The new studies both link dietary patterns with increased cancer risk - with the first suggesting that eating a high-fat diet beginning at puberty speeds up the development of breast cancer and may actually increase the risk of cancer similar to a type often found in younger adult women.
Writing in Breast Cancer Research, the findings suggested that in addition to accelerated breast cancer development, a high-fat diet produces a distinct gene signature in the tumours which is consistent with a subset of breast cancers - known as basal-like - that can carry a worse prognosis.
"This is very significant because even though the cancers arise from random mutations, the gene signature indicating a basal-like breast cancer shows the overarching and potent influence this type of diet has in the breast," explained Professor Sandra Haslam of Michigan State University - who led the project. "Cancers of this type are more aggressive in nature and typically occur in younger women."
"It's important to note that since our experimental model did not involve any weight gain from the high-fat diet, these findings are relevant to a much broader segment of the population than just those who are overweight," said Richard Schwartz, a co-author of the paper. "This shows the culprit is the fat itself rather than weight gain."
Schwartz noted that early evidence has suggested that fat, which in this case was saturated animal fat, could potentially have permanent effects even if a low-fat diet is introduced later in life. He cautioned, however, that this preliminary finding requires further investigation and doesn't indicate with certainty that humans will be affected in the same way.
"Overall, our current research indicates that avoiding excessive dietary fat of this type may help lower one's risk of breast cancer down the road," he said. "And since there isn't any evidence suggesting that avoiding this type of diet is harmful, it just makes sense to do it."
Further research, published in Science, has suggested that high cholesterol may also be linked to breast cancer development - revealing that a by-product of cholesterol functions like the hormone oestrogen to fuel the growth and spread of the most common types of breast cancers.
Led by researchers at the Duke Cancer Institute report, the researcher team used mouse models and tumour cell lines to investigate the link between cholesterol and cancer development after previous work suggested a strong link - especially in post-menopausal women.
"A lot of studies have shown a connection between obesity and breast cancer, and specifically that elevated cholesterol is associated with breast cancer risk, but no mechanism has been identified," explained senior author Dr Donald McDonnell. "What we have now found is a molecule – not cholesterol itself, but an abundant metabolite of cholesterol – called 27HC that mimics the hormone oestrogen and can independently drive the growth of breast cancer."
The team suggested that dietary changes or therapies to reduce cholesterol may also offer a simple, accessible way to reduce breast cancer risk.
Full access to the cholesterol paper published in Science can be found here
Full access to the high-fat diet paper published in Breast Cancer Research can be found here