LE Kelemen, LH Kushi, DR Jacobs Jr., JR Cerhan Mayo Clinic College of Medicine, Rochester, MN

1. Substitution of Dietary Protein for Carbohydrate: Associations of Disease and Mortality in a Prospective Study of Postmenopausal Women LE Kelemen, LH Kushi, DR Jacobs Jr., JR Cerhan Mayo Clinic College of Medicine, Rochester, MN University of Minnesota, Minneapolis, MN Kaiser Permanente, Oakland, CA

2. Background • Popular high protein (HP) diets extol benefits for weight loss • Often do not discriminate among protein types • Effect of protein & protein type on long term health outcomes not widely studied

3. Objectives Using multivariable nutrient density models: • To estimate the effect of an isoenergetic substitution of total protein for total carbohydrate with cancer incidence and mortality from cancer, CHD and all causes in the IWHS • To estimate the effect of an isoenergetic substitution of one type of protein for another type of protein with these outcomes

4. Study Population • In 1986: 99,826 Iowa women aged 55-69 yrs (now 71-86) • Identified from randomly selected driver’s licenses • Mailed questionnaire • diet (FFQ) • self-reported lifestyle, medical & reproductive history • 41,836 (41.9%) enrolled

5. Dietary Assessment • Semi-quantitative Harvard FFQ • Validation study, 1988, 44 Iowa women • average of five 24-hour recalls over 2 months: • r = 0.16 ( protein) • r = 0.45 (carbohydrate) • r = 0.43-0.62 (fats) • Reproducibility (2.5 yrs) • r = 0.59 (protein) • r = 0.53 (carbohydrate) • r = 0.47-0.57 (fats)

6. Follow-Up • Questionnaires mailed in 1987, 1989, 1992 and 1997 • Incident cancers identified by linkage to Iowa SEER cancer registry • Deceased non-respondents & cause of death identified by linkage to National Death Index • 15 years follow-up

7. Eligibility Criteria Excluded • Premenopausal women (n=569) • Prior history of cancer (n=3,881) • Known heart disease (n=5,116) • Known diabetes (n=2,675) • Diet •  30 blanks on FFQ • total energy (kcal/d)  600 or  5,000 (n=3,096) • 29, 017 eligible women

8. Data Analysis • Dietary exposures • Macronutrients expressed as nutrient densities (i.e. % of energy from protein, carbohydrate and fats) • Micronutrient covariates were energy-adjusted (Willett & Stampfer 1986) • Categorized into quintiles • RR (95% CI) estimated using Cox proportional hazards with lowest intake category as referent; age as time metric

9. Data Analysis • Multivariable-adjusted nutrient density models (Willett 2nd ed 1998 p 295; Hu AJE 1999; Willett AJCN 1997) • Estimate associations from an increase in the % energy from protein intake • By forcing total energy and other intake (i.e., dietary fats) to be constant, and by excluding carbohydrate from the model, modeling the effects of an increase in protein intake, by definition, statistically results in a decrease in carbohydrate intake • Thus, the effect estimates of protein assume a substitution interpretation • The % of energy from protein that is “substituted” for carbohydrate is the difference between the median intake in the highest and lowest quintiles • Models also adjusted for other risk factors

10. Covariates • Known/suspected confounders & risk factors: • Total energy • Fats (saturated, poly-, mono- & trans) (all quintiles & expressed as % of energy) • Total fiber, dietary cholesterol, dietary methionine (all quintiles & energy-adjusted) • Alcohol (≤14 vs > 14 g/d) • Smoking (never, former, current) • Activity level (active vs not active) • BMI (5 levels) • History of HTN • PM hormone use • Education (≤ high school vs > high school) • Family history of cancer • Multivitamin use • Vitamin E supplement use

11. Results • 475,755 person-years • Outcomes: • 4,843 incident cancers • 739 CHD deaths • 1,676 cancer deaths • 3,978 deaths from all causes

12. Table 1 Distribution of baseline characteristics by quintiles of total protein among 29,017 Iowa women, 1986

13. Table 1 cont.

14. Table 1 cont. A composite of beef, pork, processed meat B composite of milk, cream, ice-cream, yogurt, cheese C composite of dark bread, brown rice, oatmeal, whole grain cereal, bran, wheat germ & other grains (bulgar, kasha, couscous) D composite of rice, pasta, potatoes, refined cold breakfast cereal, muffins, snack foods, sweetened sodas, pizza, chocolate, cakes, cookies

15. Table 2 RR (95% CI) for CHD mortality by quintiles of total protein intake (% energy) substituted for isoenergetic amount of carbohydrate, IWHS 1986 to 2001 *adjusted for dietary fats, total energy plus other covariates

16. Table 3 RR (95% CI) for cancer incidence by quintiles of total protein intake (% energy) substituted for isoenergetic amount of carbohydrate, IWHS *adjusted for dietary fats, total energy plus other covariates

17. Table 4 RR (95% CI) for cancer mortality by quintiles of total protein intake (% energy) substituted for isoenergetic amount of carbohydrate, IWHS *adjusted for dietary fats, total energy plus other covariates

18. Table 5 RR (95% CI) for all cause mortality by quintiles of total protein intake (% energy) substituted for isoenergetic amount of carbohydrate, IWHS *adjusted for dietary fats, total energy plus other covariates

19. Table 6 RR (95% CI) of vegetable protein intake (% of energy) substituted for isoenergetic amount of animal protein for different outcomes *adjusted for carbohydrate, dietary fats, total energy, plus other covariates

20. Table 7 Multivariable RR* for protein foods substituted for an isoenergetic amount of carbohydrate foods (svgs/1000 kcals) for different outcomes *adjusted for dietary fats, total energy, other covariates & quintiles of svgs/1000kcals: fruits & veg, eggs, poultry, fish, legumes, dairy, red meats

21. Summary • Similar ↓ in risk of CHD mortality when vegetable protein substituted for carbohydrate or animal protein • suggests animal protein & carbohydrate may have similar potentially adverse effects on CHD mortality • Animal protein not associated with any outcome • ↑ risk ofCHD mortality for red/processed meat servings (RR=1.44) and dairy servings (RR=1.41) when substituted for carbohydrate foods • Modest risk of red/processed meat servings with all cause mortality (RR=1.16) • Modest risk of legume servings with cancer mortality (RR=1.23) but not with cancer incidence • No associations with cancer incidence

22. Strengths & Limitations • Strengths • Prospective • Large # of events • Adjust for large # of covariates • Limitations • Baseline diet only • No blood samples • Food substitution analyses: measuring non-protein components? • Red meat & CHD – consistent with others’ findings (Snowdon 1984, Hu 1999, Liu 2004)

23. Conclusions • Dietary protein from animal and vegetable sources appear to be differentially associated with mortality from CHD & all causes when substituted in the diet • Long-term adherence to popular HP diets, without discrimination toward protein source, may have potentially adverse health consequences

24. Appendix - Protein Food Groupings • Legumes/nuts/tofu • composite of tofu, dried beans, nuts and peanut butter • Dairy • composite of milk, cream, ice-cream, yogurt and cheese • Eggs • Red meats • composite of beef, pork and processed meat • Poultry • composite of chicken and turkey • Fish • composite of fresh fish, canned fish and seafood • Fruits & Vegetables • Including juices, excluding potatoes • Carbohydrate foods = referent • composite of refined carbohydrates (rice, pasta, potatoes, refined cold breakfast cereal, muffins, snack foods, sweetened sodas, pizza, chocolate, cakes, cookies), and • whole grain carbohydrates (dark bread, brown rice, oatmeal, whole grain breakfast cereal, bran, wheat germ and other grains such as bulgar, kasha and couscous)