FITNESS AND THE EFFECT OF EXERCISE TRAINING ON THE DIETARY-INTAKE OF HEALTHY ADOLESCENTS

OBJECTIVE: In healthy, nonobese, adolescent males and females to: (1) Determine the relationship between fitness and energy intake; (2) asse ss the effect of five-weeks endurance training on energy intake and fo od choice and (3) compare food record assessments of energy intake wit h doubly-labeled water (DLW) measurement of total energy expenditure ( TEE). DESIGN: (1) Cross sectional analysis of fitness and food intake and (2) Prospective, randomized, controlled interventional study of en durance-type exercise training in 44 females and 44 males (age range, 15-17 y). MEASUREMENTS: Pre and end interventional three day food reco rds were successfully collected from 32 females (15 controls, 17 train ed) and 39 males (19 controls, 20 trained). Fitness was assessed from cycle ergometry as peak oxygen uptake normalized both to thigh muscle mass and body weight. Thigh muscle mass was measured by magnetic reson ance imaging. TEE using the DLW technique was measured in 12 females ( 6 controls, 6 trained) and 20 males (10 controls, 10 trained) during w eeks 4-5 of the exercise training program (simultaneously with the sec ond assessment of food records). Food record data were analyzed using the Minnesota Nutrition Data System. RESULTS: Fitness was correlated w ith self reported total caloric intake in males but not females. In fe males, there was a significant increase in fat intake (19.8 +/- 9%, P < 0.05) and a significant decrease in carbohydrate intake (-9.8 +/- 4% ) in the trained subjects. No changes were observed in the control sub jects. Energy expenditure (2072 +/- 52 kcal/d) was significantly great er than the estimated energy intake (1520 +/- 112 kcal/d, P < 0.007) d uring the intervention in the trained, but not control, subjects. Howe ver, there was no weight change in either control or trained subjects. In males, no changes were observed in food choice in either control o r trained subjects. Similar to the females, energy expenditure (2425 /- 22 kcal/d) was significantly greater than the estimated energy inta ke (2168 +/- 117 kcal/d, P < 0.05) during the intervention in the trai ned, but not control, subjects. No weight changes were observed in eit her group. CONCLUSIONS: Fitness is associated with increased self-repo rted energy intake in males but not females, while exercise training l ed to alterations in food selection (greater fat and reduced carbohydr ate) only in females. These observations could reflect specific gender differences, or, alternatively, the generally lower levels of fitness in the females. The apparent negative energy balance without evidence for weight loss in both the trained males and females suggests a syst ematic under reporting of food intake during exercise programs in adol escents, and indicates the possibility that errors in self reported fo od intake might be greater during transitions from one level of energy expenditure to another.