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.

The levels of ascorbic acid (vitamin C), naringin and other phenolic acids were the same for both grapefruit types. The most concentrated phenolic acids were ferulic (about 27 mg per 100g) and sinapic (about 20 mg per 100g).

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.

Further in vitro study is clearly needed to identify the bioactive compound.

The research was welcomed by Cathy Ross from the British Heart Foundation (BHF) who said the study was futher support for the benefits of a diet rich in fruit and vegetables. Ross told NutraIngredients.com: "A diet rich in antioxidants is beneficial in reducing cholesterol levels and your risk of Coronary Heart Disease (CHD)."

Heart disease causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169 billion (£116 billion) per year.