Environmental Engineering Reference
In-Depth Information
74% of boys and 86% of girls in these studies were from
affluent Western countries, and all individuals from low-
income countries were from just five countries in Latin
America: the set had no entries from Asia or Africa, con-
tinents that contained nearly 75% of the world's popula-
tion in 2005. But no uncertainty is more intriguing that
the highly variable energy cost of pregnancy. The latest
consensus advice for pregnant women is to add just 0.35
MJ/day during the first trimester, 1.5 MJ/day during
the second, and 2.0 MJ/day during the third, and well-
nourished lactating women should increase food intake
by 2.1 MJ/day (FAO 2004). In low-income countries,
where smaller women give birth to smaller babies, the
costs should be lower but, astonishingly, several sets
of detailed energy balance studies show that many
women have, not as exceptional individuals but as
groups, extremely low energy needs during pregnancy
and lactation.
Prentice (1984) found that, compared to standard
metabolic expectations, pregnant rural Gambian women
appeared to have energy shortfalls of at least 600 kJ and
as much as 2.15 MJ/day, even if they just slept, ate, and
rested. But they not only worked hard but often engaged
in tasks that would not be contemplated by most West-
ern women, so their daily energy shortfalls would be
up to 2.50-4.14 MJ/day when performing their duties.
Adair and Pollitt (1982) found a similar situation in
Taiwanese mothers giving birth to healthy children. And
Norgan, Ferro-Luzzi, and Durnin (1974) found that
among the Kauls of New Guinea there was no difference
in energy intakes of nonpregnant and nonlactating
women and pregnant and lactating women.
Not only pregnant women but whole populations have
been shown to live with surprisingly low food energy
intakes. Among the Senegalese, Ferlo proved that a large
seasonal food deficit (nearly 1.25 MJ/day compared to
standard recommendations) was not accompanied by any
significant increase in malnutrition or any clinical signs of
food deficiency (Benefice, Chevassus-Agnes, and Barral
1984). And in New Guinea the average energy intakes
of the whole coastal Kaul tribe were just 27% (males)
and 13% (females) higher than their expected basal meta-
bolic rates, or about 2.4 MJ/day less for men and 2.9
MJ/day less for women than in a highland village, dis-
parities unexplainable by differences in methodology
(identical techniques were used), body weights,
food
availability, or work.
Given the large variability of adult BMRs (see section
5.1), recommended energy intakes based on BMR
regressions have a high degree of uncertainty when ap-
plied to individuals. Looking back in 1983, Elise Wid-
dowson, a pioneer of modern nutritional studies, noted
that the fundamental question she had posed in the late
1940s—Why can one person live on half the calories of
another and yet remain a perfectly efficient physical
machine?—has never been satisfactorily answered (Wid-
dowson 1983). This is still true a generation later; the
difference must come down to metabolic efficiencies, and
there is little doubt that not only some exceptional indi-
viduals but entire populations can use food energy much
more efficiently than the standard expectations would
have it. Such adaptations as reduced activity, weight loss,
or lower milk production would be obviously undesir-
able, but evidence of harmless adaptations means that
there is a range of long-term averages of energy intakes
compatible with regulation of expenditures without
exceeding the homeostatic limits.
Such conclusions are particularly noteworthy given
the post-1980 epidemic of obesity in North America
(and to lesser extent elsewhere), and growing indications