Confused again?

Academics from the Harvard University recently published a meta-analysis and review of the available studies on the effects of walnut consumption on blood lipids and other cardiovascular risk factors (Am J Clin Nutr 2009; 90: 56 – 63). They analysed the results from 13 studies involving 365 subjects. The diets lasted 4 – 24 weeks with walnuts providing 10 – 24% of total calories. The study showed that walnuts supplemented diets, compared to control diets, resulted in a significantly greater decrease in total cholesterol and LDL-cholesterol concentrations. (LDL-cholesterol is normally referred to as the ‘bad’ cholesterol.) If larger and longer-term trials confirm these findings and show beneficial cardiovascular effects, then everyone would most likely want to have a high-walnut-enriched diet.

No doubt some people would embark on this walnut-enriched diet after reading just the article above. However if one then reads the article in GUT on linoleic acid and ulcerative colitis (GUT 2009; epub 23^rd July) one might hesitate to start the diet. (Sunflower, corn, wheat germ, soybean and walnuts oils are a rich source of linoleic acid. Linoleic acid is an unsaturated omega-6 fatty acid used in the synthesis of arachidonic acid which is a component of the cell membrane. Metabolites of arachidonic acid have pro-inflammatory properties and are increased in the mucosa of patients with ulcerative colitis (UC). UC is a condition where the lining of the colon suffers from chronic inflammation.) Researchers from the University of East Anglia analysed the dietary data from 203,193 men and women aged 30 – 74 years, resident in the UK, Sweden, Denmark, Germany and Italy and participating in the prospective cohort European Prospective Investigation into Caner and Nutrition (EPIC) study. They were followed up for a median of 4 years and 126 participants developed UC. The risk of developing UC among participants who had the highest quartile of linoleic acid intake was increased by 149%.

On the one hand we read that walnut enriched diet lowers total cholesterol and LDL-cholesterol concentrations in the body. On the other hand too much linoleic acid (walnuts oil is rich in linoleic acid) in the diet increases the risk of developing UC. Feeling frustrated and confused?

Until we can get clear and definitive data, it is difficult to be adamant on what food stuff you must eat and in what quantity. In the meantime, I myself would stick to the principles of eat healthily, eat in moderation and take regular exercise.