Dietary protein and urinary nitrogen in relation to 6-year changes in fat mass and fat-free mass.
BACKGROUND
In contrast to the physiological expectation, observational studies show that greater protein intake is associated with subsequent body weight (BW) gain. An increase in fat-free mass (FFM) due to the anabolic effects of protein could explain this.


OBJECTIVE
To examine associations between protein intake and subsequent changes in fat mass (FM) and FFM in longitudinal, observational data.


METHODS
A health examination, including measures of FM and FFM by bioelectrical impedance at baseline and follow-up 6 years later, was conducted. Diet history interviews (DHI) were performed, and 24-h urinary nitrogen collection at baseline was done. In total, 330 participants with DHI, of whom 227 had validated and complete 24-h urine collection data, were analyzed. Macronutrient energy substitution models were used.


RESULTS
Mean estimated protein intake was 14.6 E% from DHI and 11.3 E% from urinary nitrogen. Estimated from DHI, FM increased 46 g per year, with every 1 E% protein substituted for fat (95% confidence interval (CI) = 13, 79; P = 0.006), and FFM increased 15 g per year (1, 30; P = 0.046). Results were similar in other substitution models. Estimated from urinary nitrogen, FM increased 53 g per year, with 1 E% protein substituted for other macronutrients (24, 81; P < 0.0005), and FFM increased 18 g per year (6, 31; P = 0.004).


CONCLUSIONS
Within a habitual range, a greater protein intake was associated with BW gain, mostly in FM. This is in contrast to the expectations based on physiological and clinical trials, and calls for a better understanding of how habitual dietary protein influences long-term energy balance, versus how greater changes in dietary proteins may influence short-term energy balance.
1] Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark [2] Faculty of Medical and Health Sciences, University of Copenhagen, Copenhagen, Denmark.
M Z
MZ
Ankarfeldt
Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark.
K
K
Gottliebsen
Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark.
L
L
Ängquist
Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
A
A
Astrup
1] Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark [2] The Boden Institute of Obesity, Nutrition, Exercise & Eating Disorders, University of Sydney, Sydney, Australia [3] National Institute of Public Health, University of Southern Denmark, Odense, Denmark.
B L
BL
Heitmann
1] Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark [2] The Novo Nordisk Foundation Centre for Basic Metabolic Research, Faculty of Medical and Health Sciences, University of Copenhagen, Copenhagen, Denmark.
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TI
Sørensen
D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D001823:Body Composition; D015992:Body Mass Index; D004044:Dietary Proteins / Q000378:metabolism*; D017097:Electric Impedance; D002149:Energy Intake; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine*; D009749:Nutrition Surveys; D009747:Nutritional Physiological Phenomena; D009765:Obesity / Q000209:etiology / Q000378:metabolism* / Q000517:prevention & control; D012307:Risk Factors; D015430:Weight Gain
D004044:Dietary Proteins; D009584:Nitrogen