In 2017–2018, 42.4 percent of adults in the United States were obese, up from 30.5 percent in 1999–2000, according to the Centers for Disease Control and Prevention (CDC).
Obesity rates have risen in tandem with an increase in persons striving to reduce weight. However, the calorie restriction required for weight loss can be difficult to maintain for an extended period of time.
Furthermore, many people are unable to reach their ideal weight, and those who do are frequently unable to maintain it.
Both of these scenarios can lead to frustration and a lack of commitment to the weight-reduction program, resulting in a cycle of weight gain and loss. Weight cycling is a term for this type of weight fluctuation, which has been linked to negative health outcomes.
The rapid rise in obesity rates, despite a greater emphasis on weight loss, demonstrates the limitations of this weight-loss-focused approach to obesity management. Despite this, obesity management recommendations continue to promote the practices of calorie restriction and increased physical activity.
Some scientists have argued during the last two decades that a weight-loss-focused strategy to obesity care may be misguided. Instead, they recommend that those who want to lose weight focus on a "fat-but-fit" approach that includes increasing physical activity and boosting cardiorespiratory fitness.
Advocates of the fat-but-fit approach to obesity therapy say that boosting fitness can help reduce the risk of cardiovascular disease and mortality even if weight loss is not achieved.
Cardiorespiratory fitness is a measure of overall physical fitness, while physical activity refers to any movement that results in energy expenditure. The ability of the circulatory and respiratory systems to sustain physical exercise for an extended amount of time is measured by cardiorespiratory fitness.
Now, a study published in the journal iScience examines how to lower the risk of obesity-related health problems and mortality. It compares the efficacy of physical activity and cardiorespiratory fitness to the success of weight loss.
According to the evidence presented in the study, the fat-but-fit method may be just as beneficial as weight loss in reducing the risk of cardiovascular disease and mortality associated with obesity. Furthermore, by focusing on fitness rather than weight loss, this plan avoids the drawbacks of the weight loss approach.
Body mass index and mortality risk
Doctors use the body mass index (BMI), which is the ratio of a person's weight to the square of their height, to determine if they are overweight or obese.
People with a BMI of greater than 25 kg/m2 but less than 30 kg/m2 are overweight, whereas those with a BMI of 30 kg/m2 or more are obese, according to the conventional classifications.
Although some studies demonstrate that those with a BMI of more than 25 kg/m2 had a higher risk of death, others contradict these findings, according to the authors of the current study.
According to some of the research, those who have a BMI in the overweight range have a reduced mortality risk than people who have a BMI in the healthy range, which is between 18.5 and 24.9 kg/m2. Furthermore, one of the research found that those who are obese do not have a higher mortality risk than people who are of a "healthy" weight.
Weight loss and mortality risk
While some studies demonstrate that purposeful weight loss through calorie restriction and physical activity can reduce mortality risk, others show that weight loss and mortality risk are unrelated.
To put it another way, research hasn't consistently demonstrated that losing weight lowers mortality risk.
The most common weight-loss advice is to decrease calorie intake while increasing physical exercise. As a result, studies claiming a reduction in mortality risk related with weight loss may be attributing this finding to an increase in physical activity rather than weight loss itself.
The authors of the new study also point out that maintaining weight loss over time can be difficult. Weight cycling has become more common as more people try to reduce weight by limiting their calorie consumption.
Weight cycling is linked to an increased risk of cardiovascular disease-related and all-cause death, according to three recent meta-analyses.
Dr. Glenn Gaesser, an Arizona State University professor and co-author of the study, was questioned by Medical News Today if hazardous practices like excessive calorie restriction could explain the limited advantages of weight loss in obese people.
According to Dr. Gaesser:“Unhealthy weight loss practices are much more common among persons with a high BMI who also attempt weight loss more frequently. We contend that it is entirely plausible that [many] of the health risks associated with obesity are due to the adverse effects of weight cycling. Weight cycling is associated with increased mortality risk, and weight cycling is more prevalent among persons with obesity.”
Fitness and mortality risk
Unlike weight loss, there is stronger evidence that cardiorespiratory fitness can significantly reduce or even eliminate the mortality risks associated with a high BMI.
For instance, consider a meta-analysis. According , cardiorespiratory fitness can dramatically reduce the risk of all-cause and cardiovascular disease-related mortality in people with a high BMI. Furthermore, fit people with excess body weight had a reduced risk of death from any cause than unfit people with a healthy weight.
Physical activity can also reduce the risk of all-cause and cardiovascular disease-related mortality that comes with a high BMI. Physical activity, on the other hand, has a smaller impact on mortality risk than cardiorespiratory fitness.
Increased physical activity and improved cardiorespiratory fitness can also reduce the mortality risk linked with BMI in the long run, according to follow-up studies.
Furthermore, gains in cardiorespiratory fitness and physical activity are associated with a lower risk of death than weight loss.
Notably, several of these studies found that the benefits of physical exercise and enhanced cardiorespiratory fitness were accompanied by either minor or no weight loss. This means that the lower all-cause and cardiovascular disease-related mortality risk linked with greater exercise cannot be attributed to weight loss.
Cardiometabolic markers
Improvements in indicators for obesity-related disorders, such as cardiovascular disease and type 2 diabetes, can also be achieved by increased physical activity and cardiorespiratory fitness. These changes in cardiometabolic indicators are similar to those seen with weight loss.
According to the authors of the current study, both resistance training and aerobic exercise lower blood pressure, with the magnitude of the fall comparable to that seen with weight loss.
Similar to weight loss, exercise training increases blood glucose control, blood cholesterol levels, and vascular function. Weight loss had no effect on the benefits of exercise training on the aforementioned cardiometabolic indicators.
Exercise training can also help you lose weight by reducing the amount of fat stored in your liver and visceral adipose tissue. The fat that surrounds internal organs, particularly in the belly, is known as visceral adipose tissue.
A higher risk of cardiovascular disease and type 2 diabetes is linked to fat accumulation in the liver and visceral adipose tissue.
While the amount of fat stored in the liver and visceral adipose tissue tends to correspond with the amount of weight lost, exercise training can result in a clinically significant reduction in fat reserves in the liver and visceral adipose tissue even if weight loss is not achieved.
While extreme calorie restriction is more successful than exercise training in lowering fat reserves, the authors point out that calorie restriction for lengthy periods of time is not often sustainable.
Reduced insulin sensitivity of fat tissue occurs in obesity and type 2 diabetes, and exercise training can increase fat tissue's response to insulin.
Implications
For obesity management, the authors advocate a weight-neutral approach that focuses on improving cardiorespiratory fitness and boosting physical activity.
While healthcare providers should not discourage weight loss, it should not be the major emphasis of obesity management, according to the authors.
According to Dr. Gaesser, “Current obesity treatment guidelines do not even mention ‘fitness’ and only encourage physical activity as a means to facilitate weight loss. This approach ignores the major improvements in mortality and disease risk associated with increased physical activity and improved fitness in the absence of weight loss. In fact, as our review shows, improving fitness by increasing physical activity is associated with greater reductions in mortality risk compared to weight loss.“
“So, if the goal of obesity treatment is to improve health and longevity prospects, it seems only logical that improving fitness should be emphasized more than weight loss. We would like to see current physical activity guidelines be an important focus of obesity treatment programs, with cardiorespiratory fitness assessed and monitored over time to document improvements in fitness.”
- Dr. Glenn Gaesser
“Fitness should be included as an essential ‘vital sign’ for assessing a person’s health status. Although we focus on obesity in this review, it is important to highlight the fact that fitness impacts health and longevity prospects for everyone, regardless of body weight,” added Dr. Gaesser.
Challenges
Dr. Jennifer Kuk, an associate professor at York University in Canada, spoke with MNT about the difficulties in determining the specific impact of fitness in obesity-related health problems.
According to Dr. Kuk,“Unlike body weight, which is a very simple measure that is also often done by self-report, fitness requires an exercise test, wherein the gold standard is a maximal exercise test. This is expensive [and] time- and labor-intensive for both the researcher and participant.”
“Physical activity is most often done by self-report, but often associations between activity and health are not as strong as what is observed with fitness. Physical activity and fitness do not always track, as there is a genetic component that will dictate your ability to increase your fitness with activity. Further, there may be recall errors in self-report issues, which would make it more difficult to see the true relationship between activity and health.”
The authors of the study and Dr. Kuk both observed that only a limited percentage of people may be classified as overweight yet fit, making it difficult to study the link between fitness and obesity-related health problems. There are also issues with the absence of defined standards for determining whether a person with a certain BMI and fitness test score (VO2 max) is fit or unfit.
“[Another] issue is that with physical activity and fitness, there may be an effect of reverse causality. Is your fitness or activity level reflective of your health or the reverse (i.e., you are less active and fit because you are sick vs. you get sick because you are less active and fit)?,” said Dr. Kuk.
“This is particularly important given that the largest gains in mortality risk reduction are associated with even modest amounts of physical activity, often far lower than what is recommended in the physical activity guidelines.”
Caveats and qualifications
The need of boosting fitness levels for the management of obesity, as advocated by the fat-but-fit method, is well acknowledged. However, the scientific and medical communities are concerned about the emphasis placed on weight loss and other obesity-related problems.
Dr. Jennifer Bea, a proponent of a multifaceted, nuanced approach to obesity management, told MNT: “Physical activity has been shown to improve health independent of weight loss. One of the ways in which physical activity influences cardiometabolic health is by improving body composition, i.e., increasing skeletal muscle mass and reducing adipose.”
“BMI, which is used to classify overweight and obesity in the U.S. and other places, is not a direct measure of body composition […]. Of course, physical activity also improves cardiovascular fitness, which is also risk-reducing.”
“However, it is important to recognize that obesity is a multidimensional health issue with multifactorial contributors. Thus, being physically active is not a license to maintain a poor diet or to ignore other contributors to obesity. Other contributors to obesity may include issues with sleep, certain medications, the microbiome, and many more.”
– Dr. Jennifer Bea
Dr. Bea continued: “We must not forget about individuals that are considered normal weight either. Poor body composition among those with a ‘normal BMI’ has also been associated with p
oor cardiometabolic biomarkers and health risks.”
“While there is minimal risk in advocating for increased physical activity across weight categories when following the [American College of Sports Medicine (ACSM)] guidelines for physical activity testing and prescription, it would behoove us to move beyond BMI to a more comprehensive evaluation of risk factors to at least include body composition, physical activity, blood pressure, and blood biomarkers.”
Dr. Bea is a member of the ACSM and an associate professor of medicine at the University of Arizona Health Sciences.
Dr. Kuk made a similar observation.: “In the end, I think there is consensus that fitness and physical activity is beneficial, and obesity is deleterious to health. Focusing solely on one at the detriment of the other factor is likely not a wise approach.”
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