Re: fitness and health

[Guest guest]

--- In , " jwwright " <jwwright@e...>

wrote:

Hi All,

With further adieu:

Blair SN, Church TS.

The fitness, obesity, and health equation: is physical activity the

common

denominator?

JAMA. 2004 Sep 8;292(10):1232-4. No abstract available.

PMID: 15353537 [PubMed - indexed for MEDLINE]

THE MODERN LIVING ENVIRONMENT IN DEVELOPED COUN-tries

is characterized by low daily energy expendi-ture

and an abundant and inexpensive food supply,

making positive energy balance common. The re-sult

is a rightward skewing of the body mass index (BMI) dis-tribution

and an increasing prevalence of obesity.

Indisputable evidence links obesity to health problems,

including risk of cardiovascular disease, type 2 diabetes, some

cancers, and all-cause mortality.1 These associations are dose-

related,

temporally consistent, and biologically plausible,

which support a causal hypothesis. Physical inactivity also

has a dose-related, temporally consistent, and biologically

plausible relationship to the same health outcomes as those

as for obesity,2 and both obesity and inactivity have similar

patterns of association with clinical risk indicators such as

blood pressure, fasting plasma glucose, and inflammatory

markers.3-5 Furthermore, declines in average daily energy

expenditure are a likely underlying cause of the obesity

epidemic.6

However, the majority of studies examining obesity and

health have not adequately accounted for physical activity.

When physical activity has been considered, investigators

have often relied on simple self-report questionnaires in

which inaccuracy can increase proportionally with the re-spondent's

weight. Failure to adequately quantify physical

activity when examining the risks of obesity is similar to ex-ploring

risk factors for cancer and misclassifying tobacco

use. Physical activity and weight are closely linked and each

must be measured accurately and considered carefully when

examining the other.

Previous investigations, including studies from our group,

have examined the individual and joint associations of car-

diorespiratory

fitness (CRF) and body habitus to health out-comes.

Use of maximal exercise tests to quantify CRF pro-vides

an objective evaluation of an individual's recent activity

patterns and accounts for 70% to 80% of the variance in de-tailed

activity records.7 Cardiorespiratory fitness is stron-ger

than self-reported physical activity as a predictor of many

health outcomes, most likely because fitness measure-

ments are less prone to misclassification and because fac-tors

other than activity may influence both fitness and health

through related biological factors.8 For example, the age and

examination year–adjusted relative risks for all-cause mor-tality

in 1263 men with type 2 diabetes are 1.8 for inactiv-ity

but 2.9 for low fitness.9

Obese individuals with at least moderate CRF have lower

rates of cardiovascular disease (CVD) or all-cause mortal-ity

than their normal-weight but unfit peers. In fact, death

rates in the former group are about one half those of the lat-ter.

10 These results are similar whether BMI, percent body

fat, body fat mass, or waist circumference is used as the body

habitus measure 11 and are consistent for women and men 11,12

and for men with type 2 diabetes.13 These results also per-tain

to nonsmokers and after exclusion of individuals with

chronic disease or deaths within the first 5 years of follow-up.

11 Moreover, 150 minutes a week of moderate intensity

physical activity is sufficient to avoid the low-fitness cat-egory.

These results are consistent with those reported in

24 studies identified in a systematic review on physical ac-tivity,

CRF, obesity, and health.14

Two reports in this issue of JAMA examine activity and BMI

as predictors of health outcomes, with somewhat divergent

results.15,16 Wessel and colleagues 16 report that women with

low self-reported functional ability had higher risks of CVD

outcomes than women with higher levels of fitness. In con-trast,

BMI and fat distribution were not associated with CVD

risk. These findings are consistent with studies showing that

adequate levels of activity or fitness confer health benefits for

women and men in normal-weight, overweight, and obese

categories.11,13,17,18 In contrast, Weinstein and colleagues 15 re-

port

that BMI is stronger than physical activity in predicting

incident type 2 diabetes and that physical activity has little

effect on the relation of BMI to diabetes. They report signifi-cant

inverse gradients of risk across categories of physical ac-tivity

for 3 different methods of assessing activity although

the associations became nonsignificant after adjustment for

BMI in 2 of the 3 analyses.

Key questions raised by the 2 articles in this issue of JAMA

are why is the association between physical activity and in-cident

diabetes substantially reduced when adjusted for BMI

as reported by Weinstein et al 15 and why is there little evi

dence of a protective effect for activity in overweight or obese

women? And, conversely, why do Wessel et al 16 observe a

substantially lower risk for adverse CVD events in obese and

nonobese physically active women yet no association be-tween

body habitus and CVD outcomes?

Differences between these 2 studies, as well as the differ-ence

between the findings of Weinstein et al 15 and other pub-lished

work on this topic, may be due to differences among

study populations, methods, and outcomes. Wessel et al 16

followed-up women with clinical indications for coronary

angiography, whereas Weinstein et al 15 followed-up appar-ently

healthy women in the health care profession. Al-though

related, study outcomes also differed—adverse CVD

events 16 and type 2 diabetes.15 Valid assessment of habitual

physical activity is difficult. Wessel et al 16 used 2 measure-ments—

an estimate of CRF by the Duke Activity Status In-dex,

19 which was previously validated against maximal

oxygen uptake, and a self-reported physical activity ques-tionnaire.

Their results for Duke Activity Status Index are

similar to other findings for objectively measured cardio-respiratory

fitness and mortality,11-13,18 as were their results

when using the self-reported questionnaire. The 2 studies

used different measures of self-reported physical activity;

therefore, it is possible that the one used by Wessel et al is

more accurate than the one used by Weinstein et al, high-lighting

another difference in the 2 studies. The question-naire

used by Weinstein et al 15 has acceptable reliability and

shows modest correlations with other self-reported physi-cal

activity measures but apparently has not been validated

with a gold standard, such as maximal oxygen uptake or dou-bly

labeled water, as was the case for Duke Activity Status

Index.19 There are other differences in methods. Wessel et

al 16 and other recent studies 11-13,18 obtained baseline data at

a clinical examination, whereas Weinstein et al 15 did not have

such information. This may have led to greater misclassi-fication

for some variables such as the likelihood of detect-ing

subclinical disease, which could result in health status

influencing the combined associations among activity, BMI,

and incident disease.

The findings of Wessel et al 16 and Weinstein et al 15 pro-vide

a timely opportunity to examine an ongoing debate and

offer a resolution. The results presented by Weinstein et al 15

suggest that increased BMI is substantially more important

for incident diabetes, and Wessel et al 16 suggest that inac-tivity

or low fitness is a greater threat to health in terms of

CVD outcomes. In recent years, the " fitness vs fatness " is-sue

has led to controversy and heated debate. Although the

debate may never be fully resolved, the relative contribu-tion

of fitness and obesity to overall health and risk actu-ally

may be a trivial matter because a common treatment is

already available for both low fitness and excess body weight.

Increasing regular physical activity results in predictable in-creases

in fitness, and it is widely accepted that regular physi-cal

activity is a core component of successful weight loss

programs and, more importantly, of long-term weight loss

maintenance. In essence, physical activity is the common

denominator for the clinical treatment of low fitness and ex-cess

weight, making the " fitness vs fatness " debate largely

academic. Thus, physicians, researchers, and policymak-ers

should spend less energy debating the relative health im-portance

of fitness and obesity and more time focusing on

how to get sedentary individuals to become active. With 40

to 50 million adults in the United States currently not ob-taining

the recommended amount of daily physical activ-ity,

2 motivating the individuals to incorporate physical ac-tivity

into their daily lives, whether to lose weight or reduce

risk of chronic disease, will have substantial health and fi-nancial

benefits at an individual and societal level.

In summary, the majority of studies show that regular

physical activity has health benefits at any weight, and for

those who want or need to lose weight, physical activity is

a critical component of long-term weight management. Con-sequently,

physical activity promotion should be a founda-tion

of clinical therapy and public health policy, whether

to promote health or weight control. The medical commu-nity

needs to lead in communicating the importance of physi-cal

activity for health and weight maintenance. Just as weight

is addressed in some manner at nearly every physician visit,

so should attention be given to recommending the accu-mulation

of 30 minutes a day of moderate intensity physi-cal

activity at least 5 days of the week. This can be obtained

through brisk walking, bicycling, swimming, or activities

of daily life such as housework or gardening.

Cheers, Al Pater.