The present study verified that the diet had a positive impact on the quality of life, and lipid profile of systemic lupus erythematosus patients. Three randomized controlled trials (RCTs) were included; however, due to the heterogeneity of the studies in relation to the control group and the moment of evaluation, it was not possible to perform the data meta-analysis. Nonetheless, to verify the effect size of interventions and compare it among the groups, the data presentation of choice was by effect size estimation.
According to Shah et al. , the diet intervention presented a small effect on the quality of life improvement. The questionnaire used by the authors assessed the general energy level, ability to perform specific tasks, quality of sleep, satisfaction with food eaten, satisfaction with personal life, relationships, etc. According to Chaigne et al. , musculoskeletal involvement, socio-demographic factors, fatigue, and comorbidities are directly related to the quality of life of systemic lupus erythematosus patients and can be modified when subjected to a controlled diet.
The European League Against Rheumatism (EULAR) stated that the quality of life-related to health is an important parameter and should be continuously evaluated in the clinical routine. Regarding the quality of life, the authors did not attribute a slight improvement to the diet itself, but the intensity of counselling received by patients in the intervention group.
The disease activity assessed by Systemic Lupus Erythematosus Disease Activity Index 2 K > 4 at the end of the study conducted by Silva et al. , which lasted for six months, did not show any relevant difference between the group submitted to the diet and the control group. According to the authors, the groups did not differ regarding the corticoid dose used throughout the study. The authors observed that there was a significant change in the intervention group, with a reduction in the carbohydrate, saturated fat, trans and total fat, and calories intake. There was no change in the body mass index among participants in the intervention group, but when compared to the control group, these participants presented a weight gain. As the adipose tissue secretes pro-inflammatory cytokines, the increased adipose mass may contribute to the inflammation worsening, which may justify the disease activity worsening in the control group .
The subject is still controversial, but there is a suggestion that obesity and a high-fat diet are related to SLE, with the frequency of obesity being higher in SLE patients than in the general population. Vitamin D deficiency and increased adipokines, such as leptin and adiponectin, may explain the relationship between obesity and SLE .
Regarding the lipid profile, the study conducted by Shah et al.  showed that the diet improved the high-density lipoprotein, low-density lipoprotein, and triglyceride levels at both 6 and 12 weeks, which was more accentuated at 12 weeks. Silva et al.  showed an improvement in high-density lipoprotein, low-density lipoprotein, and triglyceride levels in adolescents at the 9-month evaluation. The results of both studies prove the effectiveness of protecting the cardiovascular system through diet and that adults and adolescents adhered to the proposed diet. For involving adolescents, the study conducted by Silva et al.  proves that the diet can be effective even among groups that are usually resistant to changing habits . According to the Update of the Brazilian Guideline on Dyslipidemias and Prevention of Atherosclerosis, the control of saturated fat intake and its substitution with polyunsaturated fatty acids, precepts followed in both studies, are associated with cholesterol total and low-density lipoprotein cholesterol decrease, as well as with a decrease in cardiovascular events and death .
The comparison between the diets was also enabled by Davies et al. study , which compared the low glycemic index and calorie-restricted diets. As for the lipid profile, Davies et al.  verified that none of the groups presented a significant index reduction when compared to the initial evaluation. However, when the data was inserted in the forest plot, it shows that the low glycemic index diet was more favourable for high-density lipoprotein, low-density lipoprotein, and triglyceride improvement than the calorie-restricted diet. The type of diet did not affect the fatigue, quality of sleep, and disease activity as assessed through the British Isles Lupus Assessment Group. However, when the European Community Lupus Activity Measure evaluated the low glycemic index diet, its effect was favourable on fatigue. The study conducted by Davies et al.  shows that the low glycemic index diet redresses the postprandial hyperglycemia and hyperinsulinemia and the late postprandial hypoglycemia, which increases the risk of obesity, diabetes, and cardiovascular disease. The Update of the Brazilian Guideline on Dyslipidemias and Prevention of Atherosclerosis indicates as an adequate strategy for handling dyslipidemia diets such as the Mediterranean diet, emphasizing the importance of keeping a moderate-fat quantity, eliminating trans fatty acids, controlling the consumption of saturated fats, prioritizing polyunsaturated and monounsaturated fats, reducing sugars, and including lean meats, fruits, grains, and vegetables in the diet . It further stresses that high carbohydrate intake increases glycemia, which generates hyperinsulinemia. In turn, this condition activates the transcription factors that promote the synthesis of fatty acids and triglycerides. There is still no substantial evidence proving the effectiveness of the low carbohydrate diet on lipid profile, mainly because the studies diverge significantly on the low carbohydrate diet definition. The 2018 United Kingdom guidelines on diabetes show that long-term adherence to low carbohydrate diets is low .
It has been demonstrated in studies that medications such as hydroxychloroquine and prednisone may affect the lipid profile [18, 19]. Hydroxychloroquine seems to have a beneficial effect due to the reduction of atherogenic lipoproteins and prednisone is associated with a worsening in the lipid profile of patients with lupus activity . The studies included in this review did not differ between groups regarding the use of hydroxychloroquine and prednisone. It is important to note that the review evaluated patients with inactive disease and, probably, with low doses of these drugs.
Medeiros et al.  published a systematic review investigating the effects of nutritional supplements such as omega-3 and vitamin D, as well as the study by Islam et al. who recommends intake of Omega 3 and 6; vitamins A, B, C, D, and E; minerals (calcium, zinc, selenium, iron, and copper) and polyphenol-containing foods to produce an immunomodulatory effect in SLE patients , differing from the present study because the objective of the latter was to evaluate the nutritional diet impact, not a specific nutritional supplement. Regarding methodological aspects, the review by Medeiros et al.  restricted the search to the period from 2006 to 2016, and the exclusion criteria evaluated nutrients or diet analyses only. Furthermore, the systematic review did not describe the results regarding the effectiveness of the interventions.
Supplementation of macronutrients and micronutrients produces immunomodulatory effects in SLE patients, so the intake of Omega 3 and 6, vitamins A, B, C, D, and E, minerals such as calcium, zinc, selenium, iron, and copper, and polyphenol-containing foods are recommended.
Because dietary supplementation of various macro and micronutrients have exhibited immunomodulatory effects, including maintenance of homeostasis and improved physical and mental well-being in SLE patients, it is recommended that these patients consume a balanced diet that is low in calories and protein but contains plenty of fiber, PUFAs (ω3 and ω-6), vitamins (A, B, C, D, and E), minerals (calcium, zinc, selenium, iron, and copper), and polyphenol-containing foods.
The present systematic review is the first study about the nutritional diet impact on systemic lupus erythematosus patients and followed the methodological principles considered essential to conduct and report a systematic review, which includes conducting searches in several databases without date and language restriction, evaluating and selecting articles independently, and registering the protocol on PROSPERO.
Some limitations were found in this review. The small number of included studies and the small number of patients included can lead to a conclusion that does not correspond to reality. The different types of diets evaluated makes it difficult to standardize the studied intervention. This problem can be overcome by conducting studies with the involvement of several centres in a multicenter way. Also, the heterogeneity of the data makes it impossible to carry out a meta-analysis. Due to these limitations, further studies are needed to confirm the association between the impact of diet on patients with systemic lupus erythematosus.