Avoiding foods that contain nickel significantly decreased body fat and body-mass index in overweight women allergic to the metal, especially those in early menopause, according to a pilot study in PLoS One.

The study found an unusually high prevalence of nickel allergy in women and men who were overweight or obese compared with the general population. Nickel, a trace element found in water, soil and food, is the most common cause of metal allergies. Foods that contain high levels of nickel include whole grains, legumes, cocoa and some vegetables, the study said.

Researchers recruited 87 patients, mostly women, in their early 50s from the allergy unit of the Italian Red Cross in Rome. Their average BMI was 32, or obese.

Nickel allergies were diagnosed in 60% of the women and 13% of the men. Nickel allergy affects approximately 13% of women and 2% of men in the general population, researchers said.

The allergic subjects were prescribed a balanced, normal-calorie diet that eliminated or restricted foods containing higher concentrations of nickel. After six months, 56% of women following the diet had lost 5.1% of their body fat, trimmed 4.6 inches from their waistlines and saw their BMIs drop by 4.2 points. Men were excluded from the final analysis because of their small numbers, researchers said.

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