"A reduced-calorie diet containing unsaturated fats, such as those found in walnuts and olive oil, has similar effects on weight loss as a low-fat, higher-carbohydrate diet. However, a walnut-rich higher fat-diet has the most beneficial effects on the cholesterol-rich lipoproteins that are associated with increased risk for cardiovascular disease," Dr Cheryl Rock from the University of California stated.
The study published in the Journal of the American Heart Association saw just over 200 overweight and obese women with a body mass index between 27 and 40 randomly assigned to one of three study groups: a lower fat (20% energy), higher carbohydrate (65% energy) diet; a lower carbohydrate (45% energy), higher fat (35% energy) diet; or a walnut-rich, higher fat (35% energy), lower carbohydrate (45% energy) diet.
In a nutshell
Participants were given a detailed diet to follow which aimed for a 500-1000 kcal deficit per day. Saturated fat was limited in all groups and monounsaturated fat was increased in the higher fat group. Women in the walnut group consumed 45 g walnuts per day and all participants were encouraged to do an hour's moderate exercise per day.
Triglycerides, total cholesterol and high and low density lipoprotein cholesterol (HDL and LDL) were assessed by blood samples at baseline and six months.
Triglycerides decreased in all groups. The walnut-rich diet increased HDL, and reduced LDL in insulin sensitive women. The lower fat diet reduced total cholesterol and HDL in insulin sensitive women.
Weight loss was similar in all groups at an average 7.5% of initial weight, but the insulin sensitive women lost more weight with the lower fat compared to the lower carbohydrate diet (8.3% compared to 5.4%).
'There's something to be said for eating a handful of walnuts a day'
Previous research has suggested that regular consumption of nuts is associated with a reduced risk of cardiovascular disease. Walnuts contain polyunsaturated fatty acids and bioactive constituents and have been observed to be anti-inflammatory and anti-oxidant.
"Considering the results of this study, as well as previous walnut research on heart health and weight, there's something to be said for eating a handful of walnuts a day," Dr Rock said in a release
The authors acknowledged the limitations of adherence to and self-reporting of diets in the study, and the lack of assessment of lipoprotein particle size, known to be associated with cardiovascular risk and responsive to dietary intervention.
In future they also hope to explore the effect of walnuts on satiety, a critical factor in weight loss.