1. Introduction
Obesity (OB) is characterized by an excessive accumulation of body fat resulting from an imbalance between daily energy intake and energy expenditure leading to excessive weight. This condition is a multifactorial disease influenced by some of genetic, cultural, and social factors. Contributing factors encompass reduced physical activity, insomnia, endocrine disorders, medication, and an imbalance in macronutrients consumption such as polyunsaturated fatty acids (PUFAs) omega-6 (n-6) and omega-3 (n-3). OB is associated with numerous comorbid and chronic medical conditions including an elevated risk of diabetes
mellitus type 2, cardiovascular disease, hypertension, and dyslipidemia [
1].
Currently, a low PUFAs intake, accompanied by an imbalance in their n-6:n-3 ratio has been described [
2]. In Mexico, a 12:1 n-6:n-3 ratio has been reported, whereas the recommended adequacy suggests a consumption ratio no more than 5:1 [
3,
4]. This imbalance is strongly related with overweight comorbidities, and may contribute to the chronic low-grade inflammation [
2,
5].
In the other hand, the inflammatory response functions as a defense mechanism in the innate immune system to protect the host against detrimental stimuli, however, its activity must be resolved once the threat diminishes. This self-limiting process is crucial for preserving homeostasis [
6]. Nevertheless, the failure to achieve resolution or continued exposure to environmental and biological factors that induce inflammatory response activation, can rise a chronic inflammatory process. This results in the extended presence of immune cells such as lymphocytes, macrophages, and plasma cells in the adipose tissue, accompanied by the secretion of proinflammatory cytokines [
7,
8].
Prolonged existence of chronic low-grade inflammation triggers the infiltration of immune cells and the secretion of inflammatory cytokines within the tissue environment, potentially inhibiting glucose absorption and altering lipid metabolism [
9]. In recent years, attention has been focused on the investigation of the biological resolution of inflammation initiated by specific biochemical signals generated through the ingestion of n-3 PUFA. These potent bioactive molecules are collectively known as specialized pro-resolving mediators (SPMs) that include resolvins (Rv), protectins (PD), and maresins (MaR) [
10]. There are few studies analyzing the anti-inflammatory effects of n-3 PUFAs in subjects with obesity.
Therefore, the aim of this study was to evaluate the effect of a nutritional intervention with 5:1 (n-6:n-3) PUFAs ratio with supplemented n-3 on anthropometric, biochemical, and pro-resolution inflammation parameters in adults with obesity.
4. Discussion
It has been shown that supplementation with n-3 PUFAs have an important role in the treatment of obesity, as they have a favorable impact on chronic low-grade inflammation. However, controversial results persist among different populations, particularly regarding the duration and consumption quantity [
23]. The aim of this study was to assess the effect of a nutritional intervention with average ratio of 5:1 (n-6:n-3) supplemented with n-3, on anthropometric, biochemical, and pro-resolution of inflammation parameters in adults with obesity [
19].
Given the crucial role of patients adherence in this kind of interventional projects, WHO's recommendations for chronic diseases treatments, suggests to achieve at least 50% [
24], which agree with findings in this study due to 60% of adherence was found in both groups, however, more motivational strategies should be use in further studies with satisfaction surveys that leads to improving treatment.
Regarding baseline analysis of three dietary records, all subjects showed an inadequate consumption of n-6:n-3 PUFAs ratio which agree with other studies in Mexican population with obesity [
3,
25,
26] showing an imbalance associated with higher adipose tissue percentage, WC, and higher levels of triglycerides, glucose, and insulin [
3]. Additionally, it contributes to chronic low-grade inflammation in obesity by activating inflammatory pathways and interfering with the synthesis of lipid mediators in pro-resolution inflammation, such as resolvins [
10].
In this study, both groups significantly increased n-3 intake and achieved a dietary n-6:n-3 consumption ratio of <5:1 at the end of the intervention. However, it is noteworthy that the omega-3 group exhibited statistically lower n-6 dietary intake compared to the placebo group. These findings could be related with better metabolic profile and pro-resolution inflammation mediators exposed above.
Analysis of anthropometric variables showed intragroup improvements in weight, body fat percentage, BMI, and waist circumference; however, when comparing these variables between groups, no statistically significant differences were found. We hypothesize that these results could be attributed to the implementation of the same dietary recommendations in the recipes book provided.
Nevertheless, prevalence of abdominal obesity significantly decreased 35% in omega-3 group compared to 5.6% in placebo group. These findings are consistent with meta-analyses that found a relationship between n-3 intake of animal source with better anthropometric measures [
27,
28]. However, the impact of these PUFAs on body composition has been controversial with WC reported as the anthropometric variable related to obesity that has the most significant impact after n-3 supplementation [
28].
Among the biochemical variables, some lipid profile components had an improvement, such as triglycerides and VLDL-c. This could be explained by a mechanism in which n-3 PUFAs act as ligands for peroxisome proliferator-activated receptor alpha (PPAR-α), a transcription factor that promotes the expression of genes involved in β-oxidation of fatty acids [
29,
30], decreasing VLDL-c levels. The VLDL-c is responsible for endogenous transport of triglycerides from the liver to peripheral tissues, including visceral, mainly in the abdominal region [
31]. On the other hand, no effects were observed on HDL-c and total cholesterol, consistent findings with a meta-analysis by Harrys et al., where triglycerides and VLDL-c significantly decreased while HDL-c and total cholesterol were not altered after 7 to 10 weeks of n-3 PUFA supplementation [
32]. Nevertheless, other factors may be involved, such as physical activity and genetic factors related to HDL-c concentrations [
33].
Regarding fasting insulin, it was observed improvements, independently of groups, following the intervention, which may be attributable to the same dietary regimen and the favorable impact of an adequate diet on insulin levels [
34]. Furthermore, the HOMA index consistently displayed improved parameters in the omega-3 group throughout the intervention, indicating a beneficial effect. The correlation between omega-3 fatty acids and the free fatty acid receptor 4 (FFAR4) elucidates the potential mechanisms underlying the observed effects on glucose metabolism and insulin levels. Activation of FFAR4 by omega-3 fatty acids has been associated with enhancements in insulin sensitivity and glucose homeostasis [
35,
36]. Nevertheless, literature reports inconclusive n-3 effects on these variables in humans [
37] might be due glucose homeostasis is influenced by other factors beyond n-3 intake, such as lifestyle, physical activity, body fat percentage, among others [
34,
37,
38]. Given this complexity, further clinical trials with longer time, are necessary, as our intervention lasted only 8 weeks and that the activation of FFAR4 can be evaluated.
Other metabolic consequences of obesity associated with the imbalance of n-6:n-3 PUFA ratio intake, is the maintenance of chronic low-grade inflammation affecting pro-resolution inflammation processes mainly in adipose tissue [
39,
40]. Studies in vitro and clinical trials, have demonstrated that n-3 PUFAs, particularly EPA and DHA, decrease the number of resident macrophages in adipose tissue and crown-like structures characteristic of the M1 phenotype. In addition to the decrease in levels of MCP-1, a chemotactic protein with a key role in the initiation, development, and perpetuation of chronic low-grade inflammation in obesity [
41,
42], consistent with the findings of this study, where MCP-1 levels were lower in the omega-3 group both intragroup and compared between groups at the end of the intervention.
Similarly, IL-6 concentrations were lower in the omega 3 group both intra and intergroups at the end of the intervention, consistent with the study of Milutinivic et al., who evaluated the effect of n-3 supplementation (2.4 g/day) for 8 weeks on inflammatory markers, highlighting a statistically significant decrease of IL-6 [
43]. Moreover, a meta-analysis published in 2021 by Wei Y. et al., including 31 studies between 2003 and 2019, aimed to study the effect of inflammatory markers and the n-6:n-3 PUFA ratio consumption in various inflammatory etiology diseases, emphasizing obesity and associated comorbidities. Omega-3 supplementation has been associated with the modulation of inflammation through the nuclear factor κB (NF-κB) pathway. Research indicates that omega-3 fatty acids can influence markers of inflammation by inhibiting the production of pro-inflammatory cytokines and regulating the NF-κB signaling pathway [
44]. As in this study, they concluded that systemic levels of IL-6 and TNF-α were lower in subjects with lower n-6:n-3 consumption ratio as has been documented in the literature [
45].
Regarding RvD1, which belongs to the family of lipid pro-resolution inflammation mediators, increased significantly compared to baseline in omega-3 group along with IL-10. This supports the hypothesis proposed in this study, as RvD1 is synthesized from DHA metabolism [
10,
46,
47], and the omega-3 group had a higher total consumption compared to placebo group. Additionally, it has been reported that RvD1 promotes the synthesis of IL-10 [
48] which agrees with a study by Polus et al., included 59 women with obesity provided with dietary guidelines and supplementation with 1.8 g/day of n-3 for 12 weeks. In proportion, they observed 58% of increase in RvD1 plasma levels, and an in-crease in IL-10, compared to baseline in n-3 supplemented group. Although our results are consistent, the higher increased in Polus et al. study may be due to the longer intervention (12 vs. 8 weeks) [
22]. This finding suggests that the chronicity of n-3 consumption favors the incorporation of these PUFAs into the cellular membranes phospholipids [
4], and as a result, the enhancement of the RvD1 synthesis involved in inflammation resolution processes by reducing the activation of the NF-κB-mediated cascade, leading to reported decreases of TNF-α, IL-6, MCP-1, and increase IL-10 [
46,
49,
50].
Perspectives of this study, are to increase the intervention time including more sub-jects, analyze more inflammatory and pro-resolution molecules with others methodologies such as chromatographic, to allow us to corroborate data and elucidate cellular mechanisms where n-6:n-3 PUFA ratio is involved.
Moreover it is necessary that health professionals and governmental programs, pro-mote an adequate consumption of n-6:n-3 PUFA ratio intake due to their association with obesity and related disorders where a chronic low-grade inflammation is present.
Author Contributions
All authors contributed significantly to this article. J. T-V: conceptualization, data curation, investigation, methodology, development of experiments, writing—original draft and editing. R. R-E: development of experiments, investigation, super-visions. W. C-P: methodology, formal analysis, resources, supervision, writing–original draft, writing–review and editing. C. R-R: methodology, development of experiments. S.R-P: collected the data, data curation, M.P-R: writing–original draft, writing–review and editing, E.M-L: conceptualization, data curation, formal analysis, funding acquisition, methodology, project administration, resources, supervision, visualization, writing–original draft, writing–review and editing. All authors have read and agreed to the published version of the manuscript.