How sustainable are hypocaloric and balanced diets for weight loss?

This study aimed to evaluate the level of alignment to a sustainable pattern of historical diets prescribed in an urban nutritional care facility specialized in weight loss according to national guidelines [14]. The objective was to identify the actual state of the art and possible issues to facilitate the transition towards sustainable diets. In addition, we evaluated how patient characteristics affected alignment of prescribed diets to EAT-IT and analyzed historical diets prescribed in an urban nutritional care facility specialized in weight loss according to national guidelines [14].

Our findings revealed significant sex-based disparities in dietary adherence. Diets prescribed to men exhibited lower adherence compared to those prescribed to women. This discrepancy can likely be attributed to the higher protein requirements of men from their greater body weight and higher proportion of lean muscle mass [20, 21]. To meet these needs, men tend to consume more animal-based proteins, leading to a lower intake of prescribed legumes. However, it’s also important to consider that cultural perceptions regarding protein sources may contribute to this trend [22,23,24]. In Western societies, animal protein is often perceived as a superior or more desirable source of protein compared to vegetable protein [25,26,27]. This perception could influence food choices, leading to a preference for meat and a reduced consumption of pulses, even when plant-based options are readily available and nutritionally adequate [28,29,30,31].

Furthermore, we observed a slight inverse relationship between BMI and adherence to certain food groups. This suggests that reducing calorie intake for weight loss becomes increasingly challenging as obesity severity increases. This is especially evident in lower adherence to vegetable oils and higher adherence to whole grains. These data highlight the decreased sustainability of weight loss diets in individuals with higher BMI due to the increased metabolic demands associated with more severe obesity [20, 32,33,34].

A significant portion of the prescribed food groups did not align with the recommendations of the EAT-Lancet reference diet. This discrepancy underscores the inherent challenges in developing dietary interventions that are both sustainable and effective for weight loss [21, 35]. The specific types of foods that showed the greatest non-adherence, particularly protein sources, emphasize the critical role of protein intake in hypocaloric diets [20, 34]. While adequate protein is crucial, excessive protein intake, especially from animal sources, can pose several challenges [2, 5, 7, 32]. As highlighted by the EAT-Lancet guidelines [5], which advocate for a more moderate protein intake, excessive consumption of animal-based proteins can pose potential health concerns, such as the stimulation of cell proliferation as suggested by Willett et al. [5], to the significant environmental burden associated with animal agriculture, including substantial demands on land, water, and overall resource utilization, as well as increased pollution [5].

These findings highlight the complex interplay between nutritional needs, dietary sustainability, and the challenges of achieving optimal dietary adherence in the context of weight management. In short-term hypocaloric diets, protein source and quality, particularly animal proteins, can differentially impact weight loss [25]. Animal proteins, being high-quality and well-digested, effectively stimulate muscle protein synthesis, potentially leading to greater weight loss and lean mass preservation, especially when combined with resistance exercise and associated with positive metabolic outcomes and reduced mortality risk in specific populations [27, 36, 37]. However, long-term, normocaloric diets emphasizing plant-based foods are linked to slower weight gain compared to those high in animal proteins [25]. Furthermore, plant-based proteins offer benefits in reducing chronic disease risk due to fiber, vitamins, minerals, and phytochemicals [38]. However, adopting healthier, sustainable protein choices faces practical challenges: established taste preferences for animal proteins, limited culinary skills for preparing tasty plant-based alternatives, ingrained cultural and social norms around traditional protein sources, and the potential issues of accessibility and affordability of diverse plant-based options [38].

The aim of increasing micronutrients intake while consuming less food resulted in low adherence of fruits and high adherence of vegetables. This is because fruit has more calories, albeit limited ones, due to its higher sugar content than vegetables. However, ensuring adequate intake of micronutrients in hypocaloric diets is essential for supporting metabolic health, preventing nutrient deficiencies, and promoting successful and sustainable weight loss in individuals with obesity [39]. To meet micronutrient requirements, both those recommended for the general population and any increased requirements due to obesity-related comorbidities (e.g. anemia, bone loss), it is not uncommon to supplement the diet with vitamin and mineral supplements and mineral waters, particularly those rich in calcium. Moreover, weight loss maintainers, relative to individuals with lower weight loss and stable obesity, have higher odds of meeting recommendations for several micronutrients, reporting higher Healthy Eating Index-2015 scores, which suggests a greater intake of fruits, vegetables, beans, and whole grains in the long-term [32]. Indeed, some micronutrients, such as fibres and B-vitamins, contribute to feelings of fullness and satiety. Including micronutrient-rich foods in hypocaloric diets can help control hunger and reduce the risk of overeating. Moreover, vitamins and minerals deficiencies during weight loss can lead to various health issues, such as weakened immune system, hormonal dysfunctions, an increase in bone loss, fatigue, and impaired cognitive function, in addition to impaired resting energy metabolism, potentially hindering weight loss efforts [32, 39].

This study has its limitations. Although the sample size is substantial, comprising approximately 4000 diets, we only possess details of the prescribed diets, without knowledge of actual food intake, as would be obtained through a structured food consumption investigation, such as a 7-day food diary. Despite this, the study has the potential to guide professionals, including those in clinical practice, towards evaluating the environmental impact of dietary treatments for diseases, particularly obesity, which is steadily increasing in prevalence. It is worth noting that this study compared and calculated the sustainability score of the prescribed diets using the EAT-IT, the Italian adapted model, rather than the original EAT-Lancet. This decision was made due to the lack of detailed information in the EAT-Lancet, particularly in some food subcategories, regarding both frequency and portions (e.g. canned fish, snacks and dried fruits, prescribed for their ease of use). Furthermore, our analysis focused on the influence of BMI and gender; however, it’s important to acknowledge that patient characteristics are multifaceted and extend beyond these two factors. Other potentially influential variables, such as pre-existing comorbidities, physical activity levels, occupational demands, educational attainment, socioeconomic status, and dietary habits, were not included in this study. This exclusion limits the comprehensiveness of our assessment and the ability to fully account for the heterogeneity within our patient population. Future research could explore the impact of these additional factors on adherence to sustainable dietary patterns.

All these results combined show how hypocaloric diets for weight loss currently prescribed struggle to meet the sustainability requirements described in the EAT-IT diet. As highlighted by Tucci et al. [9], when prescribing hypocaloric diets, it is crucial to ensure nutritional adequacy in hypocaloric diets, carefully monitoring and adjusting macronutrient and micronutrient intake to prevent deficiencies and ensure overall health. This is particularly important in long-term weight management, as inadequate nutrient intake can hinder weight loss efforts and negatively affect metabolic health. It is important to acknowledge that the EAT-IT model is a flexible framework rather than a rigid dietary prescription [6,7,8,9]. While it provides a valuable reference point, it can be adapted to individual needs and preferences. For example, the absence of specific food categories like canned fish in the EAT-IT model does not necessarily exclude their use. However, it is crucial to consider the environmental impact and nutritional value of such choices, and to incorporate them into the diet in appropriate quantities and frequencies. Aligning prescribed diets with the EAT-IT or EAT-Lancet models could offer several potential benefits:

Improved Health Outcomes: Adherence to a plant-based diet, as advocated by the EAT-IT model, has been associated with reduced risk of chronic diseases such as heart disease, type 2 diabetes, and certain cancers.
Environmental Sustainability: A diet rich in plant-based foods and low in animal products has a significantly lower environmental footprint, contributing to a more sustainable food system.
Weight Maintenance: A sustainable weight loss approach, as promoted by the EAT-IT model, can lead to better long-term weight management and a reduced risk of weight regain, similarly to vegan and vegetarian diets. Furthermore, this approach can enhance long-term adherence by accommodating lower meat consumption and respecting cultural and local dietary traditions [2, 3, 40].

In conclusion, this study emphasizes that balanced diets for weight loss do not meet environmental sustainability criteria yet, and we still need to make an effort in this direction. Healthcare professionals play a pivotal role in promoting sustainable and effective weight loss interventions. By understanding the environmental impact of dietary choices and aligning them with patient needs, we can contribute to both individual and planetary health. Future research should explore innovative approaches to develop evidence-based guidelines and tools to support clinicians in this endeavor, ultimately leading to more sustainable and effective weight loss strategies. To bridge this gap and improve the sustainability of future dietary prescriptions, it will need to be proposed the following:

Develop a standardized assessment tool: This tool would assess patients’ dietary habits, considering both nutritional needs and environmental impact.
Integrate sustainability education: it will enhance training programs to emphasize the environmental implications of dietary choices and equip the teams with the knowledge and tools to incorporate sustainability principles into dietary counseling.
Collaborate with stakeholders: collaborate with dietitians, nutritionists, and environmental experts to develop and implement practical strategies for promoting sustainable diets in our clinical setting.
Conduct regular reviews and updates: review practices and update framework based on the latest evidence and best practices in sustainable nutrition.

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