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You cannot outrun a bad diet has become a rallying phrase for diet-centric approaches to counteracting obesity and poor metabolic health. The phrase is, in our view, often taken to mean that you simply cannot do enough exercise to successfully lose or manage weight over time. Nonetheless, all weight loss paradigms run through energy balance,1 and the concept that you cannot outrun a bad diet is, in our view, inaccurate. Importantly, the simplicity of the phrase does not consider the multitude of other positive effects that physical activity/exercise (ie, running) have on health beyond weight loss. Evidence shows that you can out-exercise/out-work poor nutritional choices, but most people do not since they do not/will not/or cannot, practically, expend sufficient energy to do so. It is incontrovertible that exercise can and does result in weight loss.2 Nonetheless, behavioural and/or metabolic compensatory mechanisms often lessen the predicted weight loss with exercise induced as opposed to diet-induced energy deficits.2 Viewed through the lens of a weight loss approach to health, then we would agree that a dietary approach to reduce energy intake is more effective for weight loss (in the short term) and likely for maintenance of lost weight than an exercise alone approach.2 Importantly, what has been shown a number of times is that a combination of diet and physical activity betters either practice in isolation.3
While changes in dietary energy or macronutrient intake have often been cited for the rise in obesity, there is the flip side of the issue to consider: energy expenditure. Workplace energy expenditure (where we spend a large part of our day) has declined steadily.4 The impact of such a decline is hard to estimate, but it underscores that while self-reports that people are meeting the physical activity guidelines appear rosy, measured energy expended during work (for most of us the largest part of our day) are lower than in the past. Even factors as seemingly benign as neighbourhood walkability exert influence in weight gain, obesity and risk for type 2 diabetes.5
Benefits of physical activity
The other major issue with the diet-to-lose-weight-for-health paradigm is that it glosses over the health benefits of being physically active. Thus, when the sequelae of overweight and obesity are considered the evidence that being physically active contributes to reduced risk for hypertension,6 type 2 diabetes5 7 and a number of common cancers8 is staggering. It is important to note that all of these findings6–8 are observed after adjustment for body mass or body mass index. In fact, many traditional diet-related indicators of health show marked mitigation of risk even when unchanged when physical activity and fitness are considered.9
Recidivism of weight loss
Recidivism of diet-induced weight loss is also a major issue in diet-only weight loss paradigms, but here again we see that physical activity plays an important role in improving efficacy of maintaining weight loss due to dietary energy restriction.10 More importantly, self report of ‘successful’ weight loss shows considerable diversity of approaches to weight loss, but most people also report that they engage in physical activity as adjunct to promotion of weight loss and notably as a means of sustaining weight loss.1
The role of physical activity in weight loss and health
There are a number of ways to lose weight, and specific -diet-centred approaches aside, it is clear that an increased relative energy expenditure compared with energy intake is still the crux of energy balance and core to weight gain/loss.1 Evidence shows that you can ‘outrun’ poor dietary choices (a ‘bad diet’) and maintain a healthy body weight. Importantly, many physical activity-mediated benefits are not operating via traditional risk factors (ie, weight loss, blood pressure, lowering of blood lipids) and thus should not be discounted as a means contributing better health, regardless of body weight. Thus, beyond weight loss, in addition to weight loss, and even in the absence of weight loss, it is abundantly clear that being physically active is associated with a myriad of health benefits some of which are simply not achieved through diet-induced weight loss. The myriad difficulties of losing weight and maintaining weight loss need to be considered in any discussion of diet-induced weight loss and measured against any dietary approach to losing weight. In our view, the phrase that you cannot outrun a bad requires a crucial clarification and an overriding footnote, which is that physical activity can and does play a substantial role in: weight loss, weight maintenance, risk of diseases associated with obesity and health in general. We urge a continued appreciation of the role that physical activity can play in body weight management and most importantly in health and a deeper consideration of the health benefits that physical activity brings that are neither weight, weight loss, nor diet-dependent.
Contributors The article was conceived, written, verified for content and approved by both authors.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Patient consent for publication Not required.
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