A weight-neutral approach to obesity

In this narrative review, the authors proposed a weight-neutral strategy for obesity treatment, focused on increasing physical activity and cardiorespiratory fitness. Some of the authors’ conclusions should be interpreted with caution, as there were several instances in which they cited research that didn’t support their statements. Nevertheless, the general sentiment that weight-neutral interventions can effectively improve health and reduce risk for chronic disease is well-supported by the current body of literature.

This Study Summary was published on January 31, 2022.

Background

The prevalence of obesity in the U.S. has increased dramatically in the past 40 years. At the same time, more Americans are trying to lose weight,[1][2] which is consistent with other data indicating that most people who lose weight tend to gain it back.

According to the authors of the current paper, repeatedly gaining and losing weight, often called weight cycling or yo-yo dieting represents a “weight loss futile cycle,” in which the dieter wants to weigh less, attempts to lose weight, fails to reach or maintain their goal, becomes frustrated, stops trying, regains weight (sometimes more than they lost originally), wants to lose weight again, and the cycle continues.

The weight loss futile cycle

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Weight loss can certainly improve health among people with obesity. That said, a reduction in body weight is only beneficial if that new body weight is maintained. Additionally, the relationship between BMI and health isn’t as strong when controlling for other dimensions of fitness, such as physical activity (PA) and cardiorespiratory fitness (CRF). Is it possible that increasing PA and CRF without attempting to lose weight could be better for your health than a standard weight loss attempt?

The study

This narrative review sought to answer two questions:

  • What is the magnitude of mortality risk reduction associated with intentional weight loss compared to that associated with increasing either physical activity (PA) or cardiorespiratory fitness (CRF)?
  • What is the magnitude of cardiovascular disease (CVD) risk marker reduction associated with weight loss interventions compared to PA interventions?

The results

  • The BMI/mortality relationship: Influence of CRF and PA. While it’s generally assumed that a high BMI increases mortality risk, the body of literature is mixed on this topic. Some meta-analyses indeed demonstrate that a BMI of 18.5–24.9kg/m2 (the “healthy” range) is associated with the lowest mortality risk.[3][4] Other studies indicate that people with a BMI of 25-29.9 have the lowest mortality risk,[5] especially in older populations.[6][7][8] Multiple meta-analyses suggest that increased CRF, defined via maximal VO2 or VO2 peak exercise tests, attenuates[9] or eliminates[10] the association between increased BMI and mortality risk. Evidence also suggests that muscular fitness, as assessed via grip strength,[11] 1RM bench press and leg press strength,[12] or physical activity levels,[13] attenuates the association between increased BMI and mortality. However, in most of the aforementioned studies, the participants with the lowest mortality rates were physically fit and had a BMI of less than 25 or less than 30.
  • Intentional weight loss and mortality. The authors reported the results of 7 meta-analyses assessing intentional weight loss and mortality risk.[14][15][16][17][18][19][20]. The authors concluded, based on this data, that intentional weight loss is not consistently associated with reduced mortality risk. However, a more detailed look at these meta-analyses paints a different picture (see “The big picture” section at the end of this summary).

  • Weight loss via liposuction: Impact on CVD risk markers. Assessing the effects of liposuction on disease risk can help untangle whether lower levels of body fat specifically reduce disease risk. However, the authors of the current paper noted that because liposuction typically involves the removal of subcutaneous fat, most studies assessing participants who undergo the surgery cannot address the significance of ectopic or visceral abdominal fat (VAT) for cardiometabolic health. In addition, some evidence suggests that compensatory increases in abdominal fat occur after liposuction.[21]

  • Weight loss via bariatric surgery: impact on morbidity and mortality. The authors reported the results of three meta-analyses,[22][23][24] all of which found that bariatric surgery improved mortality rates. However, they cited other research indicating that blood glucose and insulin concentrations improve within days after surgery (before weight loss occurs),[25][26] that BMI trajectories after bariatric surgeries aren’t good predictors of remission and relapse of diabetes,[27] and that patient PA levels generally increase following bariatric surgery.[28][29]

  • Increasing PA or CRF: consistent reduction in mortality risk. The authors cited data from 10 cohort studies[30][31][32][33][34][35][36][37][38][39] indicating that PA reduces all-cause and CVD mortality, and 11 cohort studies[40][41][42][43][44][45][46][47][48][49][50] and one review[51] indicating that increased CRF reduces all-cause mortality. They stated that, in comparison to intentional weight loss, mortality risk reductions associated with increased PA or CRF are more consistent and of greater magnitude.

  • Does weight loss explain the reduced mortality risk associated with improvements in PA or CRF? The authors stated that weight loss contributes very little to the reduced mortality risk associated with PA and CRF. They referenced 5 studies that suggest “increasing PA results in little, if any, weight loss.”[52][53][54][55][56] Notably, one study they referenced is a position stand by the American College of Sports Medicine,[52] which indicated that “moderate-intensity PA of 150–250 minutes per week with an energy equivalent of about 1,200 to 2,000 kcal per week seems sufficient to prevent weight gain greater than 3% in most adults and may result in modest weight loss.” They also referenced a systematic review of randomized controlled trials, which found that isolated aerobic exercise interventions reduced body weight by 1.6 kg over six months, and by 1.7 kg over 12 months.[56] They also cited several studies[44][45][35][36] suggesting that the reduced mortality risk associated with increased CRF was independent of changes in BMI.

  • Pitfalls of focusing on weight loss: weight cycling. The authors noted that because many people tend to regain the weight they lose, weight cycling (repeatedly gaining and losing weight) is common. While there is debate in the literature regarding whether weight cycling poses a significant health risk, the authors cited 3 meta-analyses,[57][58][59] all of which reported increased mortality risk associated with weight cycling. Notably, one of these analyses was limited to older adults.[57] Furthermore, only one of these analyses assessed the effects of intentional vs. unintentional weight fluctuation and found that intentional weight fluctuation was not associated with all-cause mortality.[58] The authors also noted that people who experience body weight fluctuation are more likely to engage in unhealthy weight loss practices (e.g., vomiting, binge eating, and laxative use) are less likely to exercise and more likely to have a high BMI. The authors noted that weight regain following weight loss is characterized by a greater gain of fat mass compared with fat-free mass, citing three studies in support of this statement.[60][61][62] However, two of these studies reported that weight regain did not adversely affect fat-free mass [60][61] and the third was a narrative review assessing sarcopenic obesity in older adults.[62]

  • Cardiometabolic health improvement: PA vs. weight loss. The authors cited 8 meta-analyses of randomized controlled trials[63][64][65][66][67][68][69][70] indicating that weight loss interventions improve risk factors for cardiovascular disease and type 2 diabetes. However, they noted that improvements in cardiometabolic risk markers associated with weight loss are similar to exercise training interventions without a specific weight loss target. They cited evidence that exercise interventions can reduce blood pressure[71] and HbA1C[72] despite minimal changes in body weight and body fat, and that improvements in blood lipids[73] and vascular function[74] from exercise training alone are comparable to those observed in weight-loss interventions.

  • Exercise targets “unhealthy fat.” The authors cited 6 studies (they stated they were meta-analyses, however, only four of them were meta-analyses), indicating that aerobic exercise training reduces VAT and ectopic fat.[68][75][76][77][78][79] Some of these studies[75][76] reported a benefit of aerobic exercise training independent of total weight loss. Notably, one of the reviews they cited indicated that “while the benefits of exercise are apparent, from a clinical perspective, a multidisciplinary lifestyle approach with combined diet and exercise therapy is regarded as ‘best practice’ given that the strongest hepatic benefit occurs with weight loss.”[77] The authors also stated “a meta-analysis of adults with T2D demonstrated that exercise training was associated with a significant reduction in VAT despite minimal overall weight loss.”[78] However, that meta-analysis did not delineate the effect of exercise on visceral fat independent of body weight.

  • Healthy obesity phenotype: Importance of CRF and PA. The authors noted that there has been considerable debate over the metabolically healthy obese (MHO) phenotype. MHO has typically been defined as having no more than one component of metabolic syndrome, although staging systems such as the Edmonton Obesity Staging System (EOSS) and the Cardiometabolic Disease Staging System (CMDS) have been developed to stratify risks ranging from people having no obesity-related cardiometabolic disease markers to people with severe disabilities from obesity-related chronic diseases. The authors noted that that classification of MHO do not include assessments of PA and CRF, and referenced a systematic review,[80] a narrative review,[81] and meta-analysis[82] suggesting that, after accounting for physical activity, the mortality risk associated with MHO is eliminated.

  • Optimization of physical activity and CRF. The authors noted that the American Heart Association recommends measuring CRF as a vital sign in clinical practice.[83] They also noted that, because the majority of people who lose a substantial amount of weight tend to gain it back, physical activity should be encouraged as more than just a tool to produce an energy deficit.

Note

Since there were several instances in which the authors cited research that didn’t support their statements, their conclusions should be interpreted with caution. That said, the general sentiment that weight neutral interventions can effectively improve health and reduce risk for chronic disease is well-supported by the current body of literature, discussed below.

The big picture

In their review, the authors asserted that weight loss doesn’t usually improve mortality. While this was true in the main analyses, the subgroup analyses show some important caveats:

In a 2009 meta-analysis of 26 prospective studies,[15] intentional weight loss did not affect all-cause mortality. However, when stratified by baseline health and/or obesity status, that changed — intentional weight loss among “unhealthy” people reduced mortality risk by 13%. Although intentional weight loss led to a nonsignificant reduction in mortality risk (6%) among people with obesity, the effect was significant among unhealthy people with obesity (16% reduction in mortality risk).

A 2013 meta-analysis of 20 RCTs[19] assessed the effects of comprehensive lifestyle interventions in the prevention of diabetes in at-risk populations or the prevention of complications (including death) in people with type 2 diabetes, and found that such interventions reduced the risk of developing diabetes by 65%. Importantly, the authors did not explicitly state whether the interventions involved intentional weight loss.

A 2014 meta-analysis of 12 studies[18] assessed the effects of weight loss among participants with coronary artery disease on a composite outcome of all-cause mortality, cardiovascular mortality, and major adverse cardiac events, and found weight loss was associated with a 30% greater risk of the composite outcome, and when stratified by intentionality, the reduction in risk was 33%.

A 2015 meta-analysis of 15 randomized controlled trials[16] assessed the effects of intentional weight loss on all-cause mortality in adults with overweight or obesity, and found that weight loss groups experienced a 15% reduced risk for all-cause mortality.

A 2017 meta-analysis of 54 randomized controlled trials[17] assessed whether intentional weight loss interventions for adults with obesity affected all-cause, cardiovascular, or cancer mortality, as well as CVD, cancer, or body weight. Weight loss interventions reduced all-cause mortality by 18%. Furthermore, weight loss interventions reduced body weight after one, two, and more than three years.

A 2018 meta-analysis of 8 studies[14] assessed the effects of weight loss on all-cause mortality in participants with diabetes and overweight or obesity. Overall, weight loss was associated with a 15% increased risk for all-cause mortality and a 15% increased risk for CVD mortality. These results were largely driven by one study,[84] which assessed participants with pre-existing cardiovascular disease. When the authors meta-analyzed the three studies assessing intentional weight loss, there was a nonsignificant reduction in all-cause mortality.

A 2019 meta-analysis of 31 randomized controlled trials[85] assessed the effects of weight-loss interventions on weight loss over at least 1 year and associations with all-cause mortality. Body weight was lower among participants randomized to weight-loss interventions at 1 and 3 years, and these participants had nonsignificantly lower odds for all-cause mortality.

Overall, the literature cited by the authors of the current review can be summarized with a few key takeaways:

  • There is plenty of research showing that intentional weight loss is beneficial to health among people with obesity.

  • There is also research showing that achieving and maintaining weight loss is difficult, as some (but not all) people gain the weight back.[86][87]

  • Increasing CRF and PA is beneficial independent of weight loss, as this makes people decidedly healthier even if they’re not currently at an optimal body weight.

  • That said, there is also research that shows that the best outcomes occur when people with obesity both successfully achieve and maintain weight loss and increase PA and CRF.

This Study Summary was published on January 31, 2022.