Including both walnuts and fish products in the diet is required to reduce risks of coronary heart disease, says a new study funded by the California Walnut Commission.
According to findings published in the American Journal of Clinical Nutrition, a diet supplemented with walnuts led to reductions in cholesterol levels, while a fish diet led to reductions in blood levels of triglycerides.
“Including walnuts and fatty fish in a healthy diet lowered serum cholesterol and triglyceride concentrations, respectively, which affects coronary heart disease risk favourably,” wrote the authors, led by Sujatha Rajaram from Loma Linda University in California.
It is estimated coronary heart disease (CHD) costs the British public health system more than €5bn per year.
According to the Department of Health, 18 per cent of men and 22 per cent of women had raised cholesterol levels in 1998.
The main cause of CHD is atherosclerosis, which is the build-up of fatty deposits on artery walls.
Rajaram and her co-workers recruited 25 adults with normal to mild hyperlipidaemia and randomly assigned them to a control diet containing no nuts or fish, a walnut diet providing 42.5 g walnuts per 10 mJ of energy, or a fish diet providing 113 grams of salmon twice a week. The feeding trials lasted for four weeks each and all the participants crossed over to the others. The diets provided the same energetic value.
The researchers report in the AJCN that consumption of the walnut diet led to reductions in both total and LDL cholesterol levels of 4.87 and 2.77 mmol/L, respectively, compared to the control diet (5.14 and 3.06 mmol/L, respectively). No such reductions were observed in the fish group, with total and LDL cholesterol levels of 5.33 and 3.2 mmol/L, respectively.
On the other hand, consumption of the fish diet led to decreased blood levels of triglyceride of 1.0 mmol/L, compared to 1.12 and 1.11 mmol/L for the control and walnut diets, respectively. HDL-cholesterol levels also increased following the fish diet to 1.23 mmol/L, compared to 1.19 and 1.18 mmol/L for the control and walnut diets, respectively.
Moreover, the ratio of total cholesterol to HDL cholesterol, reported to be the most specific lipid risk factor for cardiovascular disease (CVD), was lower in the walnut group, compared to the fish and control diets, said the researchers.
Nut science in a nutshell
The findings of the walnut diet are in agreement with previous findings from North American researchers. Researchers from Pennsylvania State University and the University of Guelph reported last year that incorporating more nut and nut-containing foods into the diet at the expense of foods full of saturated fats could reduce cholesterol levels by six per cent.
According to their study with macadamia nuts, the ratio of total cholesterol to HDL cholesterol decreased by 0.29 after consuming a macadamia-rich diet for five weeks.
The study was published in the Journal of Nutrition (Volume 138, Pages 761-767).
Source: American Journal of Clinical Nutrition
May 2009, Volume 89, Number 5, Pages 1657S-1663S, doi:10.3945/ajcn.2009.26736S
"Walnuts and fatty fish influence different serum lipid fractions in normal to mildly hyperlipidemic individuals: a randomized controlled study"
Authors: S. Rajaram, E.H. Haddad, A. Mejia, J. Sabaté