Garlic has been advocated as a remedy for the treatment and prevention of a variety of health problems. Its cardioprotective effects seem worthy of study; however, previous studies appear to have been flawed or poorly designed. Berthold and associates conducted a randomized, double-blind trial to determine the effect of a garlic oil preparation on serum lipoprotein levels and cholesterol metabolism.

Patients were included in the study if they had not taken any medications to decrease serum lipid levels during the previous eight weeks and if their total cholesterol levels were between 240 and 348 mg per dL (6.22 and 9.01 mmol per L) and their triglyceride levels were less than 265 mg per dL (3.0 mmol per L). Patients remained eligible for the study if they took antihypertensive medication, thyroid hormones or hormone replacement medications. Twenty-five people were included in the study.

The patients were advised to follow their usual diets but were not allowed to take additional garlic or other food supplements during the study. They were randomized to receive either a placebo or 5 mg of garlic oil (equaling 4 or 5 g of fresh garlic cloves) per day. During the first four weeks of the study, all patients were given placebo. For the next 12 weeks, they received either the placebo or the garlic preparation. This regimen was followed by a four-week placebo washout period. The patients then entered a 12-week cross-over period. High-density lipoprotein and low-density lipoprotein cholesterol levels were calculated at the beginning and end of each phase.

The garlic preparation was well tolerated by all 25 patients included in the study, and no patients experienced adverse effects. Compliance was good for both the placebo and garlic preparations. The garlic preparation had no significant effect on lipoprotein fractions and no effect on parameters of cholesterol metabolism (including cholesterol absorption and cholesterol synthesis).

The authors conclude that the evidence does not support use of garlic oil products to lower serum lipid levels.