High protein intake increases daily fat oxidation; effect of protein intake and physical activity on the 24 h pattern and rate of macronutrient utilization. Forslund, Anders H., Antoine E. El-Khoury, Roger M. Olsson, Anders M. Sj[diaeresis]odin, Leif Hambraeus, Vernon R. Young. aDepartment of Medical Sciences, Nutrition, Uppsala University, Uppsala, Sweden, bLaboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, MA, USA
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APStracts 6:0023E, 1999.
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Effects of moderate physical activity (90 min at 45-50% of VO2max 2 times daily) and _high_ (2.5 g protein _ kg-1 _ [delta]-1, n=6) or _normal_ protein intake (1.0 g protein_ kg-1 _ [delta]-1, n=8) on the pattern and rate of 24h macronutrient utilization in healthy adult men were compared after a diet-exercise-adjustment period of 6 days. Energy turnover (ET) was determined by indirect and direct (suit)calorimetry and "protein oxidation" by a 24h continuous iv infusion of [1-13C]leucine. Subjects were in slight positive energy balance during both studies. Protein contributed to a higher (22 vs10%) and carbohydrate (CHO) a lower (33 vs 58%) proportion of total 24h ET on the high vs normal protein intake. The highest contribution of fat to ET was seen postexercise during fasting (73% and 61% of ET, for high and normal respectively). With the _high_ protein diet the subjects were in a positive protein (p<0.001), and CHO balance (p<0.05) and a negative fat balance (p<0.05). The increased energy turnover post-exercise was not explained by increased rates of urea production and/or protein synthesis
Summary:
The aim of this study was to evaluate the effect of a high-protein intake compared with a “normal”-protein intake on energy substrate utilization (burning protein, fat or carbohydrate for energy). Fourteen men were placed on a standardized diet and exercise regimen for six days. Then, six of the men were placed in a “high-protein" group, lowering carbohydrate content from 58% to 33% (consuming 2.5 grams of protein per kilogram bodyweight) while eight were placed in a “normal-protein” group (consuming 1 gram of protein per kilogram of bodyweight). All subjects exercised for 90 minutes each day on a stationary bicycle. On days when their blood was tested, subjects engaged in two 90-minute bike workouts. When comparing diets, the high-protein, lower-carbohydrate group used more protein for energy during exercise. However, there was no effect on total 24-hour protein utilization. Subjects on the high-protein diet used more fat for energy during exercise as well as during recovery and at rest, compared with the “normal”-protein group. In addition to burning fat for energy, subjects on the high-protein lower- carbohydrate diet were also in positive nitrogen balance, which prevents the body from breaking down body tissue, such as muscle.
Commentary:
The findings of this study can be applied to the Atkins Principle of Good Health. Consuming a diet higher in protein and lower in carbohydrate while exercising 90 minutes per day, subjects were able to stay in positive nitrogen balance. These subjects also used more fat for energy during exercise, during recovery and at rest than the “normal”-protein group.
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