At the moment, information regarding the impact of diet on autoimmune diseases is yet insufficient. However, caloric restriction was proven to induce various benefits to the immune system, since this restriction also leads to changes in the gut microbiota (5).

Obesity among SLE adults is a real concern, since up to 40–50% of these patients are obese and more prone to suffer from fatigability (9–11). For this group of SLE patients, losing weight by keeping a low glycemic index or a low-calorie diet also proved to be efficient in lowering the level of fatigue, though the disease activity was not influenced by diet (12).

Reducing the caloric intake has helped to prevent the disease progression and the antiphospholipid syndrome in mice. In humans, one study monitoring the dietary impact of two isocaloric diets on SLE emphasized that the diet with higher level of polyunsaturated fatty acids (PUFA) reduce the risk of fetal loss and symptoms in women with SLE and antiphospholipid syndrome (13).

Strong evidence supports the idea that hypocaloric diet is positively related to disease activity. Therefore, the adequate caloric ratio for women is around 1,000–1,200 kcal/day and for men 1,200–1,400 kcal/day, with special regards to obese patients or with a tendency towards obesity, as well as SLE patients undergoing long-term or high-dose corticotherapy (14).

Other lifestyle habits that may help alleviate symptoms in SLE enclose smoking cessation and physical exercise, preferably aerobic, since it is safer (15). It may also be useful for patients with SLE to benefit from individualized nutrition counseling, which was shown to be effective in initiating dietary changes (16).

In patients with stable disease a diet rich in polyunsaturated fatty acids may have a positive impact on overall clinical status (15). Omega-3 fatty acids, such as eicosapentanoic acid and docosahexanoic acid, elicit an anti-inflammatory effect by decreasing the level of C reactive protein (CRP) and other inflammatory mediators (17,18). Caloric restriction and well-established diet supplementation with omega-3 PUFA, eicosapentanoic acid and docosahexanoic acid (at a ratio of 3:1), regulates levels of total cholesterol, LDL-C and TG. Apart from the anti-inflammatory effect, adding omega-3 PUFA in SLE patients diet protects against free radicals and helps defend cardiovascular alteration by reducing the level of antibodies (anti-dsDNA), interleukins (IL-1α, IL-1β, IL-2) and TNF-α, and regulating proteinuria and blood pressure (6,18). Other omega-3 acids like α-linolenic acid and Υ-linolenic acid also have beneficial effects by limiting TNF-α and IL-2 secretion. No downsides of introducing omega-3 PUFA to SLE patients' diet were found, as opposed to omega-6 PUFA supplementation, which may exacerbate SLE activity (6).

The main sources for omega-3 PUFA are krill oil, fish oil, olive oil, canola oil, flaxseed oil, fish (salmon, tuna, sardine, herring), but it may be found in primrose oil and soybean oil (6,19). Krill oil extracted from the Antarctic krill is considered superior to fish oil since it contains a higher amount of omega-3 PUFA and it has an antioxidant effect, reducing the inflammatory joints infiltrate (19).

With a concentration of 70% omega-3 PUFA and rich in α-linolenic acid, flaxseed oil daily intake of 30 g can lower serum creatinine in SLE patients with renal dysfunction (6,20). High dosage of fish oil (18g/day) is also beneficial in reducing TG level to up to ~40%, while increasing HDL-C by a third (21,22).

Omega-3 PUFAs inhibit leukocyte chemotaxis, adhesion molecule expression and production of inflammatory cytokines, through the action of specialized pro-resolving mediators, such as lipoxins, resolvins, protectins, and maresins, which reduce inflammation (23). Eicosapentaenoic acid and docosahexaenoic acid, omega-3 fatty acids found in oily fish, are able to partly inhibit inflammation, but further clinical trials are required to see their effects on SLE. Dose-dependent actions of marine n-3 PUFA on inflammatory responses have not been well described, but it appears that at least 2 g/day is necessary to achieve an anti-inflammatory effect (24).

Moderate protein intake of 0,6 g/kg/day is useful for improving renal function in SLE patients (25) and mouse studies led to the conclusion that a limitation in consumption of phenylalanine and tyrosine could also be of some benefit (25,26). The major sources of proteins are meat and eggs.

The daily intake of fibers found in whole cereals, fruits and vegetables, should be around 38 g for men and 25 g for women, in order to reduce post-prandial glycemia and lipids level, regulate hyperlipidemia, and lower blood pressure and C reactive protein. As far as fiber consumption is concerned, adequate water intake should be considered, and exceeding fiber intake has to be avoided because it can lead to low absorption of nutrients (6).

Vitamin D is a steroid hormone with essential role on mineral metabolism and immune system homeostasis, and its deficiency has been associated with a higher susceptibility of SLE and more severe disease activity, especially in patients with dark skin (2,3).

Medical data show that the active form of vitamin D (calcitriol) may boost the innate immune response, regulating the T and B cell responses. Therefore, a lower level of vitamin D can be a risk factor for triggering not only SLE, but also other autoimmune diseases (27,28).

Sunlight exposure is known to stimulate vitamin D production, but this elicits a controversy since SLE patients have photosensitivity. Patients with SLE are advised to use sunscreens daily even if they do not see the sun, ~80% of UV penetrates the clouds and the fog (29). In this case, dietary supplementation of vitamin D may be beneficial (30). In fact, some studies postulate that high doses of vitamin D (up to 50,000 IU/day) have a preventive role, but similar improvements were obtained with doses of 2,000 IU/day (2,31).

According to Antico et al (28) several studies revealed that the level of vitamin D in SLE patients was <30 ng/ml in 56–75% of cases, whereas the same low level was found at a lower rate in healthy individuals (36–55%). This may be due to the fact that SLE patients avoid sun exposure. Ritterhouse et al (27) stated that healthy individuals with positive ANA have a higher predisposition to vitamin D deficiency than ANA negative persons.

Low levels of vitamin D are associated to high score of SLE activity-SLEDAI (32). Vitamin D supplementation brings significant beneficial effects on bone mineral density if it can reach a plasma level of >36,8 ng/l (30) but also on dendritic cells maturation and activation (33).

Several studies conducted on vitamin D supplementation (2 µg/day of cholecalciferol and/or alfacalcidol) have not proven any improvement in the clinical outcome of patients, nor in reducing the frequency of lupus flares (28). There was also a study aimed to examine whether vitamin D supplementation in adolescence can influence adult onset of SLE, but no associations were found (34).

In addition, one study suggests that a high level of vitamin D can also help against fatigability in SLE patients (35). However, several other studies have shown that vitamin D supplementation does not improve fatigue in SLE patients (36,37).

Vitamin E, especially combined with omega-3 PUFA from fish oil, decreases levels of inflammatory cytokines, IL-2, IL-4 and TNF-α (6).

Vitamin C, an important antioxidant, prevents oxidative stress, reduces inflammation and lowers antibodies levels (anti-dsDNA, IgG), also preventing cardiovascular complications. Therefore, vitamin C should be supplemented in SLE patients diet at a maximum dose of 1 g/day, or in combination with vitamin E (vitamin C; 500 mg and vitamin E; 800 IU), due to its synergic action. Orange juice, tangerine, papaya and broccoli are excellent sources of vitamin C (6).

Retinoic acid, a vitamin A metabolite, has antineoplastic effect, inhibits Th-17 and reduces antibodies level, and therefore diet supplementation should include 100,000 IU vitamin A daily, with caution not to exceed this dosage, causing symptoms that range from dry skin, alopecia, headache, nausea and anemia, to death (6,21). Natural sources of vitamin A include mainly carrots and pumpkins, but it can be found in spinach, sweet potato and liver (6).

The vitamin B complex helps reduce the level of TG and LDL-C, and improves clinical symptoms in SLE. The best food supply for vitamin B is red meat, liver and fortified cereals, but it can also be found in chicken, salmon, sardine, nuts, eggs, banana, and avocado (6).

Little information is known about polyphenols, bioactive components of a wide range of food, such as fruits and vegetables, red wine and tea, with a highly beneficial impact on the gut microbiota (12).

A recent study was set to determine the associations between polyphenols intake and fecal microbiota in patients with SLE and in controls (38).

Flavonoids represent the largest class of polyphenols and are classified in six subclasses including flavones, flavonones, flavonols, chalcones, anthocyanins and isoflavonoids. These incredible health boosters, apart from promoting a better immune response, have a well-established antioxidant and antimicrobial effect, as well as an antiaging role (39).

The main food that provide an intake of flavones include various fruits and vegetables (oranges, lettuce, watermelon, kiwi, tomato, apple, lentils, celery). The study of Cuervo et al (38), showed oranges provide the main amount of flavonones in SLE patients, while dihydrochalcones were ensured merely from apple intake. Dihydroflavonols came predominantly from consumption of red wine, whereas flavonols intake was due to tea, apple, spinach, walnut, white bean, lettuce, asparagus, broccoli, green bean and tomato. The study points out that a well-balanced diet, with a high intake of apples and oranges, as well as other fruits and vegetables rich in flavonoids, has been associated with the fecal levels of beneficial microorganisms (Lactobacillus, Blautia and Bifidobacterium) in SLE patients (38).

Isoflavones are estrogen-like nutrients, extracted from soybean, which have an antiinflammatory and antioxidant effect, reduce proteinuria and antibodies production, and can decrease IFN-Υ secretion (39). Other sources of isoflavones are black beans, olive oil and cereals (6).

Special attention is to be paid to mineral intake since it is best to restrict consumption of some minerals such as zinc and sodium. It was emphasized that a decrease in zinc can improve symptoms in SLE patients and also reduce levels of antibodies (anti-dsDNA) (22). Zinc is particularly found in mollusks, but also in milk, soybean and spinach (6).

Sodium intake not only has no beneficial effect but also exacerbates renal dysfunction (40) in SLE patients, who should be advised to reduce salt and condiments from their diet. For these patients, sodium intake should be less than 3 g/day (41).

Selenium has antioxidant and anti-inflammatory effects and can be added to patients' diet from consumption of nuts, whole cereals, eggs and ricotta (6). Calcium levels can be increased by the intake of diary, spinach, sardine or soybean, but oral supplements are also of use (Calcium >1500 mg daily, in addition to vitamin D; 800 IU vitamin D) in order to help prevent bone mass loss. Iron should only be used in anemic patients, to maintain a balance, since excess of iron can aggravate renal impairment in SLE patients and a deficiency exacerbates clinical symptomatology (6).

Conflicting results have emerged concerning L-canavanine, a non-proteicaminoacid that controls antibodies synthesis and has a suppressive effect on T cells. The main source for L-canavanine are soybean and alfalfa, but it can also be extracted from onion (6). Some studies revealed that alfalfa sprouts induced lupus-like syndrome in otherwise healthy individuals and reactivated SLE both clinically and serologically in patients with inactive disease (42).

Taurine, found in meat, eggs and oyster, is a β aminoacid which regulates the immune response, decreases the oxidative stress and lowers the level of inflammatory cytokines and lipids (6).

Royal jelly, rich in aminoacids and vitamins, could supplement SLA patients' diet, due to its hypocholesterolemic, anti-inflammatory and immunoregulatory effects (43).

Over the past decades, curcumin, a polyphenol extracted from a spice called Curcuma longa, also known as turmeric, has been highly studied in both pre-clinical and clinical trials (44). Due to its well-established anti-inflammatory, antioxidant, antibacterial, hypoglycemic and wound healing effects (45,46) curcumin has been used in a wide range of inflammatory diseases including the dermatological spectrum (psoriasis, vitiligo, SLE- lupus nephritis, oral lichen planus) (44).

The recommended dosage for lupus nephritis is 500 mg daily for 3 months, which leads to a reduction in proteinuria, hematuria and blood pressure in SLE patients who have relapsing of intractable lupus nephritis (47). Curcumin modulates pro-inflammatory cytokines, adhesion molecules and CRP, thus eliciting a beneficial anti-inflammatory effect in arthritis, by reducing pain and CRP level, and increasing the walking distance, at a dosage of 200 mg daily for 3 months (48,49). When used in combination with celecoxib (COX-2 inhibitor), the effect is synergic (50). The dosage for SLE ranges from 100–200 mg daily to 4.5 g/day, but curcumin supplementation is considered safe in up to 12 g daily (44).