Table 2.

Outcomes of the included studies

SStudy	Assessment of adherence to the MD	Assessment of acne severity	High adherence to the MD in the control group N (%)	High adherence to the MD in the case group N (%)	Association between adherence to the MD and acne development (i.e., differences between case and control groups)	Association between adherence to the MD and acne severity	Association between items of the MD and acne development
Skroza (2012) [40]	80-item, 9-level food-frequency questionnaire	Not assessed	39/200 (19.5)	5/39 (5.4)	- cOR = 0.22 (CI 95%, 0.08–0.64) - aOR (full model*) = 0.30 (CI 95%, 0.10–0.85) - aOR (backward elimination model) = 0.31 (CI 95%, 0.11–0.89)	Acne severity was not assessed	Not reported
Barrea (2021) [41]	MEDAS	GAGS	37/51 (72.5)	22/51 (43.1)	- Compared to controls, patients with acne showed lower adherence to the MD overall (p <.001), with a higher percentage of cases in the low adherence category (17.6% vs. 0.0%, p =.005), and a lower percentage in the high adherence category (39.2% vs. 27.5%, p =.293). - No multivariate analysis was conducted.	- Bivariate analysis: acne severity (categorical) was significantly associated (p =.007) with adherence to the MD (numerical). - Correlation analysis: r = −.504, p <.001* - Multiple regression analysis*: β =− 0.504, p <.001	- Olive oil as main lipid (p =.318); olive oil (p =.795); vegetables (p =.026); fruits (p =.008); red meats (p =.065); butter, cream, margarine (p =.194); soda drinks (p =.034); wine (p =.311); legumes (p =.041); fish/seafood (p <.001); commercial sweets (p =.021); nuts (p =.003); Poultry more than red meats (p =.051); use of sofrito sauce (p =.686).
Bertolani (2021) [42]	MEDAS	GAGS	Not reported	27/35 (77.1)	Not reported	Adherence to the MD decreased with increasing acne severity but this was not significant (data are not reported)	Not reported
Ah-Thiane (2022) [43]	MEDAS	GEA	Not reported	Not reported	N/A* *Authors conducted an erroneous correlation analysis between adherence to the MD and acne severity where control participants were included (r = −.47; p <.001), as participants without a disease cannot be assigned a “severity score”	- Correlation analysis: r = −.32; p =.047* - Linear regression analysis*: multiple regression coefficient = − 0.17; p =.017*	Not reported
Taha (2024) [44]	MEDAS	GAGS (unblinded assessor)	27/121 (19.8)	24/121 (22.3)	- cOR = 0.86 (CI 95%, 0.46–1.60) - aOR (full model*) = 0.70 (CI 95%, 0.34–1.37) - aOR (backward elimination model*) = 0.88 (CI 95%, 0.47–1.62)	- Correlation analysis: r = −.07; p =.414 - Participants with mild acne had a lower rate of high adherence to the MD than participants with moderate-to severe acne (18.7% vs. 23.3%, p =.579)	Olive oil as main culinary lipid (p =.882); olive oil (p =.890); vegetables (p =.022*); fruits (p =.724); red meats (p =.894); butter, cream, and margarine (p =.322); soda drinks (p =.377); legumes (p =.480); fish/seafood (p =.641); commercial sweets (p =.291); nuts (p =.399); consuming poultry more than red meats (p =.193); use of sofrito sauce (p =.162)

*Model variables:

Skroza (2012): sport activity, smoking status, familial diabetes status, familial hypertension status, familial hypercholesterolemia status, and MD score

Barrea (2021): model variables: anthropometric measurements, body composition, and adherence to the MD

AH-Thaine (2022): age, BMI, smoking, alcohol consumption, family history of acne, dairy product consumption, sugar consumption, snaking, use of cosmetics, previous local treatment, previous systemic treatment

Taha (2024): family history, milk consumption, smoking, and adherence to the MD (full model); family history and adherence to the MD (backward model)

*Abbreviations: MD: Mediterranean diet; N/A: nonapplicable; MEDAS Mediterranean Diet Adherence Screener; GAGS: Global Acne Grading System; GEA: Global Acne Evaluation