Published: May 21, 2014 By Charles Bankhead, Staff Writer, MedPage Today

ORLANDO — A diet rich in complex carbohydrates and fiber had a significant favorable association with prostate cancer risk, analysis of veterans’ medical records showed.

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Patients with the highest carbohydrate intake had a 70% lower risk of prostate cancer as compared with patients who consumed the least amount of carbohydrate-based food. The benefits applied to blacks and whites and to the risk of low-grade and high-grade prostate cancer.

High fiber intake was associated with a significant reduction in the risk of high-grade prostate cancer, as reported here at the American Urological Association meeting.

“Among men consuming a Western diet, higher carbohydrate intake reduced the risk of prostate cancer, overall and both low- and high-grade prostate cancer,” said Adriana Vidal, PhD, of Duke University. “This was true in both black and white men.

“High fiber intake reduced the risk of high-grade, and we found that intake of foods with a high glycemic index might increase the risk of prostate cancer in black men.”

Studies of dairy intake and metabolic syndrome produced mixed results regarding relationships to prostate cancer risk.

Vidal pointed out that a high-carbohydrate diet has been hypothesized as a risk factor for prostate cancer, mediated by an alteration in the insulin/insulin-like growth factor-1 (IGF-1) axis. IGF-1 inhibits apoptosis and promotes cellular proliferation and differentiation, characteristics closely associated with tumorigenesis.

Some evidence suggests that the IGF-1 axis varies by race. In particular, black and white men have similar levels of IGF-1, but blacks have less IGF binding protein-3, one of several molecules that modulate IGF-1 activity, resulting in higher levels of free IGF-1. Blacks also have an increased rate of carbohydrate oxidation.

On the basis of these observations, Vidal and colleagues hypothesized that increasing carbohydrate intake is associated with an increased risk of prostate cancer and that the association would be stronger in black men.

Investigators evaluated data from an ongoing study at the Durham Veterans Affairs Medical Center. The analysis comprised 156 men with biopsy-proven prostate cancer and 274 without prostate cancer.

Study participants completed a validated food-frequency questionnaire. Statistical associations were adjusted for age, race, body mass index, and caloric intake.

The overall analysis of carbohydrate intake showed a numerical difference in carbohydrate intake but in the opposite direction of the hypothesis. The men without prostate cancer had higher self-reported daily carbohydrate intake (mean 224 versus 204 g/day, P=0.069).

Stratification of the day into tertiles of carbohydrate intake transformed the numerical difference into statistically significant differences. Analysis of all 430 men included in the study showed that men in the second tertile of carbohydrate consumption had a 71% lower risk of prostate cancer as compared with men in the lowest tertile (P=0.001). The association was similar in white (odds ratio 0.33, P=0.009) and black (OR 0.36, P=0.028) men.

Men in the top carbohydrate intake tertile had a 64% reduction in prostate cancer risk (P=0.007), but analysis by race showed that the association persisted only among black men (OR 0.12, P=0.007).

Further analysis of carbohydrate consumption and prostate cancer showed that men in the two highest categories of carbohydrate intake had significant protection from both low- and high-grade prostate cancer, in the range of 60% to 70% for the second tertile and almost 75% in the third tertile (P=0.027 to P=0.003).

Analysis of glycemic index did not yield any significant associations, although black men with a high-glycemic diet appeared to have an increased risk of prostate cancer (OR 2.09, P=0.060).

Men with the highest fiber intake had a 50% lower risk of prostate cancer in the overall analysis (OR 0.49, P=0.047), but the association did not persist in the analysis by race. Examination of low- and high-grade prostate cancer showed that the benefit pertained only to the latter (OR 0.34, P=0.019).

Another study reported during the same session showed an inconsistent association between metabolic syndrome and prostate cancer. The study included 6,426 men from the REDUCE trial of prostate cancer chemoprevention with dutasteride (Avodart).

Metabolic syndrome comprises five high-risk characteristics: abdominal obesity (reflected in high waist circumference), hypertension, elevated triglycerides, low HDL cholesterol, and elevated fasting glucose. The presence of three or more risk factors meets diagnostic criteria for the syndrome.

Analysis of the REDUCE data showed that 2,171 men had one component of metabolic syndrome, 724 had two, and 163 had three or four components. During follow-up in the trial, 1,447 men developed prostate cancer, reported Katharine N. Sourbeer, BS, of the Institute for Medical Research, in Durham, N.C.

Multivariable analysis showed that men with one metabolic syndrome risk factor had a lower risk of prostate cancer (OR 0.87, P=0.041), but the presence of two, three, or four risk factors had no association with prostate cancer risk.

Examination of metabolic syndrome components by cancer grade showed no associations with low-grade cancer. Men with two risk factors had an increased risk for high-grade prostate cancer that fell just shy of statistical significance (OR 1.35, P=0.059). The risk of high-grade prostate cancer was significantly increased in men who had three or four components of metabolic syndrome (OR 1.94, P=0.02).

Several studies have suggested that high calcium intake is associated with an increased risk of prostate cancer. Studies of calcium-rich dairy products have yielded inconclusive data regarding prostate cancer risk, said Raj Satkunasivam, MD, of the University of Southern California in Los Angeles.

To examine associations between dairy nutrients and prostate cancer, investigators analyzed data from the California Collaborative Prostate Cancer case-control study. The analysis included about 1,100 men with advanced prostate cancer and a matched control group of similar size including men without prostate cancer.

As compared with men who reported rarely or never drinking milk, low intake was associated with a 33% increase in the odds of advanced prostate cancer, increasing to 43% among men reporting high intake (P=0.037 for trend). However, analysis of calcium intake showed no significant associations with advanced prostate cancer.

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