Milk, cream and cheese can reduce the survival chances of women with breast cancer, a study has found.
Patients who consumed one or more serving of high-fat dairy products a day had a 64% greater risk of dying from any cause, said researchers.
They also had a 49% higher likelihood of death from breast cancer than women who avoided the foods.
High-fat dairy products in the study included whole milk, condensed or evaporated milk, cheese, yoghurt , cream, ice cream, and custard.
A total of 1,500 women with breast cancer were questioned about their diets and monitored for an average of 12 years.
Women were asked how often they consumed dairy foods during the previous year, what the portion sizes were, and which products were full fat, low fat or non-fat.
All had been diagnosed about two years before joining the study. During the follow-up period, 349 women had a recurrence of breast cancer, and 372 died, 189 from breast cancer.
Scientists suspect cow oestrogen in dairy products may underlie the findings, published in the Journal of the National Cancer Institute.
Previous studies have suggested a causal link between higher lifetime exposures to oestrogen and breast cancer. High fat dairy products are higher in oestrogen than low-fat products.
Lead researcher Candyce Kroenke, from the Kaiser Permanente research institute in the US, said: "Women consuming larger amounts of high-fat dairy had higher breast cancer mortality as well as higher all-cause mortality and higher non-breast cancer mortality.
"Specifically, women consuming one or more servings per day of high-fat dairy had a 64% higher risk of dying from any cause and a 49% increased risk of dying from their breast cancer during the follow-up period."
The research is part of the Life After Cancer Epidemiology (Lace) study looking at the impact of lifestyle on breast cancer survival and occurrence.
Dr Susan Kutner, chair of the Kaiser Permanente Northern California Regional Breast Care Task Force, said the findings lend weight to the importance of a low-fat diet.
"Women have been clamouring for this type of information," she said. "They're asking us, tell me what I should eat? With this information, we can be more specific about recommending low-fat dairy products."