Key Evidence:

1. The mortality risk with obesity is eliminated or largely attenuated by moderate to high levels of cardiorespiratory fitness (CRF).

2. Most cardiometabolic risk markers associated with obesity can be improved with exercise training in the absence of weight loss.

3. Intentional weight loss is not consistently associated with lower mortality risk.

4. Increasing CRF and physical activity (PA) are consistently associated with greater reductions in mortality risk than is intentional weight loss.

5. Weight cycling is associated with adverse health outcomes.

Obesity has been linked to multiple diseases and higher mortality [1-4]. Weight-loss intervention is traditionally used to treat obesity. Few have realized that weight-loss is not the only treatment available to obesity. Indeed, the high prevalence of weight-loss attempt has not been associated with reduction of obesity. Quite on the contrary, repeated weight-loss efforts may even contribute to weight gain. The phenomenon of weight cycling is associated with high health risks [5-6]. 

Cardiorespiratory fitness (CRF) and physical activity (PA) are two other alternatives to obesity treatment. 

Cardiorespiratory Fitness (CRF)

A recent review by Gaesser and Angadi [7] found strong positive health effect with higher CRF [Fig. 1]. One of the studies was a meta-analysis study by Barry et. al. [8], which showed that the mortality risk associated with high BMI was either eliminated or greatly attenuated by moderate to high levels of CRF or PA. As seen in Fig. 1, being fit has a much stronger effect in reducing the chance of mortality than weight-loss. 

In another study involving 2316 men diagnosed with diabetes, low CRF was associated with increased risk of cardiovascular mortality in all weight groups (Figure 2) [9].

Physical Activity (PA)

Certain epidemiological studies have shown that PA significantly reduces risk for all-cause mortality associated with high BMI. These studies generally showed that risk for physically active adults with obesity is comparable to, or lower than that for inactive adults without obesity [7]. However, there is no meta-analysis study so far to demonstrate the effect of PA on the BMI-mortality relationship.

A few meta-analyses of aerobic training in overweight or obese adults demonstrated reduction of visceral and liver fat, when the weight loss was frequently less than 1 kg. Although reduction in visceral fat is correlated to total weight loss, it is about 50% greater with exercise training for a given amount of weight loss compared with caloric restriction [7].

Exercise has important effects on white adipose tissues where it increases mitochondrial biogenesis, insulin sensitivity, and overall metabolic health, independent of significant weight loss.

Metabolically Healthy Obesity (MHO)

Metabolically healthy obesity (MHO) is a concept derived from clinical observations that a subgroup of obese individuals does not exhibit overt cardiometabolic abnormalities [10]. MHO individuals are characterized by lower liver and visceral fat, but higher subcutaneous leg fat, greater CRF and PA, insulin sensitivity, lower levels of inflammatory markers, and normal adipose tissue function compared to metabolically unhealthy obese (MUO) individuals. MHO still presents higher cardiometabolic disease risk than healthy lean people and is most likely a transient phenotype that requires intervention [10].

Intentional Weight Loss and Mortality

Interestingly, intentional weight loss was not associated with a lower mortality risk among healthy adults with obesity (Table 1) [7].

There have been mixed data around this topic. Overall, intentional weight loss is not consistently associated with reduced mortality risk.

Setting PA and CRF as the Goal

PA, especially if it includes moderate-to-vigorous-intensity activities, increases CRF. Obese adults have been shown to be able to increase their CRF by 1 MET or more after 8 weeks of moderate-intensity continuous or high-intensity interval training despite no body weight or body fat loss. An increase of 1 MET is associated with 14-29% lower risk of all-cause mortality and a 19% lower risk of cardiovascular disease mortality. The effect is equal to or greater than the reductions associated with weight loss [7].

Because there is a poor success rate for long-term weight-loss maintenance, it would be beneficial to shift the focus to increasing PA and CRF, using PA as more than just a tool to burn calories.

The American College of Sports Medicine (ACSM) recommends healthy adults to engage in 150-300 min of moderate-intensity, or 75-150 min of vigorous-intensity aerobic PA per week, as well as at least two times of muscle strengthening PA for all major muscle groups per week [11].

Summary

In summary, focusing on weight loss may increase anxiety and frustration as high failure rate is expected. This reduces adherence and may result in weight cycling, which leads to high health risk. 

Targeting physical activity and cardiorespiratory fitness may serve as better and more sustainable goals for obese individuals, as well as normal weight individuals for better health outcome.

References

[1] Carey, V.J., Walters, E.E., Colditz, G.A., Solomon, C.G., Willet, W.C., Rosner, B.A., Speizer, F.E., and Manson, J.E. (1997). Body Fat Distribution and Risk of Non-Insulin-dependent Diabetes Mellitus in Women: The Nurses’ Health Study. American Journal of Epidemiology 145, 614–619.

[2] Di Angelantonio, E., Bhupathiraju, S.N., Wormser, D., Gao, P., Kaptoge, S., de Gonzalez, A.B., Cairns, B.J., Huxley, R., Jackson, C.L., Joshy, G., et al. (2016). Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. The Lancet 388, 776–786.

[3] Aune, D., Sen, A., Prasad, M., Norat, T., Janszky, I., Tonstad, S., Romundstad, P., and Vatten, L.J. (2016). BMI and all cause mortality: systematic review and non-linear dose-response meta-analysis of 230 cohort studies with 3.74 million deaths among 30.3 million participants. BMJ i2156.

[4] Brown, K.F., Rumgay, H., Dunlop, C., Ryan, M., Quartly, F., Cox, A., Deas, A., Elliss-Brookes, L., Gavin, A., Hounsome, L., et al. (2018). The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br J Cancer 118, 1130–1141.

[5] Strohackerâ, K., Carpenterâ, K.C., and McFarlinâ, B.K. (2009). Consequences of Weight Cycling: An Increase in Disease Risk? Int. J. Exerc. Sci. 2, 191–201.

[6] Montani, J.-P., Viecelli, A.K., Prévot, A., and Dulloo, A.G. (2006). Weight cycling during growth and beyond as a risk factor for later cardiovascular diseases: the ‘repeated overshoot’ theory. Int J Obes 30, S58–S66.

[7] Gaesser, G.A., and Angadi, S.S. (2021). Obesity treatment: Weight loss versus increasing fitness and physical activity for reducing health risks. IScience 24, 102995.

[8] Barry, V.W., Baruth, M., Beets, M.W., Durstine, J.L., Liu, J., and Blair, S.N. (2014). Fitness vs. Fatness on All-Cause Mortality: A Meta-Analysis. Progress in Cardiovascular Diseases 56, 382–390.

[9] Church, T.S., LaMonte, M.J., Barlow, C.E., and Blair, S.N. (2005). Cardiorespiratory Fitness and Body Mass Index as Predictors of Cardiovascular Disease Mortality Among Men With Diabetes. Arch Intern Med 165, 2114.

[10] Blüher, M. (2020). Metabolically Healthy Obesity. Endocrine Reviews 41, bnaa004.

[11] American College of Sports Medicine, Physical Activity Guidelines. https://www.acsm.org/education-resources/trending-topics-resources/physical-activity-guidelines