Extra Energy Costs

The cost of growth amounts to 10-25 kJ/g of new tissue deposited; the value is higher if fat with little lean tissue is laid down. A newborn has a high energy requirement of approximately 460 kJ/kg, with a cost of weight gain amounting to 26kJ/g; however, by 1 year of age the total daily requirement decreases to approximately 335 kJ/kg as growth slows, with growth now costing 10kJ/g. Breast-fed infants have an energy requirement approximately 10% lower than that of bottle-fed infants (Table 4).

Table 4

Average energy requirements of infants (breast and bottle fed) and of children up to age 18years

Infants

Energy requirement

Children

Weight

PAL

Energy

Weight

PAL

Energy

(months)

(kJ/kg/day)

(years)

(kg)

requirement

(kg)

requirement

(kJ/kg/day)

(kJ/kg/day)

Boys

Girls

Mean

Boys

Girls

1

475

445

460

1.1-2

11.5

1.43

345

10.8

1.42

335

2

435

420

430

2.1-3

13.5

1.45

350

13.0

1.42

337

3

395

395

395

3.1-4

15.7

1.44

334

15.1

1.44

320

4

345

350

345

4.1-5

17.7

1.49

322

16.8

1.49

309

5

340

345

345

5.1-6

19.7

1.53

312

18.6

1.53

299

6

335

340

340

6.1-7

21.7

1.57

303

20.6

1.56

290

7

330

330

330

7.1-8

24.0

1.60

295

23.3

1.60

279

8

330

330

330

8.1-9

26.7

1.63

287

26.6

1.63

267

9

330

330

330

9.1-10

29.7

1.66

279

30.5

1.66

254

10

335

330

335

10.1-11

33.3

1.71

270

34.7

1.71

242

11

335

330

335

11.1-12

37.5

1.75

261

39.2

1.74

229

12

335

330

335

12.1-13

42.3

1.79

252

43.8

1.76

217

13.1-14

47.8

1.82

242

48.3

1.76

206

14.1-15

53.8

1.84

233

52.1

1.75

197

15.1-16

59.5

1.84

224

55.0

1.73

189

16.1-17

64.4

1.84

216

56.4

1.73

186

17.1-18

67.8

1.83

210

56.7

1.72

185

The energy requirements of infants were derived from double-labeled water measurements of total energy expenditure to which was added the age-specific energy deposited during growth, taking into account the different proportions of lean and fat tissue laid down during infancy. The children's requirements were estimated from quadratic equations relating body weight to total energy expenditure of girls and boys measured separately or from estimates of total energy expenditure based on calibrated heart rate recordings. Again, the energy deposited as growth was added to give a requirement expressed on a weight basis to allow adjustments for children of different weights at each age.PAL, physical activity level.

The energy requirements of infants were derived from double-labeled water measurements of total energy expenditure to which was added the age-specific energy deposited during growth, taking into account the different proportions of lean and fat tissue laid down during infancy. The children's requirements were estimated from quadratic equations relating body weight to total energy expenditure of girls and boys measured separately or from estimates of total energy expenditure based on calibrated heart rate recordings. Again, the energy deposited as growth was added to give a requirement expressed on a weight basis to allow adjustments for children of different weights at each age.PAL, physical activity level.

Without sufficient energy, a child will fail to grow, but the causes of growth failure usually relate to a deficiency of other nutrients or to infection rather than to a lack of dietary energy. Adolescents, particularly boys, who are physically very active may have a high demand for energy. However, the actual cost of even rapid growth rates at this age is modest.

Traditionally, pregnancy is considered, incorrectly, a time of great demand for food. Good nutrition is extremely important, and a weight gain in pregnancy of approximately 12 kg is desirable for reducing the risk of maternal and fetal complications and preterm and low-birth-weight infants and increasing the probability of delivering a 3.3-kg infant. With a weight gain of 12 kg, increases in maternal BMR are 5, 10, and 25% in the first, second, and third trimester of pregnancy, respectively. In practice, the intensity of physical activity often declines, particularly in late pregnancy, and some enhanced metabolic efficiency seems to occur. Thus, the increase in total energy expenditure amounts to only 1, 6, and 17% in the three trimesters, respectively. Therefore, the need for additional energy is small, amounting to 85, 350, and 1300 kJ/ day (20, 85, and 310kcal/day) for sequential trimesters, and in practice this means that a pregnant women needs to increase her food intake by 1.5MJ/day (360kcal/day) in the second trimester and 2.0MJ/day (475 kcal/day) in the third trimester.

Lactation imposes a greater demand on mothers since their milk contains 1.9MJ/day after birth, increasing to approximately 2.3 MJ/day on exclusive breast-feeding at 3 months. Extra energy is involved in making this milk, and the total extra energy demand is 2.6MJ/day. Part of this additional energy derives from the extra fat stored by the mother during pregnancy, with the average, well-nourished women losing 0.8 kg/month, so the mother needs to eat approximately 1.9MJ/day (450 kcal/day). This explains why mothers are more hungry when nursing their child than when pregnant. During lactation, there are no significant changes in BMR, efficiency of work performance, or total energy expenditure, and in most societies women resume their usual level of physical activity in the first month postpartum or soon thereafter.

Convalescent patients who need to gain weight require extra food, but the cost of this weight gain is 20-40 MJ/kg. If 1 kg is gained per month, the extra food needed amounts to approximately 1 MJ/day.

See also: Adolescents: Nutritional Requirements. Breast Feeding. Children: Nutritional Requirements. Energy: Balance. Energy Expenditure: Indirect Calorimetry. Exercise: Diet and Exercise. Infants: Nutritional Requirements. Lactation: Dietary Requirements. Obesity: Definition, Etiology and Assessment; Childhood Obesity; Complications. Pregnancy: Nutrient Requirements; Energy Requirements and Metabolic Adaptations. Protein: Requirements and Role in Diet.

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