Two studies demonstrated the dangers of a diet that includes high levels of fat and processed foods.
A major European study shows that women with raised levels of blood sugar face significant extra risks of suffering cancers of the pancreas, skin, womb and urinary tract.
And older women with the fattiest diets have a 15% increase in their chances of developing breast cancer, according to a U.S. study.
It found fat intake levels of 40% of diet put women most at risk. Levels rated as "high" in the study were close to the British average of 38%.
High blood sugar levels are linked to unhealthy diets, including fatty and processed foods, and can lead to Type 2 diabetes.
Previous research has shown an increased risk of cancer in patients with this form of diabetes, which usually occurs in middle age.
But the new findings demonstrate that rising blood sugar levels also increase the cancer risk in women.
It shows that the 25% of women with the highest blood sugar readings had a 26% greater chance of developing cancer than those with readings in the bottom quarter bracket.
For women before the menopause with high blood sugar, there was also an increase in breast cancer risk.
Almost 65,000 adults took part in the 13-year study, but no link was found in men. Researchers identified 2,478 cases of cancer.
The scientists, led by Dr Par Stattin, from Umea University Hospital in Sweden, also observed a general increase in blood sugar levels.
Raised blood sugar levels in men appeared to protect against prostate cancer, though not to a significant degree.
The research was partly paid for by the World Cancer Research Fund.
Dr Greg Martin, science and research manager for WCRF UK, said, "The results of this research are concerning. However, the good news is that it is possible to reduce your blood sugar levels by eating a healthy balanced diet with lots of fruit and vegetables and maintaining a healthy weight.
"We know that up to 40% of cancer cases can be prevented by this type of healthy lifestyle, so this is just another reason for people to make those small changes that could make a big difference."
Natasha Marsland, care manager at Diabetes UK said, "This is an interesting study. However, much more research needs to be done before we can conclude if there is a link between high blood glucose levels and cancer."
U.S. researchers at the National Cancer Institute in Bethesda, Maryland, found that post-menopausal women who eat a high-fat diet may be at greater risk of breast cancer.
They questioned 188,000 postmenopausal women about how often they ate certain foods how much of the foods they consumed to determine how fat intake affects breast cancer risk.
Of the women surveyed, 3,500 developed invasive breast cancer, according to the study, which is published in the Journal of the National Cancer Institute.
The researchers found that doubling fat intake, from 20% to 40%, was associated with a 15% rise in breast cancer risk.
The increase was similar for all types of fat -- saturated, monounsaturated and polyunsaturated.
Dr Anne Thiebaut, who led the researchers, said, "We detected a direct association between fat intake and the risk of invasive breast cancer."
Scientists have still to establish how fat in the diet promotes breast cancer.
But it may work by leading to greater body stores of fat which in turn produce higher circulating levels of the hormone oestrogen. This is known to trigger breast tumours.
Dr Emma Pennery, nurse consultant at Breast Cancer Care, said, "Whilst this research adds to existing evidence in this area, other studies have not reached the same conclusions so we are still some way off understanding the exact influence of a high fat diet.
" However, a high fat diet can lead to weight gain and it is widely accepted that being overweight, particularly after the menopause, increases the risk of breast cancer."
Britain has already been identified as the junk food capital of Europe ñ with the worst obesity problem.
Teenagers eat 60% more confectionery than youngsters in Holland and France, who rank second in a table of junk food eating habits from analysts Datamonitor. They consume more than three times the amount that Italian children do.
The problems continue in adult life. EU figures show adult Britons are Europe's fattest. British women head the league table, with 23% clinically obese. Men fare little better, with 22.3% classified as obese ñ behind only Malta.
From the March 26, 2007, Prepared Foods e-Flash