Is it Time to Revise Atwater Energy Values of Some Foods?

Transcription

1 Is it Time to Revise Atwater Energy Values of Some Foods? Edward Farnworth, PhD; Private Consultant, Ottawa, Canada Karen Lapsley, DSc; Almond Board of California, Modesto 1

2 Overview - Atwater Energy Values of Foods Dr. W.O. Atwater determined energy values for many foods over 100 years ago. He based these calculations on a small number of human subjects BUT applied to food groups (grains, legumes, fruits ) NOT individual foods. Atwater values are used world-wide and considered in most cases still to be good enough. Consumers refer to the calorie content of foods rather than the energy value of foods. Many human nutrition / metabolism textbooks do not refer to Atwater values or how they are derived. Atwater values are not covered in most nutrition / dietetics course in any depth. Does not keep up with changes and variety in the food supply. 2

3 Food Energy Available to the Body Metabolizable Energy Gross Energy Intake (GEI) Digestible Energy Fecal Energy Metabolizable Energy Urinary Energy ME = GEI - GEfeces - GEurine National Academy Press,

4 Assumptions Made When Calculating the Atwater Energy Value of a Food Protein, lipid, & carbohydrate composition of the food are known BUT: carbohydrate calculated by difference or a variety of analytical methods the digestibility of the food was determined precisely BUT: often no data available for individual foods only fecal & urinary energy need to be accounted for BUT: specific heat of eating may need to be accounted for 4

5 Is there enough new data to support the revision of energy values for almonds and other plant foods? Since Atwater s time there have been criticisms and scientific advances (e.g. standard vs modified values) better understanding of digestion, absorption, metabolism improved knowledge on the effect of food structure on digestibility (e.g. almonds vs pistachios) improved clinical trial designs advanced compositional analyses, especially for carbohydrates (fiber) In some foods, the fiber content is significant. This may have an impact on the Atwater energy value. 5

6 Composition of select nuts, legumes, seeds, g/100g USDA SR25 (2012) Water Protein Dietary fiber Sugars + Starch Total lipid (fat) Almonds Pistachios Walnuts Chickpeas* Lentils* <1 Soybeans* Sesame <1 50 Sunflower Pumpkin * cooked 6

7 It may be necessary to re-evaluate the Atwater energy values for some foods 7

8 For example: Is the energy value for almonds correct? The tabulated Atwater energy value for almonds is 6.1 kcal/g Results from recent clinical trials (diets including almonds) indicate inconsistencies when expected (calculated) energy intakes are compared with measured body weight gains and energy intakes The cell structure of almonds differs from other tree nuts Studies show that mastication affects nutrient availability, especially lipid availability in almonds 8

9 Macronutrient absorption from almonds: the measured energy value of almonds Location: USDA, Beltsville Human Nutrition Research Center Objective: To empirically determine the metabolizable energy value of almonds To determine the effect of consuming almonds on macronutrient digestibility Hypothesis: USDA, Beltsville Human Nutrition Research Center The metabolizable energy value of almonds will be lower than predicted from their chemical composition because of reduced fat digestibility JA Novotny, SK Gebauer, and DJ Baer. Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets. Am. J Clin Nutr August; 96(2):

10 Study design Study Design Randomized, crossover, controlled-feeding, weightmaintenance study in healthy adults (n = 18) Three 18-day diet periods, each separated by a 7-day compliance break Diet Period 1 Break Diet Period 2 Break Diet Period 3 Adaptation + Collection Adaptation + Collection Adaptation + Collection 9 days 9 days 7 days 9 days 9 days 7 days 9 days 9 days Collection phase: all fecal and urine samples collected 3 different doses of dry roasted almonds 0 g/d (control) 1.5 oz/d (42 g/d) 3.0 oz/d (84 g/d) Partial replication of treatment (to estimate subject x diet interaction) 10

11 Controlled-feeding study Participants were required to consume all foods provided during diet periods Not permitted to consume any outside foods Breakfast and dinner consumed at the Beltsville Human Nutrition Research Center, Mon-Fri Lunch and weekend meals were packed for offsite consumption 11

12 Study Conclusions Fat digestibility of the total diet: Decreased by 5% (1.5 oz/d) and nearly 10% (3.0 oz/d) Energy digestibility of the total diet: Decreased by ~3% (1.5 oz/d) and 5% (3.0 oz/d) The energy value for almonds calculated from the digestibility data was not dose dependent Measured energy density of almonds was determined to be 4.6 kcal/g vs. 6.1 kcal/g as predicted by Atwater factors 20% fewer calories in a 1 oz svg of almonds than listed on the nutrition label with new method for calculating calories 12

13 Energy (kcal/1 oz svg) Measured Energy Value of Almonds 180 P < kcal kcal/g 4.6 kcal/g 80 0 Predicted Measured 13

14 Other foods that may have Atwater energy values that should be re-evaluated Oats Other nuts Legumes Pulses Foods high in fiber 14

15 Thank-you for your attention Acknowledgements : D. Baer, J. Novotny, S. Yada 15