be a significant focus of public health research due to its association with chronic diseases such as type 2 diabetes, cardiovascular disease, and certain forms of cancer. An analysis of over 200,000 participants across three major U.S. cohorts, followed for 28 years, found that higher intakes of both processed and unprocessed red meat were consistently linked to an increased risk of type 2 diabetes, even among those following an otherwise high-quality diet (as assessed using the Alternative Healthy Eating Index). The higher risk persisted even after adjusting for BMI, waist circumference, and weight change, suggesting the harms of red meat are independent of body weight. The study also demonstrated that substituting red meat with healthier foods, such as plant-based proteins, whole grains, or seafood, was associated with lower diabetes risk. The benefit of lowering red meat consumption was greater in participants with a higher diet quality.

This study helps to counter the narrative that the negative health impacts of red meat consumption are due to the fact that consumption is associated with an overall unhealthy diet. In fact, there was a greater risk associated with red meat in those who ate a healthier diet. In addition, it has been suggested that it is the food that red meat is consumed with that is responsible for harm. But this study also addressed this and showed that even in people with the lowest french fries consumption there was still a greater risk of developing type 2 diabetes. Substitution analysis showed that replacing red meat for refined grains was also beneficial, so we can’t even blame the bun!

Processed meats, in particular, raise significant concerns given their classification as carcinogenic by the World Health Organization. Rates of cancer, particularly in people under the age of 50 years continues to rise, with diet and lifestyle factors most certainly implicated. A new report from the Food Foundations called Meat Facts finds that in the UK, nearly one-third of meat consumed is processed, with especially high intakes seen among children and younger men. The UK is consuming twice as much meat as the global average and 42% of meat consumed is chicken, despite the concerns around antibiotic resistance, pandemic risk, use of soya feed from areas of deforestation. Sadly, chicken consumption is likely to only increase especially with KFC investing 1.5 billion into the UK. There is an urgent need for public health messaging and government policies to support the reduction of meat consumption whilst increasing consumption of healthy plant-based foods.

The scientific literature on red meat is further complicated by issues of industry influence. A 2025 systematic review revealed that studies with financial ties to the red meat industry were far more likely to report neutral or favourable health outcomes related to unprocessed red meat consumption. In contrast, all studies without industry ties reported either neutral or unfavorable outcomes. This pattern mirrors what has been observed in other areas of public health research, including studies on tobacco and sugar-sweetened beverages, raising serious concerns about the role of industry sponsorship in shaping scientific narratives.

Importantly, the health effects of reducing red meat depend significantly on what replaces it in the diet. Research has shown that substituting red meat with refined carbohydrates or other animal proteins such as white meat or fish may not lead to significant health improvements, and in some cases may even be detrimental. This is a study design ‘trick’ used by industry players to minimise the effect size of any potential harm attributed to red meat consumption. However, replacing red meat with high-quality plant-based foods like legumes, nuts, and whole grains consistently yields better outcomes for cardiovascular and metabolic health. This highlights the importance of specificity in dietary recommendations, general advice to reduce red meat intake is insufficient without guidance on appropriate substitutions.

Despite mounting evidence, UK dietary guidelines offer only broad recommendations to reduce red and processed meat with relatively high upper limit of 70g per day of red meat.. In contrast, international frameworks, such as the EAT-Lancet Planetary Health Diet, advocate for more precise limits, recommending no more than 14 grams of red meat per day for both health and environmental sustainability. The Planetary Health Diet was first and foremost based on health and secondarily found to also be sustainable for planetary health. Public education, policy interventions, and industry accountability are needed to bring consumption in line with current scientific understanding. It’s worth noting that men in general consume more meat than women as shown in the Meat Facts report and corroborated by this new study from France. These habits are formed early in life according to this study from Sweden, in which diets of 4-years olds failed to meet sustainability goals with boys more likely to be consuming higher quantities of environmentally damaging foods such as meat.

The AHDB (Agriculture and Horticulture Development Board), a farmer levy board supported by Defra, continues to try and persuade us that red meat is a necessary component of a ‘healthy, balanced diet’. Their new report ‘Balancing health and sustainability: the role of red meat in the UK diet’ is counter to all the available evidence. The seventh carbon budget from the UK’s Climate Change Committee make it clear that the UK needs to reduce the number of farmed cows and sheep and significantly reduce the consumption of red meat and dairy to meet climate and nature goals. The target set is to reduce red meat consumption by 40% by 2050. There is no role for red meat consumption in a sustainable future.

A key argument remains the fact that red meat is a source of readily bioavailable iron and diets low or absent in red meat will increase the risk of iron deficiency. Interestingly, new research challenges this assumption. A controlled trial titled Dietary Adaptation of Non-Heme Iron Absorption in Vegans found that long-term adherence to a vegan diet is associated with physiological adaptations that enhance non-haem iron absorption. The study, which compared iron absorption between omnivores and vegans, demonstrated that despite the absence of haem iron in the vegan diet, overall iron status remained within normal ranges. Vegans exhibited increased fractional absorption of plant-based (non-haem) iron, suggesting that the human body may up-regulate absorption mechanisms in response to lower dietary iron bioavailability. These findings call into question the prevailing narrative that red meat is indispensable for maintaining adequate iron status and support the feasibility of plant-based diets in meeting nutritional needs when appropriately planned. Of course longer more in depth studies are required, but available evidence does not find an increased risk of iron deficiency anaemia in people following meat-free diets.

Weight loss medications and the need for complementary nutrition and lifestyle approaches

The recent surge in the use of GLP-1 receptor agonists (GLP-1RAs) like semaglutide and tirzepatide for obesity treatment has raised important concerns about nutritional adequacy. People on these medications report a marked reduction in appetite and thus risk nutritional deficiency if diet quality is not addressed at the same time.

A cross-sectional study published in Frontiers in Nutrition examined dietary intake in GLP-1RA users and found that many individuals using these medications do not meet the recommended dietary intake (DRI) for essential nutrients. Across a sample of adults using GLP-1RAs for at least one month, researchers found consistent shortfalls in intake of fiber, calcium, iron, magnesium, potassium, choline, and key vitamins including A, C, D, and E. Participants also had lower-than-recommended protein intake when calculated per kilogram of body weight, which is especially concerning given that rapid weight loss on GLP-1RAs can lead to significant loss of lean body mass. The study concluded that tailored nutrition interventions are urgently needed for this population to support adequate intake, maintain muscle mass, and prevent long-term nutritional deficiencies.

Complementing this, a joint advisory from leading organisations, including the American College of Lifestyle Medicine and the American Society for Nutrition, underscores that GLP-1 therapies are most effective when combined with comprehensive nutrition and lifestyle support. This includes ensuring sufficient intake of protein (1.2–2.0 g/kg/day during weight loss), calcium, iron, magnesium, zinc, and vitamins A, D, E, K, B1, B12, and C. Without structured dietary guidance, individuals may experience not only micronutrient deficiencies but also functional impairments such as muscle wasting and bone loss. The advisory also recommends that clinicians integrate registered dietitian / nutritionists and health coaches into care teams to provide personalised support before, during, and after weight loss therapy. Structured physical activity, particularly strength training and consistent movement, is also considered as an essential part of any care plan for patients using GLP-1 medications, to preserve lean mass, support metabolic health, and improve long-term outcomes. Additional challenges include prevention of weight regain after stopping weight loss medications. New research shows that most people have regained the lost weight within a one year period.

These findings point to the need for a shift in how GLP-1-based weight management is delivered. Historically, medical nutrition therapy and lifestyle medicine approaches have not kept pace with pharmacologic advances, similar to early gaps in support for bariatric surgery patients. Now, the evidence clearly calls for the development of specialised nutritional guidelines, food-as-medicine programs and lifestyle medicine support for those using GLP-1RAs. Doing so not only mitigates risks of malnutrition and lean mass loss but may also help patients sustain weight loss and improve long-term health outcomes.

New studies addressing common misconceptions about plant-based diets

Plant-based diets are often criticised for being high in ultra-processed foods, which of course is not a problem unique to this diet pattern. So it is useful to see this secondary analysis of a randomised trial, including 244 overweight adults assigned to either a vegan diet group or a control group for 16 weeks. The vegan group avoided all animal products and minimised oils but was not restricted in energy intake or the inclusion of processed foods. Dietary intake was analysed using the NOVA classification system, which categorises foods from unprocessed (category 1) to ultra-processed (category 4).

At the end of the study, the vegan group experienced an average weight loss of 5.9 kg compared to the control group, a statistically significant result. Crucially, weight loss was strongly associated with reduction in animal product intake across all NOVA categories, including unprocessed, processed, and ultra-processed forms. In contrast, there was no significant association between consumption of processed plant-based foods and weight gain.

Multivariate regression analysis confirmed that the top three predictors of weight loss were reduced intake of unprocessed or minimally processed animal foods, processed animal foods and ultra-processed animal foods

Even when adjusting for total energy intake and other confounders, reductions in these categories remained significantly predictive of weight loss. Importantly, participants in the vegan group consumed a variety of plant-based foods across all processing levels, yet still lost weight, suggesting that the origin of the food (animal vs. plant) is a more critical determinant of weight outcomes than the level of processing alone.

The authors conclude that replacing animal products with low-fat plant-based foods, even if some are processed, can be an effective strategy for weight loss. This challenges common criticisms that vegan diets are inherently unhealthy due to their potential inclusion of ultra-processed foods. While the study does not suggest that all processed foods are nutritionally optimal, it highlights that processed plant-based foods do not negate the benefits of a plant-based diet when replacing higher-fat, calorie-dense animal products.

Additionally, plant-based diets are also criticised for being high in carbohydrates, with carbohydrates being blamed for obesity and type 2 diabetes. Of course not all carbohydrate-rich foods are created equal. This large prospective cohort study followed over 90,000 women from the Nurses’ Health Study for more than 30 years and analysed their dietary patterns in relation to a comprehensive index of healthy ageing. “Healthy ageing” in this study was defined as survival to at least age 70 without major chronic diseases (such as cancer, diabetes, or cardiovascular disease), cognitive impairment, or physical disabilities. Carbohydrate intake was assessed in midlife and ranged from 37-57% of total energy.

The analysis showed that both higher total intake and higher-quality intake of carbohydrates were associated with healthier ageing. Diets rich in high-quality carbohydrates, such as whole grains, fruits, vegetables, and legumes, were positively associated with healthy ageing. The benefits seen were greater in those consuming the most fibre. Conversely, diets with a higher glycaemic index or higher intake of refined carbohydrates, added sugars and starchy vegetables were associated with worse outcomes. In substitution analyses, high-quality carbohydrate intake was associated with higher odds of healthy ageing when replacing energy from refined carbohydrates, total fat, animal protein, and trans fatty acids, but not when compared with energy from total or plant protein, saturated or polyunsaturated fatty acids. So there is absolutely no need to fear carbohydrates when consumed in minimally processed plant-based foods, including fruit.

Finally, there is still doubt around adherence and quality of a plant-based diet. This new study “Scoring Adherence to Voluntary Restriction Diets (SAVoReD) in the ADAPT Study” developed and validated a scoring tool to measure how closely individuals follow self-selected dietary patterns, including vegan, whole food plant-based (WFPB), vegetarian and paleo diets. Using data from over 2000 adults, the study applied the SAVoReD index to assess diet quality, consistency, and the degree to which people adhered to the core principles of their chosen diet, based on self-reported food frequency questionnaires.

The WFPB diet was defined not just by the absence of animal products, but by a focus on unrefined plant foods, vegetables, fruits, legumes, whole grains, nuts, and seeds, with minimal intake of added oils, sugars, and processed foods. In contrast, the vegan diet excluded animal products but allowed for a broader range of processed foods, including many ultra-processed vegan products.

Sixty-one percent of participants reported that they have been following their chosen diet for >2 years and 46% reported following for >5 years. The mean adherence score for all diets was 71.3% (range 25-100 %). Vegans had the highest mean adherence score (75.2%), followed by vegetarians (74.6%), WFPB (70.2%), with Paleo diet followers found to have the lowest adherence score (64.9%). Adherence to a vegan or WFPB diet was associated with a lower BMI compared to the other diet groups, with longer duration (>2 years) of following the diet associated with a lower BMI. A WFPB diet was associated with higher diet quality as defined by the healthy eating index (HEI) whereas the Paleo diet had the lowest quality due to higher intakes of saturated fat and lower intakes of fruit, plant protein and whole grains.

The authors conclude ‘greater adherence to more plant-based diets may support nutritional health…….healthier BMI and with diet quality. While, our results suggest that individuals may benefit from being encouraged to follow these diets with greater adherence, our results also indicate even imperfect or flexible adherence to these diets may be associated with improved levels of health indicators like HEI and BMI’.

Do meat-free diets increase the risk of hypothyroidism?

An interesting new study suggests that there may be a higher risk of hypothyroidism in people eating a meat-free diets. The study included 466,362 participants from the UK Biobank, of which 220,514 followed a high meat, 221,554 a low meat, 5242 a poultry-based, 10,598 a pescatarian, 8057 a vegetarian, and 397 a vegan diet. During a median follow-up of 12.7, 10,831 participants developed hypothyroidism. Only after adjusting for BMI, researchers found an increased risk of hypothyroidism in low-meat, poultry-based, pescatarian and vegetarian participants compared to high meat eaters, with the strongest association for vegetarian participants. The vegan group was too small for meaningful results.

The researchers discuss whether BMI in this setting is a ‘collider’ rather than ‘confounder’. A collider is a variable that is influenced by both the exposure (in this case, diet) and the outcome (hypothyroidism). Adjusting for a collider in statistical models can introduce spurious associations or mask true ones, leading to biased estimates. This is a well-known concept in epidemiology and causal inference. In this study, diet affects BMI: Vegetarians and vegans typically have lower BMI than meat-eaters. BMI is associated with hypothyroidism: Higher BMI is linked to higher risk of hypothyroidism. Therefore, BMI is a collider on the path between diet and hypothyroidism.

Interestingly, data from the Adventist Health Study 2 also found that vegetarians, but not vegans, had an increased risk of hypothyroidism after adjusting for BMI. In this study, higher BMI was associated with increased incidence and prevalence of hypothyroidism.

The most plausible mechanism is that people eating vegetarian and vegan diets have a lower intake of iodine as demonstrated by the results of the current study. In the presence of low iodine intakes, higher intakes of cruciferous vegetables, may also affect thyroid hormone synthesis. Interestingly, vegetarians who consume dairy, which is a major source of iodine, still had lower intakes compared to meat and fish eaters. Vegetarian and vegans in this cohort also had lower intakes of zinc, selenium and vitamin B12 that could be in part responsible for the higher risk of hypothyroidism.

Whilst we have two studies to date on the topic of plant-based diets and hypothyroidism, further research is needed to establish if there is a true increase in risk for people on meat free diets and whether this is fully explained by lower intakes of certain micronutrients. We also need to understand if a fully plant-based/vegan diet also carries a similar risk to a vegetarian diet. In the meantime, the advice to people on a meat free diet remains the same. Make sure you plan appropriately at all stage and ages of life to obtain sufficient amounts of essential nutrients. In the UK, where salt is not routinely iodised, it is advisable to take an iodine supplement.

Are vegan diets worse for glucose regulation than vegetarian diets that include dairy?

A randomised study of 30 participants in India compared the impact of a vegan versus lacto-ovo vegetarian diet on glucose regulation over a 14 day period. Both diets provided approximately 2,000 kcal/day and were matched for energy, macronutrients, fibre, and added sugar. To replicate typical Indian dietary preferences, dairy milk was substituted for chocolate soya milk, since tea is usually drunk with added sugar. A subset of participants underwent testing for various plasma metabolites that reflecting metabolic pathways relevant to diet.

While the study reports statistically significant elevations in mean glucose levels in individuals consuming a vegan diet compared to a lacto-vegetarian diet, the clinical significance of these findings is limited. The reported mean glucose concentration in the vegan group, 85.5mg/dL or 4.75 mmol/L remained well within the normoglycemic range and only modestly exceeded the lacto-vegetarian value, 78.5mg/dL or 4.36mmol/L. This small difference, approximately 7 mg/dL or 0.39mmol/l, does not meet thresholds for concern in healthy individuals, especially over a short, 14-day intervention. Similarly, other glycemic parameters such as the Glucose Management Indicator (5.4% vs. 5.2%) and time-in-range (70–140 mg/dL), which was in fact higher in the vegan group (79.7% vs. 66.9%), do not suggest impaired glucose regulation.

It is critical to distinguish statistical significance from clinical relevance. In a cohort of young, healthy adults, marginal elevations in mean glucose without evidence of glucose dysregulation or reduced time-in-range should not be interpreted as evidence of metabolic harm.

Concerns might be raised about the observed decrease in acetylcarnitine (C2), a key short-chain acylcarnitine involved in mitochondrial fatty acid oxidation. However, this is best understood as a reflection of dietary intake (low carnitine and saturated fat) and a shift in energy substrate use, rather than mitochondrial dysfunction. There is no evidence that this would have a detrimental effect on health outcomes, especially, when healthy vegan diets have been associated with lower rates of type 2 diabetes and used to induce diabetes remission.

In summary, the short-term vegan dietary intervention produced a modest, clinically insignificant increase in mean glucose, alongside a suite of metabolomic changes of indeterminant significance. It’s worth noting the authors conflict of interests include funding from the dairy industry. Also, if one truly wanted to test the impact of a fully plant-based diet without dairy and optimised for health, chocolate soya milk is not the ideal substitute!

See you all in a month!