Until two decades ago, the prevailing clinical impression among  dermatologists  was that of a relationship between acne and diet. For many years - until around 1970 - dermatologists told their patients to avoid certain foods, especially pork fat, choclate, nuts etc. Chocolate, in particular, was incriminated as an aggravating factor of acne, but in 1969 a double-blind study demonstrated that enriched chocolate did not affect the clinical severity of acne.25 A review of the papers on chocolate and acne26 has concluded that, with one  exception,25  the reports were essentially anecdotal, and often presented inadequately controlled experimental data. The general trend  of recent studies  favours the  impression that chocolate ingestion is irrelevant to the causation of acne vulgaris. A review article in the Journal of the American Medical Association summarizing the  current thinking on the pathogenesis and treatment of acne states, 'Diet plays no role in acne treatment in most patients ... even large amounts of chocolate have not clinically exacerbated acne.

  Iodides have also been blamed for aggravating acne but  the evidence for this is rather poor.  A tenuous association has been found between dietary iodides and the prevalence of  cystic  acne and  scarring.28 As  yet there is no evidence incriminating fluorides, which are now added in some parts of the world to toothpaste and to drinking water.

  Experimentally, relative extremes of dietary manipulation  can modify sebaceous  gland function. In obese and non-obese subjects, low-calorie diet produces a rapid decrease in  sebum excretion rate, a change which is noticeable within 7-10 days. At the same time there is also a change in the biochemical composition of the surface lipids with an increase in squalene and a decrease in other major lipid classes of  sebum. When adult  obese  subjects were  given  a  low-calorie diet (800-1,000 kcal/day), there was a significant reduction in the urinary  excretion of  dehydroepiandrosterone (DHA) and urinary  androsterone.31  Total food  withdrawal resulted in an almost complete disappearance of DHA sulphate, androsterone sulphate  and etiocholanolone sulphate.

  A 1987 study investigated the relationship between acne  severity  and  diet (DeLoy A and  Cunliffe WJ, unpublished work 1987).  One hundred acne subjects were interviewed by a dietitian to establish their eating habits. (The  interviews were  conducted two  months into therapy to prevent bias by the subjects' facial acne; the interviewer  did not see the patients' trunk.)  On computer  analysis no link was found  between acne severity and total caloric intake, carbohydrates, lipids, proteins, minerals, amino acids or vitamins. Nor was there any correlation between acne severity and types of food ingested. Thus, it seems unlikely that the dietary manipulation will significantly modify the acne process.