A recent study found that a tomato-rich diet may help reduce risk in postmenopausal women who are at an above-normal risk for breast cancer due to being overweight.
The researchers discovered that a certain nutrient found in tomatoes helped the body better regulate the breakdown of fat and sugar.
"Discuss your diet with a doctor."
The lead author of this study was Adana A.M. Llanos, PhD, MPH, from the Ohio State University Comprehensive Cancer Center in Columbus, Ohio; the School of Public Health at Rutgers University in Piscataway, New Jersey; and the Rutgers Cancer Institute of New Jersey in Brunswick, New Jersey.
The study included 70 postmenopausal women who were at heightened risk for breast cancer due to having either a significantly high body mass index (height to weight ratio) and/or an immediate family member who had breast cancer.
The body mass index (BMI) range that constitutes a heightened risk of breast cancer is 25.0 to 42.0 kg/m2. The average BMI of the participants was 30.0 kg/m2.
A person is considered obese if they have a BMI of 30.0 kg/m2 or higher. Forty-three percent of the participants were obese.
About 81 percent of the participants were white and the average age was 57.2 years old. None of the participants were taking hormone replacement therapy.
The study period was from February 2003 through September 2004.
The researchers had each participant go through a 26-week program that included a soy diet and a tomato diet.
The program had three different 'washout' periods when the participants had to stop eating tomato and soy products for two weeks at a time; these periods happened at the beginning, the midpoint and the end of the program. Between these washout periods, there were two 10-week dietary interventions.
During the first 10-week intervention, the researchers told the participants to eat two or more tomato products per day and to abstain from soy products. Tomatoes have lycopene — a naturally occurring chemical that can potentially reduce the risk of heart disease and breast cancer.
The second 10-week intervention involved the participants abstaining from tomato products and eating at least 40 grams of soy protein per day.
The researchers took blood samples and weight measurements at the beginning of the 26-week program, and after each of the 10-week interventions.
Adiponectin and leptin are two hormones that help regulate the breakdown and storage of sugars and fats. Overweight and obese people typically have high levels of leptin and low levels of adiponectin.
Previous studies have suggested that breast cancer risk decreases if adiponectin increases (i.e., they have an inverse relationship). It has also been suggested that risk of breast cancer and leptin have a positive association —that is, breast cancer risk may increase as leptin increases, and vice versa.
Dr. Llanos and colleagues measured the levels of each of these hormones after each diet to see if either or both of the diets could help the participants lower their risk of breast cancer.
No significant changes were found in body weight, waist size or BMI after either diet.
The findings showed that in the study population as a whole, adiponectin levels increased by 9 percent after the tomato diet. In just the non-obese participants, there was a 13 percent increase of adiponectin.
The researchers also found that leptin levels fell by 11 percent overall, and by 24 percent in the non-obese participants.
Following the soy diet, the findings showed a 9 percent reduction in adiponectin in the study population as a whole and an 11 percent reduction among the non-obese participants.
In addition, there was an 8 percent decrease in leptin for the overall participant population after the soy diet, and an 18 percent reduction in the non-obese participants.
The only statistically significant changes were the increases in adiponectin after the tomato diet.
These findings suggested that eating tomato-based foods may help reduce the risk of breast cancer by helping reduce the risk of obesity in postmenopausal women with high BMIs.
These researchers believe that more studies are needed to confirm the relationship between the lycopene in tomatoes, and the relationship with weight-related hormones and breast cancer risk.
The authors mentioned a few limitations of their study. First, every participant completed the diets in the same order (tomato first, then soy). Second, the findings are only applicable to postmenopausal women who are at increased risk for breast cancer. Third, the researchers only considered tomato and soy dietary information. Fourth, tomatoes have many nutrients in them and the study's focus was just on lycopene.
This study was published on December 18 in The Journal of Clinical Endocrinology & Metabolism.
The Breast Cancer Research Foundation and Ohio State University provided funding.