DIET, OBESITY AND LOW PHYSICAL-ACTIVITY

In the early 1980s, Doll and Peto estimated that about 35% of all deat hs from cancer in the United States were attributable to dietary facto rs, with a margin of uncertainty ranging from 10 to 70%. Since then, s everal dietary factors, e.g. fat and meat, have been suggested to incr ease the risk for cancer, while other factors, e.g. fibre, fruit and v egetables, have been suggested to decrease the risk. The case-control and cohort studies have, however, given ambiguous results, and the ove rall evidence is far from conclusive. The major findings on dietary fa ctors that increase risk have been reported from case-control studies, but have not been confirmed in large population-based cohort studies. Although the research in this area Indicates that diet is important i n cancer prevention, current knowledge does not allow reliable estimat es of the numbers and proportions of cancers that could be avoided thr ough well-described modifications of dietary habits. During the last 1 0 years. low physical activity has been pinpointed as a risk factor fo r cancers at various sites, especially the colon; however, the causal mechanism is still unknown. Obesity, defined as a body mass index of 3 0 or more, is consistently associated with endometrial and gall-bladde r cancers in women and renal-cell cancer in both men and women. As the prevalence of obesity was between 5 and almost 20% in the Nordic popu lations in 1995, 625 cancer cases (310 endometrial cancers, 270 renal- cell cancers in men and women and 45 gall-bladder and bile-duct cancer s among women) can be predicted in the Nordic countries around the yea r 2000 to be caused by obesity. This implies that about 1% of all canc ers in Nordic women and less than 1% of those in Nordic men could be a voided around the year 2000 if a healthy body weight could be maintain ed by all inhabitants.