Full Report - Food, Nutrition, and the Prevention of Cancer

CHAPTER 8 • DETERMINANTS OF WEIGHT GAIN, OVERWEIGHT, AND OBESITY
plausible mechanisms by which dietary fat could lead to positive
energy balance and obesity. The efficiency of nutrient
use is higher for fat than carbohydrate or protein. When
energy balance is positive and fat is being stored, the storage
of this fat only requires a small degree of oxidation
(approximately 3 per cent of the energy stored). The high
energy density of fat may promote passive overconsumption.
Prolonged consumption of a high-fat diet may desensitise the
individual to a number of appetite controls. The palatability
of fat may induce voluntary overconsumption.
The evidence on animal fats is assessed here as a
marker for energy-dense foods. For this reason, no
separate judgement is made for animal fats.
High energy-dense foods are probably a cause of
weight gain, overweight, and obesity, particularly
when large portion sizes are consumed regularly. They
have this effect by promoting excess energy intake.
Also see entries on sugary drinks (8.8.6), ‘fast foods’
(8.8.7), and television viewing (8.8.8).
The Panel is aware that since the conclusion of the SLR, one
cohort 219 and one case-control study 180 have been published.
This new information does not change the Panel judgement (see
box 3.8).
8.8.6 Sugary drinks
The evidence on sugary drinks is reviewed separately due to
its independent effect on body fatness. It also contributes to
the judgement on energy-dense foods and drinks.
One RCT220 and four cohort studies investigated sugary
drinks. 115 221-223 Two cohort studies were in adults115 223 ; the
trial and two other cohort studies were in children.
221 222
The single trial included 644 children randomised by class
to receive teaching sessions to discourage consumption of
sugary, carbonated drinks or to control. After 12 months,
change in BMI z-score was non-significantly lower in the
intervention group, with a change of 0.7 (SD 0.2) compared
with 0.8 (SD 0.3) in the control group. 220
Three cohort studies showed increased risk of weight gain
when frequency of sugary drink intake increased,
115 222 223
which was statistically significant in two. 115 222 One study
showed no association. 221 This study was in children, and
investigated intake of ‘fruit drinks’, but excluded fruit juice,
soda (fizzy drinks), or diet soda. The effect estimates for the
two adult studies were mean weight gain of 4.69 kg for 1991
to 1995 and 4.20 kg for 1995 to 1999 in women who
increased their sugar-sweetened soft drink consumption, and
1.34 kg and 0.15 kg in women who decreased their consumption
223 ; regression coefficients of 0.20 (p value for trend
< 0.01) for the univariate model relating weight gain to
increase in intake of sugar-sweetened soft drinks and 0.12
(p value for trend 0.05) for the multivariable model (this
study also reported a statistically significant relationship with
increased waist circumference). 115 The cohort study in children
that reported an effect estimate showed that BMI
increased by 0.24 kg/m 2 (95% CI 0.10–0.30; p value for
trend 0.03) per sugary drink (not including fruit juice)/day
and the effect estimate for the frequency of obesity was 1.60
(95% CI 1.14–2.24; p value for trend 0.02), also per drink/
day. 222
There is considerable variation in the definition of ‘sugary
drinks’ between studies. The study that reported no association
excluded fizzy drinks.
Studies have demonstrated that, when consumed as part
of a soft drink, the energy from sugars may not be compensated
for in the same way as when consumed as part of a
solid meal. 224 Limited studies have shown that in adults,
short-term (10-week) intake of sugar-sweetened foods and
drinks (of which 80% were drinks) promoted weight gain,
whilst consumption of artificially sweetened foods resulted
in weight loss. 28
The epidemiological and mechanistic evidence that
drinks containing added sugars, including sucrose and
high-fructose corn syrup, are a cause of weight gain,
overweight, and obesity is substantial and consistent.
Sugary drinks probably cause weight gain, overweight,
and obesity. Like energy-dense foods and drinks, they
have this effect by promoting excess energy intake.
The Panel is aware that since the conclusion of the SLR, one
RCT, 225 one cohort, 226 and one case-control study 180 have been
published. This new information does not change the Panel
judgement (see box 3.8).
8.8.7 ‘Fast foods’
The evidence on ‘fast foods’ is reviewed separately due to
their independent effect on body fatness. It also contributes
to the judgement on energy-dense foods and drinks.
Six cohort studies investigated ‘fast foods’ (see box 8.2),
four in adults and two in children.
165 227-231
All six cohort studies showed increased risk of weight gain
with increased intake of ‘fast foods’, which was statistically
significant in four, 165 227 229 230 and in women but not men in
an additional study. 231 Effect estimates in adults were a
regression coefficient of 0.85 (95% CI 0.43–1.27; p value for
trend < 0.05) in low-income women and 0.39 (95% CI
0.15–0.64; p value for trend < 0.05) for the association
between number of ‘fast-food meals’ per week and BMI 231 ;
a 0.85 (95% CI 0.75–0.96) chance of maintaining weight
(equivalent to a 15 per cent increased risk of weight gain) 165 ;
a weight gain of 1.72 kg (95% CI 0.52–2.92; p value for
trend 0.005) greater for black people who visited ‘fast-food
restaurants’ frequently compared to those who visited infrequently,
and 1.84 kg (95% CI 0.86–2.82; p value for trend
< 0.0013) greater for the same comparison in white people
230 ; and a 0.72 kg (95% CI 0.33–1.11; p value for trend
< 0.01) greater weight gain for people who visited fast-food
restaurants more than twice a week compared to those who
visited infrequently. 229 One study in children showed a statistically
significant greater increase in BMI z-scores of 0.82
for those who ate food from quick-service outlets more than
twice a week compared to 0.28 for those who never ate
quick-service foods (p value for trend 0.0023). 227 One study
in children stated that there was a statistically significant
association between increased ‘takeaway food’ intake and
BMI at the age of 8, but that after multivariable adjustment
339