AICR's Cancer Research Update

Issue 43 — May 19, 2010

Also in this issue:

  1. Body Shape, Weight, and Pancreatic Cancer
  2. Adult Weight Gain May Increase Breast Cancer Risk
  3. Read Food Labels: Eat Healthier
  4. In Brief: How Many Antioxidants Are in There?
Margot P. Cleary

Scientist in the Spotlight: Margot P. Cleary

Finding Fat's Role in Cancer

Margot P. Cleary, PhD, a nutritional biochemist at the University of Minnesota’s Hormel Institute, was one of the first scientists to show that leptin, a hormone produced by adipocytes, may stimulate the growth of breast cancer cells. Today, leptin’s role in cancer is a key area of research. Funded by AICR for a study on obesity and prostate cancer, Dr. Cleary has conducted numerous lab studies that may help explain how excess fat tissue leads to cancer development.

Q: You started in obesity research; how did you shift into the obesity-cancer field?

A: In the 1990s there wasn’t a lot of obesity research at the Hormel Institute. I had been working in adipose tissue development. I was working a lot with genetically obese rats and diet-induced obesity, looking at different interventions and how it affected the development of obesity. Then I took some maternity leave and after that, I wanted to recharge myself. I became aware of the literature on the potential role of obesity in breast cancer. I thought this might be a new avenue to use my background in adipose tissue.

Q: What led you to start looking at leptin’s role in cancer?

"For leptin, we still haven’t made a direct link between serum levels of leptin and tumor development…. We’re still in a phase of trying to figure it out."

A: I ended up going to Mayo Clinic on a sabbatical and we wanted to look at the effects of obesity and food restriction on cancer in mice. Now it’s getting to be the late 1990s and leptin had been identified. So we crossbred obese, leptin-deficient mice with mice that develop mammary tumors, and they didn’t get any tumors. This started us scratching our heads. It was the total opposite of what we had anticipated. As this was going on there was more and more information on leptin and leptin receptors. They were finding leptin receptors in tissues all over the body and then in some cancers.

Q: How did you follow-up?

A: We did a breast cancer cell study and found that if you added leptin it increased cell proliferation. Our animal study made sense now. Leptin could be a growth factor because it tied back into obesity. Obese women have higher leptin levels.

Q: Does that mean there is a definite link?

Leptin Molecule

Leptin was discovered in 1994, named
from the Greek word leptos, meaning thin.

A: Well, after that I got funded to do an animal study and we looked at dietary induced obesity and breast cancer. We saw that the mice that gained the most weight developed tumors earlier. For leptin, we still haven’t made a direct link between serum levels of leptin and tumor development. There are some studies to suggest leptin is involved and others to say it’s not. We’re still in a phase of trying to figure it out.

Q: Is that what you’re working on now?

A: Now we’re refining this theory: it might not be the levels of leptin, but it could be the ratio of leptin and a second protein called adiponectin. As obesity increases, leptin goes up and adiponectin goes down. The ratio of these adipokines may be more important in breast cancer than their absolute concentrations.

With your gernerous support, AICR funds reserach in diet, physical activity and weight management. Please donate now.Q: What do you hope to do next?

A: In breast cancer, we’ve been looking at calorie restriction and cancer prevention. We haven’t yet looked at the obesity aspect of the adiponectin: leptin ratio. Are there ways you can alter this ratio? We know you can do this by calorie restriction and we know calorie restriction lowers cancer risk. I want to find out what the mechanisms are and if you can alter the ratio by other means [than calorie restriction]. If you can modulate the levels by dietary intervention and weight loss and it’s associated with decreased mammary tumors, we will then have more of a rationale to push harder for lifestyle interventions.

Excerpted from ScienceNow.

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Chocolate SquaresIn Brief

How Many Antioxidants Are in There?

Nutrition researchers now have a new tool to better understands how foods may influence cancer and other disease: a database. A new database containing the antioxidant content of more than 3,100 foods, beverages, spices, and herbs used around the world is now available, according to a study published in Nutrition Journal. It is the most comprehensive antioxidant database ever published, according to the study authors.

Not surprising, the database shows that plant-based foods contain significantly more antioxidants than non-plant foods. But the results showed large variations both between as well as within each food category. For example, in the chocolate category, antioxidant content ranged from 0.23 mmol/100 g in white chocolate to 14.98 mmol/100 g in one dark chocolate sample.

See the study in Nutrition Journal for the full antioxidant food table.

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Research Roundup

Woman Shape with superimposed Pear Shape.jpgBody Shape, Weight, and Pancreatic Cancer

A new study supports previous findings that being overweight – and especially having that weight around your abdomen – increases the risk for pancreatic cancer. The study, published this week in the Archives of Internal Medicine, supports the findings of AICR’s 2007 expert report.

The current study used pooled data from the National Cancer Institute Pancreatic Cancer Cohort Consortium (PanScan) on approximately 4,400 individuals, about half with pancreatic cancer and half free of the disease. For all participants, risk for pancreatic cancer climbed as BMI increased. Overall, those with the highest BMI were at 33 percent higher risk of pancreatic cancer than those with the lowest BMI. For women, having a large waist and a large waist in relation to one's hips – waist to hip circumference (WHR) – was most strongly linked to increased risk of pancreatic cancer.

AICR’s expert report found excess body fat (convincingly) and abdominal fat (probably) causes pancreatic cancer.

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Adult Weight Gain May Increase Breast Cancer Risk

Fat Woman On ScaleThe all-too-common increases in weight among adults may lead to a substantially higher risk of postmenopausal breast cancer, according to results of a study presented at a major cancer conference last month. Excess body fat is linked with increased risk of postmenopausal breast cancer, yet this is one of the relatively few studies that has focused on the timing of weight gain and breast cancer risk.

In this study, researchers analyzed self-reported data from approximately 72,000 women who were 55 to 74 years old at study entry. Women who reported a BMI increase of 5 units (kg/m2) or more between age 20 and 50 were at an 88 percent increased risk of developing postmenopausal breast cancer, compared with women who reported a stable BMI, whether the BMI was relatively high or low. BMI gain both before and after age 50 independently contribute to increased risk of postmenopausal breast cancer.

Results showed that over half of the study population's BMI increased 5 kg/m2 or more between age 20 and study entry. A BMI increase of 5 kg/m2 is equivalent to a woman of average height, 5'4", gaining approximately 30 pounds.

Study presented at the American Association for Cancer Research 101st Annual Meeting 2010, Washington, DC.

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Nutrition Facts LabelRead Food Labels: Eat Healthier

When doctors advise ill patients to eat healthier, they are significantly more likely to read food labels and actually eat healthier than patients not so advised, according to a study published in the April issue of the Journal of the American Dietetic Association.

The study included approximately 3,800 individuals and focused on those who had at least one chronic condition, such as type 2 diabetes. Participants recalled if their health practitioner had advised them to reduce dietary fat or calories, how frequently they used the Nutrition Facts label, and foods they ate recently.

Overall, individuals with a chronic disorder read food labels more frequently than patients free of disease. Among patients with a chronic disease, the odds of reading food labels when advised to do by their health professional was 50 percent higher compared to patients not given such advice. Women were more than three times more likely to read food labels than men. Those who read food labels consumed less energy, saturated fat, carbohydrates, and sugar, and more fiber than those who did not read labels.

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