Premenstrual symptoms affect up to 40 percent of women of reproductive age, with approximately 5 percent of women reporting symptoms sufficiently severe to disrupt work and normal daily activities. Because diet is known to influence serum sex-hormone levels, a great interest in dietary management of premenstrual symptoms has arisen. Low-fat and vegetarian diets reduce serum estrogen levels and have been reported to reduce menstrual pain in selected women. Barnard and associates studied the impact of a low-fat vegetarian diet on dysmenorrhea, premenstrual symptoms and serum sex-hormone concentrations.

Study participants were recruited through newspaper advertisements and notices in the offices of private gynecologists. To be included in the study, volunteers had to be at least 18 years of age and have menstrual periods characterized by moderate to severe abdominal pain causing significant distress and impaired social or occupational functioning. Volunteers were excluded if they had irregular menstrual cycles, significant medical illness, a history of hormone-related illness, recent use (within the previous six months) of oral contraceptives or a history of mental illness, including alcohol or drug abuse. After an initial history and physical examination, those who met the study criteria were randomized to one of two groups. Both groups completed two phases: an intervention diet for two cycles and their usual diet plus a placebo supplement for two cycles. The groups received the interventions in opposite order in a crossover design. No animal products, fried foods, avocados, olives, nuts or seeds were allowed in the intervention diet. Rather, the diet was rich in grains, vegetables, legumes and fruits, and adequate in all nutrients except vitamin B₁₂, which was recommended to be supplemented during the study. In addition, participants attended weekly support meetings during the study period, in which nutritional advice and grocery samples were provided. On day 6 of the cycle, blood samples were obtained to measure sex-hormone binding globulin, estrogen and serum lipid levels. Participants also completed a food diary for three days each cycle and a symptom diary from day 14 until the end of menstrual flow to record pain and other symptoms. The severity of pain was assessed using a 10-point scale. Body weight was assessed between days 14 and 21 of the cycle.

Fifty-one women enrolled in the study, but only 33 completed it; those who dropped out did so for a variety of reasons, including pregnancy and noncompliance with the intervention diet. Average participant age was 36 years (range: 22 to 48), and participants were predominately white (20), single (22) and nulliparous. Only two participants were current smokers. The duration of menstrual flow did not change during either phase of the study; however, the duration and intensity of menstrual pain decreased significantly in the invention diet phase. Participants' perceptions of other symptoms, specifically water retention, behavioral changes and difficulty concentrating, decreased during this phase as well. In addition, mean serum sex-hormone binding globulin levels increased and participant weight decreased during the intervention diet phase.

The authors conclude that a low-fat vegetarian diet significantly decreased symptoms and increased sex-hormone levels in women with premenstrual syndromes. These dietary changes could influence estrogen metabolism, and the high levels of omega-3 fatty acids found in vegetarian diets could influence prostaglandin metabolism, with consequent anti-inflammatory actions. However, the contribution of group support and the “placebo effect” of participation in the study is unclear.