Acne is a disease of the pilosebaceous units in the skin, and it is considered to be the most common disease affecting all age and ethnic groups . During the course of the last 30–40 years, a general consensus has emerged within the dermatology community that diet has no role in the etiology of acne . Yet, earlier reports investigating the impact of diet on acne had controversial results, with some indicating that a diet rich in carbohydrates and fats worsens acne , and others postulating certain food items to be associated with acne, including milk and other dairy products, chocolate, cereal, bread, nuts, eggs, and pork . Although the results of case series have not consistently supported any dietary factor, yet the current consensus among dermatologists is to advise acne patients to avoid foods that they believe precipitate or worsen the condition .
A large body of evidence now exists showing how certain foods and food substances may directly or indirectly influence follicular keratinocyte proliferation and differentiation, inflammation, and the balance of steroid hormones, and hence sebum synthesis. Dysregulation of these three fundamental physiologic mechanisms along with the involvement of Propionibacterium acnes represent the known causes of acne .
Foods with a high glycemic index/glycemic load (GL) tend to increase blood glucose levels with subsequent hyperinsulinemia, which elicits endocrine responses promoting unregulated tissue growth and enhancing androgen synthesis, which finally affect the development of acne through mediators such as androgens, insulin like growth factor-1 (IGF-1), insulin like growth factor binding protein-3, and retinoid signaling pathways . IGF-1 is present in ordinary milk ; ingesting milk also stimulates endogenous IGF-1 production . The development of hyperinsulinemia and insulin resistance elicits a pathological rise in serum concentrations of nonesterified free fatty acids , causing overexpression of the epidermal growth factor receptor , which when stimulated in keratinocytes, leads to increased keratinocyte proliferation and decreased keratinocyte apoptosis, thus contributing to the pathogenesis of acne .
Milk also contains placenta-derived progesterone and other dihydrotestosterone (DHT) precursors, including 5α-pregnanedione and 5α-androstanedione. These compounds are only a few enzymatic steps away from DHT (the accepted prime acnegen), and the enzymes required to mediate the change are present in the human pilosebaceous unit . In addition, some of these compounds have already undergone 5α-reduction in the bovine mammary gland with no need for further 5α-reduction . Elevated production of testosterone may be the result of dietary intake through a reactive rather than an absorptive mechanism. The elevation in blood glucose with the subsequent rise in insulin and IGF-1 cause a rise of blood testosterone and a decrease in sex hormone binding globulin levels, this results in presenting the pilosebaceous units with more testosterone .
The association between milk intake and acne was the strongest for skimmed milk. It is speculated that skimmed milk processing may have altered the relative bioavailability of bioactive molecules or their interactions with binding proteins. Moreover, whole milk contains more estrogen than skimmed milk, and estrogens tend to reduce acne. It is possible that the altered balance of hormonal constituents of skimmed milk rendered it more comedogenic . The iodine content of milk may also be playing a role in the development of acne. It is well established that iodine intake can exacerbate acne , and various studies have shown significant levels of iodine in milk in different countries including the United States, Britain, Denmark, Norway, and Italy .
Diet is also a well-known modulator of the systemic inflammatory response. One of the most important dietary factors that influence inflammation is the relative intake of omega-6 (ω-6) and ω-3 polyunsaturated fatty acids . Epidemiologic studies show that communities that maintain a diet high in ω-3 fatty acids, such as fish and seafood, have low rates of acne . The intake of ω-3 fatty acids has been shown frequently to suppress interleukin 1β (IL-1β) , IL-1α, tumor necrosis factor-α, IL-6, and IL-8 in peripheral blood monocytes . The suppression of IL-1α by dietary ω-3 polyunsaturated fatty acids may positively influence corneocyte differentiation by preventing or attenuating the hypercornification and scaling that occurs during microcomedogenesis. In addition, dietary ω-3 fatty acids are also known to inhibit synthesis of the proinflammatory eicosanoids prostaglandin E2 and leukotriene B4 .
Patients and methods
One hundred patients with acne vulgaris attending the Dermatology Outpatient Clinic at Cairo University Hospitals were recruited for this study. The study was conducted over a time of 6 months from February 2009 till the end of July 2009. The study included:
(1) Development of the questionnaire form by the dietitian, which was used to cover the following areas:
- (a) Interview for personal and social information;
- (b) Medical information including, menstrual irregularities, hirsutism, onset and duration of acne, drug intake, and family history of acne;
- (c) Main dietary habits including questions to detect the main meal, regular and neglected meals, eating between meals, eating at home or not, and the most common method used for food cooking;
- (d) Food frequency sheet containing 32 food items was given to all patients. Participants were asked whether or not these types of food were consumed and how frequently they consumed a typical portion size of these foods on average. A commonly used portion size was specified for each food (e.g. slice, piece, dessert spoon, spoonful, water glass) .
To rate how many times per day, week, and month they generally used to consume each item, we used the terms, frequently (1–4 daily), moderately (2–4 weekly), minimally (once weekly, 1–3 monthly), and no intake (<once monthly, rarely, and no consumption).
The food items were calculated by knowing the serving size of each with the help of the nutrition expert. The 32 items were grouped into nine main food categories such as milk and dairy products, fats, carbohydrates, high biological value proteins, beverages, nuts, chocolate candy, and salty food.
(2) Clinical examination was conducted to evaluate the type and severity of acne lesions whether mild: comedones and papules; moderate: comedones, papules and pustules; and severe: all of the above plus nodules and cysts.
(3) Blood samples were collected for all patients after fasting for 12 h for analysis of serum cholesterol and triglycerides. When both or one of the above were elevated, we analyzed high-density lipoproteins and low-density lipoproteins.
All data obtained were transferred to the statistical package for the social sciences version 15 (IBM Co., New York, USA) for analysis. Data were summarized using mean, standard deviation, and range for quantitative variables, numbers, and percent for qualitative variables. Comparisons between groups were made using χ2-test and Fissure's exact test for qualitative variables and analysis of variants with multiple comparison Post hoc test for normally distributed quantitative variables, whereas nonparametrical Kruskal–Wallis test and Mann–Whitney test were used for quantitative variables that are not normally distributed. Nonparametrical correlations were made to test, using Spearman's test, for linear relations between severity of acne and frequency of consumption of different food items. P values equal or less than 0.05 were considered statistically significant.
The demographic data of the patients are shown in Table 1. Out of the 84 female participants, only 19 (22.6%) had menstrual irregularities and 10 (11.9%) had hirsutism and androgenetic alopecia. Positive family history of acne was found in 49 (49%) patients, and only 34 (34%) participants were on therapy for acne.
Fifty-four percent of the participants were diagnosed with moderate acne, whereas severe acne was reported in 17% of patients and mild acne in 29% of patients. The clinical data of the studied acne patients are shown in Table 2.
Severe acne lesions tended to run for longer durations (P=0.006), but no statistical significant relationship between the degree of acne in the studied patients and the sex (P=0.130), residence (P=0.895), marital status (P=0.923), mean age (P=0.999), or weight (P=0.244) was found.
Female patients with hirsutism showed higher degrees of acne compared with those not suffering from hirsutism (P=0.006) (Fig. 1), but no statistical significant relationship between the degree of acne in the studied patients and the presence of menstrual irregularities was detected (P=0.825).
No statistical significant relationship was found between the severity of acne and the dietary habits of the studied patients including, whether the patients were eating three meals/day or not (P=0.454), skipping any meals (P=0.153), eating between meals (P=0.394), preferring boiled food (P=0.213), fried food (P=0.898), grilled food (P=0.312), spicy food (P=0.743), or salty food (P=0.454).
Only eighty-seven patients out of the 100 patients included in this study completed their lipid profile. The results are listed in Table 3. No statistical significant relationship was found with regard to the mean level of serum lipids and acne severity, including serum cholesterol (P=0.781), triglycerides (P=0.630), high-density lipoprotein (P=0.432), or low-density lipoprotein (P=0.103).
Correlation between the degree of acne and the types of food consumed
Milk and milk products
No significant correlation was detected between the severity of acne lesions in the studied patients and their consumption of milk and dairy products when calculating them together as one item or when we studied each item of the dairy products individually whether full cream, skimmed milk, powdered milk; white full cream, skimmed white cheese, other types of cheese, yoghurt, ice cream, butter, or cream.
Fats and oils
No significant correlation was detected between the severity of acne lesions in the studied patients and their consumption of fats and oils.
Fruits and vegetables
A statistical significant negative correlation between the frequency of consumption of fresh vegetables and severity of acne lesions was detected (r=−0.219, P=0.028) (Fig. 2).
A statistical significant positive correlation between the frequency of consumption of nuts and the severity of acne lesions was found (r=0.265, P=0.008) (Fig. 3).
A statistical significant positive correlation between the frequency of consumption of chocolate candy and the severity of acne lesions was found (r=0.236, P=0.018) (Fig. 4).
A statistical significant positive correlation was found between the frequency of consumption of red tea and the severity of acne lesions (r=0.203, P=0.043) (Fig. 5).
No correlation between the frequency of intake of pickles and acne severity was found.
Diet is directly implicated as the most likely environmental factor underlying the development of acne. Confirmation of the diet-acne hypothesis requires numerous well-controlled dietary interventions examining multiple nutritional factors . The analysis of the food frequency questionnaire in this study linked certain foods to acne flares in some acne patients. The increase in the consumption of nuts, chocolate candy, and red tea was associated with more severe forms of acne, whereas the consumption of fresh vegetables seemed to be associated with milder forms of acne.
Chocolate candy consumption was associated with higher degrees of acne in our study. Although chocolate consumption was long discriminated as an important exacerbator of acne, all the studies conducted by Fulton et al. , Cordain , Adebamowo et al. , and Adebamowo et al.  found no associations between acne and intake of chocolate bars. Nevertheless, chocolate candy may contain many other ingredients in addition to cocoa solids, such as cocoa, butter, sugar (usually sucrose), nonfat milk solids, milk fat, an emulsifier (usually lecithin), and flavoring agents (usually vanilla). Accordingly, any of the remaining ingredients in chocolate candy, either individually or in combination with one another, cannot be ruled out in the etiology of acne .
The positive correlation between frequency of consumption of nuts and the severity of acne lesions in our patients could be attributed either to the salt content or the high caloric value of nuts. However, these findings are different from what have been found by Anderson  who noticed that acne patients, who reported that nuts exacerbate their acne, showed no change in their acne severity when they were fed large quantities of nuts for 1 week.
We tested salt consumption, represented by pickles, to demonstrate its role as one of the important types of food implicated in acne pathogenesis, and found no correlation between the frequency of consumption of pickles and the severity of acne in our patients.
The caffeine content of tea could be the reason behind the positive association between the consumption of tea in our patients and severe forms of acne. However, no significant correlations were found with regard to other types of caffeine-containing beverages, such as instant coffee and Turkish coffee, and acne severity in our study. Yet, it is to be noted that these beverages were only consumed by a very small number of patients.
Although milk is now considered to be the most implicated food in the exacerbation of acne lesions, we did not find significant correlations between the severity of acne lesions in our patients and their consumption of milk and dairy products when calculating them together as one item or when we studied each item of milk and dairy products individually. These findings are different from those of Robinson , Adebamowo et al. , and Adebamowo et al.  who established a positive association between the intake of milk, especially skimmed milk, and the severity of acne. The difference between our findings and the findings of other researchers may be attributed to the fact that milk was not frequently used by our patients as 42% of the patients were rarely or were not consuming full cream milk at all and skimmed milk and skimmed cheese are not commonly consumed in Egypt (only 7% of our patients consumed skimmed milk and only 5% consumed skimmed cheese).
Although the belief that the consumption of fats may be associated with acne is supported by many dermatologists , no correlation was detected between the frequency of consumption of fats and oils and the severity of acne lesions in our patients, and this was also found by Adebamowo et al. .
The relationship between the intake of fresh vegetables and acne, to our knowledge, was not studied before in the literature. The significant negative correlation between the frequency of consumption of fresh vegetables in our patients and acne severity indicates that the more the fresh vegetable consumption, the less the severity of acne lesions. Therefore, it seems that fresh vegetables may have a protective role against acne flares. This may be attributed to the antioxidants present in fresh vegetables or the low caloric values of vegetables, but on the other hand, no significant correlations were found between the frequency of consumption of cooked vegetables or fresh fruits and acne severity.
High GL foods are known to increase blood glucose levels with subsequent hyperinsulinemia, which elicits endocrine responses promoting unregulated tissue growth and enhancing androgen synthesis, which finally affect the development of acne . However, we did not establish a correlation between the severity of acne in our patients and the frequency of consumption of different types of carbohydrates, such as cereals, pulses, sweets, and sugars. These findings are in concordance with those found by Kaymak et al. , but are different from those of Smith et al.  who found that the total and inflammatory acne lesion counts decreased after the consumption of an experimental low GL diet, compared with the acne counts in patients consuming a conventional high GL diet. In addition, the hormonal profile of the low GL diet group improved, as measured by significant declines in dehydroepiandrosterone sulfate and the free androgen index.
On account of the concurrent presence of insulin resistance with obesity, it might be expected that acne incidence may be more prevalent in the obese individuals. However, no significant relationship was found with regard to the mean weight of our patients and the degree of their acne (P=0.244), and this confirms the findings of Kaymak et al. , Adebamowo et al. , and Adebamowo et al.  who reported no significant relationship between the patients' degree of acne with respect to BMI as a measurement of adiposity. Moreover, the absence of a significant relationship between the lipid profile of the patients and acne severity indicates that serum lipid abnormalities have got no relationship with the development of acne lesions.
Moreover, the different food habits practiced by our patients, such as eating regular meals or skipping meals, eating between meals, and the most used method for food cooking whether boiled, fried, grilled, spicy, or salty, were not linked to the degree of their acne. This is in contrast to the general belief that fried foods with high content of fats and salty foods exacerbate acne lesions .
In support to the relationship between hormonal imbalance and the development of acne, the female patients in our study complaining of hirsutism had severe forms of acne compared with those not suffering from hirsutism. DHT has been proved to mediate androgen-dependent skin diseases, such as acne, hirsutism, and androgenetic alopecia .
In conclusion, we could presume that certain foods may be implicated in acne flares in certain acne patients. Such foods, when eliminated from the diet of these patients, could influence the outcome of acne management.
In this study, we demonstrated that the increase in the consumption of nuts, chocolate candy, and tea was associated with more severe forms of acne, whereas the consumption of fresh vegetables seemed to be associated with milder forms of acne.
There is no conflict of interest to declare.
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