Although a healthier diet, as defined by a higher adherence to the 2010 alternative healthy eating index (AHEI-2010), was associated with a reduced risk of RA, particularly seropositive, occurring at 55 years of age or younger [14], no association between long-term adherence to the AHEI-2010 and SLE risk was observed [15]. The AHEI-2010 was developed by researchers at the Harvard School of Public Health as an alternative measure of diet quality to identify future risk of diet-related chronic disease [17]. It includes a variety of foods/nutrients and defines fruits, vegetables, whole grains, nuts, long-chain n-3 polyunsaturated fatty acids (LC-PUFAs), and moderate alcohol consumption as healthy items, while sugar-sweetened beverages, red/processed meat, trans fat and sodium intake are classified as unhealthy components. As far as AHEI-2010 subdomains are concerned, a higher score of alcohol (moderate intake) or red meat consumption (lower intake) was significantly associated with a reduced RA risk regardless of body mass index (BMI). Conversely, women in the highest AHEI-2010 tertile of nut/legume intake had a decreased risk of developing SLE compared to those in the lowest tertile, but no other association was observed [15].

The data on alcohol consumption and RA are in line with a recent meta-analysis of prospective studies demonstrating that low to moderate intake is inversely associated with the development of RA in a dose, time and gender-dependent manner [18].

On the contrary, the link between alcohol consumption and SLE risk remains controversial. A meta-analysis conducted in 2008 demonstrated that moderate alcohol intake had a protective effect on the development of SLE [19], and the subsequent studies were in line with the previous literature [20,21,22,23]. However, no genetic association in this regard has been identified [24]. Furthermore, no association for a higher risk in heavy alcohol consumers was reported by other studies [25,26].

Other dietary quality scores have also been explored in relation to the risk of RA or SLE onset in the NHS and NHS II cohorts.

The Mediterranean diet is a dietary pattern based on whole or minimally processed foods and a high intake of vegetables, fruits, whole grains, fish and olive oil, with moderate consumption of red meat and wine. The adherence to the Mediterranean diet proved to be effective in preventing metabolic diseases such as diabetes and CV diseases [27,28,29]. The alternate Mediterranean diet (aMed) score is a modified version of an existing Mediterranean diet scale containing nine components including vegetables (not potatoes), fruits, nuts, whole grains, legumes, fish, the ratio of monounsaturated to saturated fat, red and processed meats and alcohol [30]. Greater adherence to a Mediterranean dietary pattern, as measured by the aMed score, did not affect the risk of developing RA or SLE [15] in healthy individuals.

The Dietary Approach to Stop Hypertension (DASH) is a healthy dietary pattern focused on eight components: high intake of fruits, vegetables, nuts and legumes, low-fat dairy products and whole grains, and low intake of sodium, sweetened beverages and red and processed meats [31]. Although previously evaluated only in metabolic diseases, including gout, the recent evidence of a pivotal role of sodium in the induction of autoimmunity led investigators to also explore this pattern in RA and SLE; however no direct association with the risk of developing either disease was demonstrated [15].

The empirical dietary inflammatory pattern (EDIP) includes different foods based on their association with plasma levels of inflammatory biomarkers (including C-reactive protein and IL-6) [32]. The nine anti-inflammatory groups include beer, wine, tea, coffee, dark yellow vegetables, leafy green vegetables, snacks, fruit juice and pizza. The nine pro-inflammatory groups include processed meat, red meat, organ meat, non-dark meat fish, other vegetables, refined grains, high-energy beverages, low-energy beverages and tomatoes. In RA, increasing EDIP scores (namely, most inflammatory dietary intake) were associated with increased risk of seropositive RA among women aged 55 years or below [16]. Conversely, no association between EDIP scores and SLE risk was observed [15].

A detailed analysis of the NHS and NHS II cohorts with regard to the intake of antioxidants from foods and supplements was also conducted; however, it ruled out any protective effect of both the range of antioxidant intakes and of the overall antioxidant intake on the risk of developing RA or SLE [33]. Moreover, it was reported that omega-3 fatty acids could prevent the development of RA, improve muscle metabolism and reduce muscle atrophy in subjects at high metabolic risk [34].

The existing literature does not allow any definitive conclusions to be drawn either in favor or against a role of diet in the risk of developing SLE onset. However, with the only exception of alcohol consumption, studies on other nutrients as well as on dietary patterns are still too few. Therefore, any association (or lack thereof) deserves to be further explored, focusing also, for example, on the possible interaction between food and microbiome, given its role in SLE pathogenesis [35].