estimate individual and group nutrient intakes with
defined confidence. J Nutr 1987;117:1638–41.
53Acheson KJ, Campbell IT, Edholm OG, Miller DS,
Stock MJ. The measurement of food and energy intake
in man-an evaluation of some techniques. Am J Clin Nutr
54Tokudome Y, Goto C, Imaeda N et al. Relative validity of a
short food frequency questionnaire for assessing nutrient
intake versus three-day weighed diet records in middle-
aged Japanese. J Epidemiol 2005;15:135–45.
55Day N, McKeown N, Wong M, Welch A, Bingham S.
Epidemiological assessment of diet: a comparison of a
7-day diary with a food frequency questionnaire using
urinary markers of nitrogen, potassium and sodium.
Int J Epidemiol 2001;30:309–17.
Published by Oxford University Press on behalf of the International Epidemiological Association
? The Author 2009; all rights reserved.
International Journal of Epidemiology 2010;209–211
Commentary: Relative importance of diet vs
physical activity for health
Eric L Ding1and Frank B Hu1,2*
1Department of Nutrition, Harvard School of Public Health, Boston, MA, USA and2Department of Epidemiology, Harvard School of
Public Health, Boston, MA, USA.
*Corresponding author. Department of Nutrition, Harvard School of Public Health, 655 Huntington Avenue, Boston, MA 02115,
USA. E-mail: email@example.com
30 July 2009
Physical inactivity and poor diet are both commonly
reported to be associated with a wide range of chronic
diseases, including hypertension, type 2 diabetes, cor-
onary heart disease (CHD) and stroke, and, together,
contribute to substantial burden of disease.1Although
it is well known that those who follow a healthy diet
also frequently have higher levels of physical activity,
which may lead to confounding, diet and physical
activity may also share and affect many common
biological disease mechanisms, such as blood pres-
sure, lipids, glucose, inflammation and adiposity.
Therefore, some questions still remain whether diet-
ary associations are (i) confounded by physical activ-
ity, (ii) causally independent of physical activity and/
or (iii) obviated by physical activity superseding
In this issue of the IJE, He ´roux et al.2conducted a
careful analysis to investigate the association of dis-
ease intermediate-derived dietary patterns and risk of
mortality, and whether such a derived dietary pattern
is associated with risk independent of physical activ-
ity. Conducted in a unique cohort comprising partici-
pants visiting an aerobic fitness centre, the authors
used reduced rank regression (RRR) on a battery of
biological intermediates—including body mass index,
blood pressure, high-density lipoprotein and total
cholesterol, triglyceride, fasting glucose, uric acid
and white blood cell levels—to derive a dietary pat-
tern score predictive of adverse levels of these inter-
mediates. They found that adverse dietary pattern
score associations were attenuated and the score
was not predictive of mortality after controlling for
self-reported physical activity and treadmill-assessed
cardiorespiratory fitness levels in particular.
The findings, at first glance, appear to suggest that
dietary associations with mortality are either con-
founded or trumped by physical activity. However,
such a conclusion should be interpreted in the context
of numerous previous epidemiological studies, where
dietary factors have been found to be associated with
risk of type 2 diabetes, CHD, stroke, cancer and mor-
tality, independent of lifestyle factors including phys-
ical activity levels.3
With a modest number of
endpoints (136 cardiovascular deaths and 445 total
deaths), statistical power of this analysis is somewhat
limited, which may explain the lack of overall signif-
icant trends between the RRR dietary pattern and
CVD and total mortality, even before adjustment for
physical activity or fitness. Conceptually, because
dietary factors may influence physical fitness directly
or indirectly through body weight, it can be argued
that dietary associations are mediated rather than
simply confounded by physical fitness.
Diet is a highly complex exposure, which can be
analysed in many ways, including macronutrient
DIETARY PATTERNS AND THE RISK OF MORTALITY