A recent study published in BMJ Open Diabetes Research & Care sings the praises of a daily diet that includes walnuts. Should we all increase our intake of Waldorf salad?
Walnuts have long been considered to convey a wide range of benefits, but adequate studies on the majority of these claims are yet to appear.
However, a recent trial has set out to study the implications of a walnut-rich diet on a number of health factors including cholesterol levels, overall weight and quality of diet.
The study concluded that eating walnuts daily leads to an improvement in blood vessel wall (epithelial) function and a lowered cholesterol level.
The trials also showed little or no effect of walnuts on a number of other parameters including blood pressure.
The wonderful walnut
The walnut, although technically not a nut, has been heralded as a healthy food item by many nutritionists. Walnuts are a dense and fatty foodstuff, comprising around 15% protein and an impressive 65% fat.
Previous studies have inferred walnut's ability to slow prostate cancer, reduce cholesterol and insulin sensitivity, and lower levels of IGF-1 (implicated in prostate and breast cancer). Others have claimed that walnuts reduce blood pressure, oxidative stress and inflammatory markers.
Although some of the claims are more spurious than others, the current study - carried out by Dr. David Katz at Yale University Prevention Research Center, Griffin Hospital, in Connecticut - aimed to investigate some of the health claims in a little more detail.
The trial used 112 individuals: 31 men and 81 women, aged 25-75, all with a relatively high risk of developing diabetes. The participants were split into two groups. One group received counseling to achieve a lower calorie diet, the other group did not.
Within each of the groups, individuals were randomly split again into a further two subgroups. The first subgroup consumed 56 g of walnuts per day, the other completely abstained from walnuts for 6 months. After a 3-month break, the intervention arms were reversed.
At the start of the trial, and at the 3, 6, 12 and 15-month mark, the participants were assessed for a wide number of markers.
The markers were as follows: dietary intake, weight, height, body mass index (BMI), waist circumference, blood pressure, fasting blood glucose (glucose measured after 8 hours of fasting), cholesterol and HbA1c (glycated haemoglobin - this marker gives an indication of average glucose levels over prolonged periods).
Did the walnuts weave their wonder?
After controlling for factors such as age, amount of regular exercise taken and their intake of calories and fat, the study authors concluded that the walnuts were associated with improved quality of diet.
Importantly, the study appears to show an improved epithelial functioning in the participants who consumed the walnuts. The researchers also found a reduction in LDL (bad) cholesterol.
These positive effects were found to be independent of whether caloric intake was controlled or not.
On the other hand, maybe unsurprisingly given their caloric levels, those on uncontrolled diets who ate walnuts daily saw an increase in total body fat. However, when combined with a calorically restricted diet, their waist circumference decreased significantly.
The addition of walnuts to the participants' diets was found to have no significant effect on blood pressure, blood glucose or HDL (good) cholesterol; HbA1c was seen to increase in both types of diet, regardless of dietary counseling.
The researchers conclude:
"Our data suggest that inclusion of walnuts in the diet, with or without dietary counseling to adjust caloric intake, improved diet quality and may also improve [endothelial function], and reduce total and LDL cholesterol in this sample of adults at risk for diabetes."
It should be noted that the study was funded by the California Walnut Commission, and the researchers say that further studies need to be conducted before any solid conclusions can be drawn. Research using a wider variety of individuals will be necessary to paint the full picture.
Medical News Today recently covered research that concluded eating peanuts daily could lower death risk from cancer and other diseases.