Being obese is known to be associated with increased health problems. These include diabetes, heart diseases, sleep apnoea and joint problems to name a few. It is also known that obese women have an increased risk of breast cancer. Is this association true for other cancers too?

Researchers from several universities from both sides of the Atlantic analysed the pooled data from the National Cancer Institute Pancreatic Cancer Cohort Consortium (PanScan) to look at possible association between obesity and risk of pancreatic cancer. The study included 2170 cases of pancreatic cancer and 2209 controls (Arch Intern Med 2010; 170: 791 – 802). They recorded body mass index (BMI) [< 18.5 underweight, 18.5 – 24.9 normal weight, 25.0 – 29.9 overweight, 30.0 – 34.9 obese and 35.0 severely obese], waist circumference and waist to hip ratio. In men, the risk of pancreatic cancer in those with the highest quartile of BMI is increased by 33% as compared to those with the lowest quartile BMI. In women the increased risk is 34%. An increased waist to hip ratio, between the highest and lowest quartile, was also associated with an 87% increased risk of pancreatic cancer in women.

We have two types of cholesterol in our body: ‘good’ cholesterol, namely high-density lipoprotein cholesterol (HDL-C), and ‘bad’ cholesterol called low-density lipoprotein cholesterol (LDL-C). We know that people with adequate levels of HDL-C are protected from heart disease. Does having more good cholesterol also protect you from cancer?

Researchers from Tufts University in Boston, USA, examined the relationship between HDL-C levels and the risk of developing cancer in 24 large randomised controlled trials (RCTs) of lipid-altering interventions (J Am Coll Cardiol 2010; 55: 2846 – 2854). The study found that there was a significant inverse association between baseline HDL-C levels and the rate of incident cancer. In other words, the higher the HDL-C level, the lower is the risk of cancer. After controlling for variables such as LDL-C level, age, BMI, sex and smoking status, the study found that for every 10 mg/dL increase in HDL-cholesterol, there is a 36% lower risk of developing cancer.

Most individuals put on weight because they eat more than they need. Whether you manage to lose weight or not depends on your motivation and determination. Participants in the reality show ‘The Biggest Loser’ manage to lose significant amounts of weight because they are being motivated to do so. Not everyone will get the chance to go on the show in order to be motivated. However, is the knowledge that becoming obese will increase your risk of developing cancer not enough to motivate you to keep trim?

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.