Eating a diet high in animal fat leads to high saturated fat intake – the chief cause of high cholesterol. The liver already produces all the cholesterol it needs (roughly 1gm per day) to meet our needs. A high animal fat diet is dangerous particularly when there is also a lack of fiber and exercise in ones daily routine. Pathologies such as artherosclerosis (hardening of the arteries, due to fat lining the inside of veins and arteries, which then blocks oxygen to the heart, causing a portion of the heart to 'die'), heart attack, stroke, arthritis, inflammation and kidney failure may then develop.
A study published in 2003 in the Journal of the National Cancer Institute indicates that young women who eat more red meat and full-fat dairy products such as cheese may be raising their risk of breast cancer. When comparing the women in the highest fat intake group with women in lowest intake group, those with the highest intake had a 33% greater risk of invasive breast cancer according to Eunyoung Cho of Brigham and Women's Hospital and Harvard Medical School.
Breast cancer takes years to develop, usually showing up after menopause, and factors early in a woman's life may be important. This study is significant because it included women who had not yet reached menopause.
The study of more than 90,000 women aged 26 to 46 was taken from the Nurses' Health Study, in which volunteers answer regular questionnaires about diet and lifestyle and that data is analyzed by researchers who track the women's health. Over the eight years of the study, 714 of the women developed invasive breast cancer. A higher risk of breast cancer was observed among women who ate foods rich in animal fat such as red meat, cheese, ice cream and butter during their 20s, 30s and 40s.
Although it is not clear how animal fat may cause cancer, this study does indicate that there may be good reason for lowering overall animal fat intake, especially during a woman's early adult life.