The global pandemic of obesity in the modern world and its related health complications have inspired consumers to shift to healthier lifestyles and more nutritious food options. This is clearly evident in the exponential demand for dietary supplements and the meteoric rise of both the nutraceutical and health wellness industries. In fact, as of 2023, the global nutraceutical market is a US$317 billion industry and is expected to grow to almost US$600 billion by 2030 based on annual growth rate of 9.4% (1). Superfoods or (functional foods) is another relatively new term to describe foods packed with nutrients. In contrast to nutraceuticals which are packaged in dosage forms, superfoods can be consumed as it is (2). However, as attractive as it is for health-conscious consumers, the scientific basis for the classification of superfoods has been less stellar, with the term itself appearing to be used chiefly for marketing purposes by modern “experts” such as influencers and celebrities (3–5). Major health institutions such as the American Diabetes Association (ADA), American Heart Association (AHA) the US Departments of Agriculture (USDA) and Health and Human Services (USHHS), to name a few, continue to advocate healthy eating “patterns” such as MyPlate, Mediterranean Diet and Dietary Approaches to Stop Hypertension (DASH), all of which revolve on the premise that the totality of what the individuals eat and drink is a much better predictor of health versus individual foods (6–8). Despite underwhelming clinical evidence, there is sustained interest in exploring the benefits of superfoods within scientific communities, although current available literature has been unfortunately focused mainly on exploring nutritional properties and potential clinical benefits of superfoods (9–11).

The majority of superfoods are fruits and vegetables which are universally classified as healthy. Habitual intake of these types of foods containing polyphenols, oligosaccharides and fiber are known to increase gut microbial diversity, a key component of longevity and decreased risk from chronic diseases (12, 13). Among the roster of superfoods include the leafy greens such as kale (Brassica oleracea). Previous, albeit limited clinical studies investigated the nutraceutical potential of kale and reported that the consumption of kale powder for 8 weeks normalized blood pressure, lipids and glucose levels among individuals at high risk for metabolic syndrome (14). Similarly, in healthy Japanese individuals, consumption of kale-containing foods at a dose of 7 g and 14 g significantly decreased postprandial plasma glucose (15). Among men with hypercholesterolemia, a 12-week supplementation with kale juice not only substantially improved serum lipid profiles but also reduced atherogenic index by as much as 24% (16).

In contrast to kale, green peas (Pisum sativum L) is yet to be considered a superfood and more appreciated as a common fast-food type of vegetable in Western diets due to its wide availability, cost effectiveness and use as a food substitute (17). Current evidence however is trying to shift these outdated concepts, with animal studies indicating peas have beneficial effects in glucose tolerance and improving gut microbiota composition (18, 19). A head-to-head comparison between kale and pea in terms of nutritional value based on USDA data shows that while both have high vitamin C, dietary fiber and potassium content, kale is a better source of vitamins A, K and calcium while pea has substantially more fiber, alpha-carotene and thiamine (20).

In the present cross-over trial, the acute metabolic benefits of freeze-dried kale and green pea supplementation were compared among Arab women with obesity. To the best of our knowledge, the study is the first of its kind to investigate whether common and cheaper vegetable staples such as peas can match up to kale, which is one of the most hyped super foods in recent history, in terms of acute metabolic benefits despite differences in nutritional values.

The major findings in the present cross-over trial are that supplementation of both freeze-dried kale and peas resulted in favorable changes in the anthropometric and metabolic parameters overtime among Saudi Arabian women with obesity, and that freeze-dried peas were superior to kale in terms of glycemic control, since only Hba1c and C-peptide did not exhibit significant carryover effects as compared to other parameters assessed including anthropometrics, lipids and markers of gut dysfunction. It is worthy to note that randomization yielded mostly non-significant baseline differences and the cross-over design further eliminated between-subject variability, adding merit to the advantage of peas over kale as a possible adjuvant management for people at risk of T2DM. We previously examined the acute effects of kale and pea supplementation without the cross-over (initial phase) and similarly found favorable effects in both groups with respect to reduction in abdominal obesity, with a marginal difference in favor of kale in terms of weight loss (23). All in all, the results suggest that while there is evidence to support that superfood kale supplementation yields beneficial outcomes, these outcomes were comparable, if not inferior, to less-hyped vegetable such as green peas.

Recent studies utilizing pea supplementation have focused on muscle strength and as substitute for whey protein (27, 28), as well as improvement in glycemic status and gut microbiota composition in one animal simulation study (glucose-intolerant mice) using pea seed coats (18). The favorable alteration in the glycemic and gut microbiota composition can be explained by the decreased FABP2 observed in the pea group overtime, a finding that was opposite in the kale group, which showed increased FABP2 levels prior to crossing over to pea. FABP2, which is exclusively produced in the small intestine, is a marker of gut permeability and a marker of diabetes-related complications such as nephropathy (29). Nevertheless, in the present study, both the pea and kale groups had increased FABP2 in the first 2 weeks, with only the kale group showing a significant change. This increase maybe a reflection of pre-existing endothelial dysfunction, since the obesity-mediated chronic inflammatory state affects endothelial dysfunction through mechanisms independent from the production of inflammatory adipocytokines and elevated free fatty acids by adipose tissue (30). After the washout period and the initiation of a longer 4-week supplementation, we observed that FABP2 decreased in both groups (significant in crossover kale) and this could be due to reduced food intake secondary to modestly improved measures of central obesity. To the best of our knowledge, the present study is arguably the first to examine the effects of pea supplementation on glycemic and gut composition parameters using a crossover design.

Both kale and peas contain high amounts of dietary fiber, vitamin C, carotenoids, bioactive compounds, and trace elements in varying amounts (23), all of which can significantly influence the gut microbiota in terms of microbial diversity and endothelial integrity as a whole. Kale in particular contains bile sequestrants which regulates bile acid recirculation subsequently reducing fat absorption and improving lipid metabolism (31). Since both kale and pea supplementation modestly improved the lipid profile of participants, better glycemic status was anticipated. Although the glycemic parameters (C-peptide, HOMA-IR and HOMAβ) assessed in the present study showed no significant change post-supplementation, it is well established that a high lipid environment induces peripheral insulin resistance and production of reactive oxygen species (ROS) (32), therefore regulating lipid parameters can indirectly modify glycemic status. Other markers assessed in the present study such as CD14, showed no changes in participants given pea first and increased among those given kale first. CD14 as a surrogate measure of gut permeability is said to be elevated among individuals with obesity and those who adhere to a Western-based diet (33). The elevated levels of CD14 seen among participants given kale first should be interpreted with caution, given that more established markers of gut permeability and dysbiosis such as endotoxin showed no substantial changes in both groups over time in the present study. This elevation maybe a direct consequence of the dietary intake of participants during the intervention period and not from the supplementation itself.

Another interesting finding is that while weight loss was observed only in the kale group, both groups had decreased WHR post-supplementation. The apparent weight loss confirms a previous survey done in Arab adults which revealed that 51.1 and 20.2% of those who had earlier used kale reported weight loss and decreased in appetite, respectively, (34). Both kale and pea contain substantial amounts of dietary fiber which is known to induce weight loss by increasing satiety (35, 36), although worthy to note is that peas actually have a relatively higher fiber content (5.7 g/100 g) than kale (4.1 g/200 g) (23). Increased fruit and vegetable consumption in general alter body adiposity composition as observed in large-scale studies (37, 38). Nevertheless, and due to the short-term duration of the study, the acute weight loss observed can also be reduction only in water weight since decreased caloric intake, specifically in carbohydrates, decrease water retention (39). Furthermore, the regulation of adipogenesis may explain the improvement in central obesity by some phytochemicals present in kale. Through aryl hydrocarbon receptors (AhR), a kale-rich diet alters the stability of genes and proteins involved in adipogenesis, such as peroxisome proliferator-activated receptor gamma (PPAR-γ). This AhR–PPAR interaction has recently gained interest as a potential therapeutic target for metabolic diseases (31). Cumulatively, the promotion of kale and pea supplementation in Saudi Arabia may have substantial benefits for its population as this ethnic group in particular appears to be susceptible to obesity and T2DM due to widespread consumption of Western diet of simple sugars, saturated fat, and calorie-dense fast foods (40). While kale already has the advantage of being tagged as the “superfood,” it is worthy to emphasize that peas are also a constant staple of individuals living in “Blue Zones,” which are select places in the world where people live the longest (41), reinforcing that such foods may increase longevity via enhancement of the gut endothelial barrier, a key mechanism that reduces endotoxin which is inversely associated with telomere length, a marker of aging (42).

In the present investigation, while significant carryover effects were observed in most parameters, the interventions being compared are functional foods and not drugs, and as such the cumulative effects of the intervention among participants were positive. This meant that in a clinical sense, the acute consumption of both functional foods of interest (kale and pea), whether taken in intervals or in combination, synergistically translated to substantially lower adiposity levels which can then lead to a better metabolic profile. The observations elicited in the present investigation supports the “healthy dietary pattern,” defined as consuming combination/alternating diets that prevent chronic diseases: high in fruits, vegetables, whole grains, non-fat dairy and lean protein (43). Furthermore, and from an economic standpoint, the present findings provide health-conscious individuals more affordable options (e.g., peas) which are equally, if not more nutritious, minus the “superfood” label. Given the diverse backgrounds (e.g., socioeconomic, medical history, lifestyle) of the participants outside the inclusion criteria, it is safe to assume that the findings can be generalized and applied to wider populations and other ethnic groups, especially among individuals at higher risk for obesity and obesity-related complications. Lastly, the use of freeze-dried kale and pea supplements instead of raw produce merits highlight, as it is well known that freeze-drying not only prolongs the shelf-life of fruits and vegetables, but it also drastically slows down enzymatic, chemical and microbiological reactions, ensuring that the nutrients remain intact and ensuring that the effects observed will most likely be the same if raw produce was consumed (44).

The authors acknowledge several limitations. The significant carryover effects were an unexpected finding but nevertheless indicate that the washout period was not sufficient and therefore several important parameters such as anthropometrics can only be interpreted on the first round of supplementation. Given the cross-over design and the lack of similar studies on the supplements investigated, it was difficult to estimate how long the washout period should be, and extending for longer periods also puts the trial at risk for higher dropout rates (44). Furthermore, the improvements observed in HbA1c should be interpreted with caution given that the trial was short (2–4 week) relative to the time it takes to achieve steady state HbA1c (12–16 weeks). Additional clinical trials using a parallel design and longer follow-up are encouraged are recommended, taking into consideration the limitations of a cross-over trial on understudied supplements (45).

In summary, while both short-term freeze-dried kale and pea supplementation translated to improved metabolic profile among Saudi adults with obesity, the use of pea was superior to kale in terms of glycemic control, suggesting that less promoted, cheaper and more readily available vegetables such as the humble green pea are equally, if not more potent, than media-promoted superfoods such as kale. Longer intervention studies using pea supplementation as an adjuvant therapy for diabetes may yield more interesting results to confirm present findings. Meanwhile, the promotion of healthy dietary patterns in Saudi Arabia should include locally grown, cheaper and more sustainable vegetables such as green peas for consumption among individuals with obesity and those at high risk of diabetes instead of kale and other more expensive, imported and heavily promoted superfood vegetables.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

The studies involving humans were approved by the study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of the College of Medicine, King Saud University, Riyadh, Kingdom of Saudi Arabia (Approval# 21/0049/IRB, 24/12/2020). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

DA: Funding acquisition, Writing – review & editing. SS: Supervision, Writing – original draft. AA: Investigation, Writing – review & editing. AA-F: Investigation, Methodology, Writing – review & editing. TB: Investigation, Methodology, Writing – review & editing. KW: Investigation, Methodology, Writing – review & editing. SH: Formal analysis, Methodology, Writing – review & editing. MA: Investigation, Validation, Writing – review & editing. PM: Conceptualization, Supervision, Writing – review & editing. NA-D: Supervision, Writing – review & editing.