Contents lists available at ScienceDirect Journal of Thermal Biology journal homepage: www.elsevier.com/locate/jtherbio Postprandial energy expenditure of protein is affected by its phosphorus content Lina Abdouni, Ammar Olabi, Omar Obeid ⁎ Department of Nutrition and Food Sciences, American University of Beirut, Beirut, Lebanon ARTICLE INFO Keywords: Phosphorus Postprandial energy expenditure Normal protein High protein ABSTRACT Postprandial energy expenditure (PEE) is largely dependent on ATP production, which is may be affected by phosphorus (P) availability. Proteins are known to have high levels of P and induce high levels of PEE. This study aimed at assessing the effect of P in PEE of normal and high protein meals. A single-blind randomized crossover study was conducted with two groups of 12 healthy lean male subjects who received iso-caloric (554 Kcal) meals. Group1: normal protein (NPr) meal with or without P (500 mg) and group 2: high protein (HPr) meal with or without P (500 mg), on two visits separated by a minimum of 1-week washout period. Energy expenditure and substrate oxidation were measured at baseline and every 30 min for 4 h after meal ingestion using a ventilated hood for indirect calorimetry. NPr and HPr meals had similar postprandial energy expenditure and this was significantly increased (P = 0.005) by P ingestion. Our work shows that PEE of protein meal is highly affected by P content of the meal. 1. Introduction Postprandial energy expenditure (PEE) covers the cost of digestion, absorption, transport, and storage of the ingested food and is related to ATP production (Scott and Devore, 2005). PEE is the least reproducible component of total daily energy expenditure because it is affected by many external (e.g. food composition, etc.) and internal (e.g. hormonal status, etc.) factors (Acheson et al., 2011; Scott and Devore, 2005; Tentolouris et al., 2008). Among macronutrients, PEE of proteins is known to be the highest (Acheson et al., 2011; Karst et al., 1984; Scott and Devore, 2005; Smeets et al., 2008) and this is paralleled by the fact that the body has no storage capacity of excess protein and thus, free amino acids are either assimilated into protein or oxidized. Accord- ingly, protein turnover was suggested to account for most (~68%) of the thermogenic effect of proteins (Paddon-Jones et al., 2008) as the energy costs of protein synthesis and protein breakdown are estimated to be 3.6 and 0.7 KJ/g, respectively (Veldhorst et al., 2009). However, the wide variations in PEE between proteins even for those of high biological values (Acheson et al., 2011; Karst et al., 1984) raise a question on whether other factors are involved in PEE of proteins. This encouraged us to assume a role for P, since most proteins contain high levels of bioavailable P. ATP production is affected by the availability of P (Morris et al., 1978) and is important for several processes that are known to influ- ence eating behavior and energy expenditure (Obeid et al., 2010). In- gestion of low P containing carbohydrates, e.g. refined cereals, caloric sweeteners, potatoes etc., is accompanied by a stimulation in insulin release which is known to increase the peripheral P uptake and the phosphorylation of many compounds. This is believed to compromise the availability of P to fulfill the requirements of all processes, including ATP production which can act as a phosphate donor (Karczmar et al., 1989). Data on the impact of P ingestion on the postprandial energy metabolism of protein manipulated meals are limited. The aim, there- fore, of the present study was to investigate the effect of P ingestion on PEE and substrate oxidation in healthy lean male subjects. This entailed consuming two iso-caloric meals, a normal protein (NPr) and a high protein (HPr) meal, using egg white protein that has high biological value and is almost devoid of P (Kalantar-Zadeh et al., 2010), as the main source of protein. 2. Methods 2.1. Study design and participants The study was a single-blind, randomized, and placebo-controlled crossover clinical trial conducted between September 2015 and June https://doi.org/10.1016/j.jtherbio.2018.10.013 Received 19 April 2018; Received in revised form 9 October 2018; Accepted 13 October 2018 Abbreviations: PEE, postprandial energy expenditure; %CO, percentage of carbohydrate oxidation; %FO, percentage of fat oxidation ⁎ Correspondence to: Department of Nutrition and Food Sciences, Faculty of Agricultural and Food Sciences, American University of Beirut, P.O. Box 11-0236, Beirut, Lebanon. E-mail address: omar.obeid@aub.edu.lb (O. Obeid). Journal of Thermal Biology 78 (2018) 214–218 Available online 19 October 2018 0306-4565/ © 2018 Elsevier Ltd. All rights reserved. T