Diet and Exercise – Cancer Risk

From Medscape. 

December 18, 2006 — Consuming a low-protein, low-calorie diet for the long term or engaging in endurance training is linked with a decrease in cancer risk, according to the results of a study reported in the December issue of the American Journal of Clinical Nutrition.

“Western diets, obesity, and sedentary lifestyles are associated with increased cancer risk,” write Luigi Fontana, MD, PhD, from the Washington University School of Medicine in St. Louis, Missouri, and colleagues. “The mechanisms responsible for this increased risk, however, are not clear…. We hypothesized that lower protein and calorie intakes, greater physical activity, and lower adiposity would be associated with beneficial effects on the plasma growth factors and hormones linked to an increased risk of cancer.”

The investigators evaluated plasma growth factors and hormones in 21 sedentary people (mean age, 53.0 ± 11 years) who had been eating a low-protein, low-calorie diet for 4.4 ± 2.8 years; 21 endurance runners matched by body mass index (BMI); and 21 age- and sex-matched sedentary people eating Western diets.

Compared with the Western-diet group, the low-protein, low-calorie diet group and the runner group had lower BMIs (26.5 ± 2.7, 21.3 ± 3.1, and 21.6 ± 1.6 kg/m², respectively; P < .005). The low-protein, low-calorie diet group and the runner group also had lower plasma concentrations of insulin, free sex hormones, leptin, and C-reactive protein, and had higher sex hormone–binding globulin (SHBG) than did the Western-diet group (all P < .05).

The low-protein, low-calorie diet group had the lowest level of plasma insulin-like growth factor I (IGF-I; 139 ± 37 ng/mL) and concentration ratio of IGF-I to IGF binding (0.033 ± 0.01), compared with 177 ± 37 ng/mL and 0.044 ± 0.01, respectively, in the runner group, and 201 ± 42 ng/mL and 0.046 ± 0.01, respectively, in the Western-diet group (P < .005).

Study limitations include cross-sectional design, inability to determine true causal relations or to evaluate the prevalence of cancer, and small sample size. The authors also note that a low-protein diet can have detrimental effects on bone mass and strength in elderly people with already low serum IGF-I concentrations.

“Exercise training, decreased adiposity, and long-term consumption of a low-protein, low-calorie diet are associated with low plasma growth factors and hormones that are linked to an increased risk of cancer,” the authors write. “Low protein intake may have additional protective effects because it is associated with a decrease in circulating IGF-I independent of body fat mass.”

Clinical Nutrition Research, the General Clinical Research Center, and the Diabetes Research and Training Center supported this study. The authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2006;84:1456-1462.

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:

• Describe the effects of a low-protein, low-calorie diet and high physical-activity level on markers of cancer risk.
• Describe the protective effect of a low-protein, low-calorie diet on markers of cancer risk.

Clinical Context

According to the authors of the current study, a high-protein, high-calorie diet with little physical activity and high adiposity contribute to cancer risk. Possible mechanisms for this include the increase in circulating concentrations of growth factors, anabolic hormones, and inflammatory cytokines, and a decrease in circulating concentrations of SHBG. The effects of long-term lifestyle modifications on factors linked to increased cancer risk have not been sufficiently investigated. These factors include IGF-I, insulin, free sex hormones, and C-reactive protein.

This cross-sectional comparison study examines serum markers of cancer risk in 3 groups of middle-aged men and women: sedentary people eating a low-protein, low-calorie diet; physically active people eating a typical Western diet; and sedentary people eating a typical Western diet.

Study Highlights

• 3 groups of adult subjects were identified and recruited.
• The low-protein, low-calorie sedentary (less than 1 hour of endurance physical activity weekly) group (n = 21), recruited through the St. Louis Vegetarian Society and an online raw-food magazine, had been consuming a raw-plant diet for at least 2 years.
• The high physical-activity group (n = 21), recruited from a running club, participated in high endurance running for at least 48 miles weekly for an average of 21 years and consumed a typical Western diet.
• Healthy nonobese sedentary control subjects (n = 21), recruited through an advertisement, had a BMI of less than 30 kg/m², and consumed a typical Western diet.
• None of the subjects had a chronic illness, and their weight had been stable for at least 6 months.
• Each subject underwent complete medical evaluation with blood tests and urinanalysis.
• Subjects recorded 7-day food diaries, which were analyzed by the Nutrition Data System.
• For the blood tests, subjects fasted overnight and then had total body-fat mass and lean body mass measured with dual energy X-ray absorptiometry.
• Plasma testosterone, estradiol, SHBG, IGF-I, IGF binding protein 3 (IGFBP-3), dehydroepiandrosterone sulphate (DHEAS), insulin, C-peptide, leptin, and C-reactive protein levels were determined.
• Daily energy intake was significantly lower in the low-protein, low-calorie group than in the runner and control groups.
• The runner and control groups ate typical Western diets, including foods from both plants and animals, with no differences in trans fatty acid or total dietary fiber intake.
• BMI, percentage of body fat, trunk weight, and truncal fat were significantly lower in the low-protein, low-calorie and runner groups than in the control group.
• Both IGF-I and IGFI:IGFBP-3 were significantly lower in the low-protein, low-calorie group than in the runner group, but were similar in the runner and control groups.
• The association remained even after controlling for BMI and body-fat mass, suggesting that the protective effect is related to dietary factors.
• Fasting plasma insulin and C-peptide concentrations were lower in the low-protein, low-calorie and runner groups than in the control group.
• SHBG concentrations were much higher in the low-protein, low-calorie and runner groups than in the control group.
• SHBG concentrations were inversely correlated with plasma C-peptide and plasma IGF-I concentrations.

Pearls for Practice

• A low-protein, low-calorie diet and endurance physical activity are associated with a decrease in plasma factors associated with some types of cancer.
• The protective effect of a low-protein, low-calorie diet is independent of body-fat mass and is likely mediated by dietary factors.