Role of Decreased Food Intake with or Without Increased Physical Activity

There are also four underfeeding studies that have examined changes in TEE with negative energy balance achieved by a reduction in energy intake. As shown in Table 5-31, the reduction in energy intake in these studies ranged from 758 to 1,620 kcal/d and was associated with a reduction in TEE that averaged 36 percent of the reduction in energy intake. It should be noted that there was a period of 3 to 52 weeks of underfeeding between the measurements of TEE made during weight maintenance and negative energy balance. Thus, some of the reduction in TEE was due to reduced energy requirements associated with reduced body weight.

2,200"

2 3

2,000"

Energy Expendi (kcal/day)

1,800 -1,600 -1,400 -

en c

1,200 -

OC

1,000 -

800

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Overfeeding Underfeeding

2,000 1,800 1,6001,400 1,2001,000' 800

FIGURE 5-9 Relationship between changes in fat-free mass and resting energy expenditure during overfeeding and underfeeding. Reprinted, with permission, from Saltzman and Roberts (1995). Copyright 1995 by International Life Sciences Institute.

FIGURE 5-9 Relationship between changes in fat-free mass and resting energy expenditure during overfeeding and underfeeding. Reprinted, with permission, from Saltzman and Roberts (1995). Copyright 1995 by International Life Sciences Institute.

In multiple regression analyses using the DLW data of the studies in Table 5-31, weight, age, and gender significantly predicted TEE, and the b-coefficient for the weight term was 16.6 kcal/d. This implies that for weight-stable individuals, differences in body weight of 1 kg are associated with differences in TEE of 16.6 kcal/d. By correcting the changes in TEE that can be attributed to the decrease in body size in the four underfeeding studies described in Table 5-31, 8.4 percent of the reduction in TEE was unaccounted for by weight loss and appears therefore to be associated with a state of negative energy balance. This could be due to a reduction in energy expenditure per kg body weight or to a decrease in physical activity.

These values can be used to estimate the anticipated reduction in metabolizable energy intake necessary to achieve a given level of weight loss, if weight loss is achieved solely by a reduction in energy intake and there is no change in energy expenditure for physical activity. For example, a weight loss of 1 to 2 lb/wk (65 to 130 g/d) is equivalent to a body energy loss of 468 to 936 kcal/d, because the energy content of weight loss averages 7.2 kcal/g (i.e., 75 percent fat containing 9.25 kcal/g and 25 percent FFM containing 1 kcal/g) (Saltzman and Roberts, 1995). Taking into account the decrease in TEE due to weight loss (16.6 kcal/kg) and due to negative energy balance (8.4 percent of initial TEE), the total expected reduction in TEE after 10 weeks of dieting is predicted to be 376 to

ENERGY 215

TABLE 5-31 Changes (A) in Total Energy Expenditure (TEE) During Underfeeding Studies"

ATEE ABEÄ AEIC Reference (kcal/d) (kcal/d) (kcal/d) ATEE/AEI Coor ATEE/ AEId

TABLE 5-31 Changes (A) in Total Energy Expenditure (TEE) During Underfeeding Studies"

ATEE ABEÄ AEIC Reference (kcal/d) (kcal/d) (kcal/d) ATEE/AEI Coor ATEE/ AEId

Heyman et al., 1992

-297

-461

-758

0.392

0.076

Kempen et al., 1995

-359

-765

-1,124

0.319

0.087

Racette et al., 1995

-349

-695

-1,044

0.334

0.079

van Gemert et al.,

-645

-975

-1,620

0.398

Means 0.361 0.084

2000

Means 0.361 0.084

a Where all values are in kcal/d, A describes changes in value between weight maintenance and underfeeding. b BE = body energy.

c EI = energy intake (calculated as ABE + ATEE).

d CorrATEE is change in total energy expenditure after subtracting the estimated change in TEE due to weight loss in the underfeeding period prior to measurement of TEE. This value indicates the change in TEE is due to negative energy balance rather than weight loss. It was estimated as weight loss prior to the underfeeding TEE x 16.6, where 16.6 is the weight coefficient in the relationship, TEE = constant + weight + age + gender in the doubly labeled water data from these studies.

542 kcal/d for an individual with an initial weight maintenance TEE of 2,500 kcal/d. Therefore, to maintain a rate of weight loss of 1 to 2 lb/wk, the reduction in energy intake would need to be 844 (468 + 376) to 1,478 kcal/d (936 + 542) after 10 weeks of weight loss.

This calculation serves both to emphasize the importance of exercise in helping prevent reduced TEE during weight loss, and to illustrate the relatively high level of reduction in energy intake needed when weight loss is to be achieved by dieting alone. It should be noted that the above calculations were based on TEE data derived from studies in adults in which reduction in energy intake was in the range of 758 to 1,620 kcal/d. The impact on energy expenditure of weight loss regimens involving lesser or greater reductions in energy intake need to be assessed before rates of weight reduction can be more precisely predicted. However, it must be appreciated that reduction in resting rates of energy expenditure per kilogram of body weight have a small impact on the prediction of energy deficits imposed by food restriction, and the greatest cause of deviation from projected rates of weight loss lies in the degree of compliance. The coefficient of 16.6 kcal/kg of weight loss calculated from the data in Table 5-31 could be utilized to anticipate the reduction in energy intake required for maintaining lower body weights. Further studies in this area are needed.

216 DIETARY REFERENCE INTAKES

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