Grapefruits and other citrus fruits are known to contain high concentrations of antioxidants like vitamin C, and polyphenols, especially flavonoids. The new study claims to be the first to look at different grapefruit types and their influence on humans who suffer from high blood cholesterol (hyperlipidemia) and hardening of the arteries (atherosclerosis), both of which play major roles in heart disease.

The in vitro studies measured antioxidant activity in terms of radical scavenging activity, beta-carotene linoleate models, and oxygen radical absorbance capacity (ORAC). Red peeled grapefruits scored 15 per cent higher on the beta-carotene test, and 10 per cent higher for radical scavenging.

For the human trial, 57 post-operative bypass patients with high triglyceride levels in the blood (hypertriglyceridemia) were divided into three groups. The standard anti-atherosclerosis diet of two groups was supplemented by one Israeli Jaffa red or white grapefruit for 30 days. The third group ate the standard diet and was considered the control group (CG).

The standard anti-atherosclerosis diet consisted of 66 per cent energy intake from carbs, 25 per cent from protein and 9 per cent from fat.

“The results of the investigation in humans have shown that a generally accepted antiatherosclerosis diet supplemented with fresh red or blond grapefruits positively influences the serum levels of total cholesterol and low-density lipoprotein [bad] cholesterol (LDL-C),” said lead researcher Shela Gorinstein.

“However, only a diet supplemented with red grapefruits was effective in significantly lowering the level of serum triglycerides,” said Gorinstein.

The scientists propose that the health benefits of the grapefruits are most likely due to the antioxidants present. However, the researchers could not explain the differences between the white - and red types.

“We cannot exclude that only red grapefruit cultivars contain some special bioactive compounds which are responsible for the triglyceride-lowering effect,” said Gorinstein.

Editor's Note: There are certain medications that may interact with grapefruit or grapefruit juice. Please check with your pharmacist or physician.

Source: Diabetes In Control: The results are published on-line in the Journal of Agricultural and Food Chemistry (doi:10.1021/jf058171g).