Each year 6,700 people in Britain are diagnosed with kidney cancer, most over 65 and more men than women. It is the UK's 13th most common cause of cancer and is notoriously difficult to treat. Swedish and American scientists studied 140,057 women aged between 50 and 79 for almost eight years, and found that yo-yo dieting and a large waistline were far bigger risk factors in the development of the disease in older women than just obesity.
Women whose weight fluctuated by more than 4.5kg (10lb) on more than ten occasions during their adult life were two and a half times more likely to develop kidney cancer than women whose weight had remained stable. The researchers also found it was safer for women to gain weight steadily as they grew older than to lose weight and keep it that way through strict dieting. Women who did this were found to have a 60 per cent increased risk of developing the cancer.
Obesity was an important factor in kidney disease risk. The scientists report in the American Journal of Epidemiology that when they measured waistline as a proportion of hip size, they found the greater the ratio between waist and hips, the more chance a woman had of getting the disease. When compared to average waist size, those with the largest waist to hip ratios were found to have an 80 per cent increased risk of developing a type of kidney cancer known as renal cell carcinoma (RCC). In the study, the authors say there could be several explanations to why repeated weight changes and large waistlines are such risk factors for women. They point out that studies have shown that weight cycling is associated with increased incidence of high blood pressure, another risk factor for RCC.
Another possibility is that frequent weight fluctuations may result in kidney damage by inducing metabolic or functional changes that increase susceptibility to cancer. Colin Waine said: "When we think of obesity we tend to think of the risks of diabetes and heart disease but the risks are not inconsiderable for certain cancers. The most prominent ones are post-menopausal breast cancer and colonic cancer, but others such as pancreatic, kidney and oesophageal cancer are affected too. Yo-yo dieting is never a healthy thing to do because the body never gets a chance to settle. It knocks the metabolism all to hell, which is bad for you in many ways."
Earlier this year, the world's largest study of weight loss concluded that diets are damaging for most slimmers because of the tendency to regain the weight. More than two-thirds pile the pounds straight back on, raising the danger of heart attack, stroke and diabetes, said University of California researchers.
