Physical inactivity makes you fat, right? Most people on the street would probably agree with this supposition; popular science contends that lack of exercise means lower caloric expenditure, which translates to weight gain unless we reduce caloric intake. If we then inquire about why obese individuals tend to exercise less (on average) than leaner folks, many respondents would attribute the difference to laziness, lack of willpower, and less discipline among the former.
These answers all align with a deeply ingrained conventional wisdom regarding exercise and obesity; they rest upon the assumption that Physical Activity Levels (PALs) exist in a unidirectional relationship with the development of obesity: physical inactivity as cause of obesity, not an effect/consequence.
But is this actually true?
A Chicken-and-Egg Situation
Some studies clearly associate obesity with physical inactivity. Many people thus assume that physical inactivity causes weight gain and obesity, a seemingly logical conclusion.
A critical caveat, however, is that these studies don’t establish a cause-effect relationship; they only correlate two variables. In other words, physical inactivity might be an effect of obesity, not a cause, or perhaps it is both cause and effect. It could also be that confounding variables skew the relationship, creating a false appearance of causality. Since there are so many factors to consider, it’s important to be cautious when we interpret results of any such studies.
That said, physical activity and body-fat regulation are connected. Indeed, there is solid evidence to show that physical inactivity can contribute to weight gain, though it alone is insufficient to induce obesity. Combined with other factors such as a highly processed diet and disordered sleep, it can certainly contribute to a body mass index that exceeds 30, the AMA-established definition of obesity.
The weight of the evidence from systematic reviews and meta-analyses suggests that exercise alone doesn’t produce a lot of weight loss (though people respond variably). This isn’t necessarily surprising, given that many exercisers compensate for their exertions by eating more and/or being more sedentary outside the exercise period.
However, exercise is still highly beneficial, metabolically. Regular exercise can help improve leptin and insulin sensitivity, increase lean muscle mass, improve appetite regulation, and elevate resting energy expenditure, among other effects. It is therefore unsurprising that several studies have found exercise helpful in the prevention of obesity.
A Case of Reverse Causality?
As explained above, evidence indicates that physical inactivity can factor into weight gain. However, it can proceed in the other direction as well; physical inactivity can actually derive from the accumulation of excess body fat.
This may seem counterintuitive to many people. Common public perception holds that some people exercise more than others simply because they possess more willpower and self-discipline, and that it is unrelated to their physiology.
This simplistic belief has caused many overweight and inactive people much suffering, since they may assign their inactivity to some imagined laziness or weak-mindedness. This self-labeling can then feed into poor self-confidence and depression, particularly if they hear other (often leaner) people criticizing their perceived lassitude.
Let’s be clear: willpower and self-discipline are fundamental to long-term adherence to an active lifestyle. However, a truth that eludes many folks is that these qualities aren’t fixed traits determined by genetic lottery; they can be learned and strengthened.
Furthermore, the human ability and desire to be active, as well as the enjoyment we derive from it, are governed by biological as well as psychological factors. I have learned that a key reason many obese people find exercise overly difficult and strenuous is that they are often chronically inflamed, with compromised immunity and metabolism.
Chronic Fatigue, Physical Inactivity, Suboptimal Physical Performance: Is Inflammation the Culprit?
Obesity is partly characterized by elevated levels of circulating inflammatory cytokines, a state of chronic, low-grade, systemic inflammation. Obesity is recognized as one cause of this inflammatory state, given that fat tissue releases many inflammatory mediators.
However, this internal fire can also be a cause of obesity. Inflammation and disruption of microbial balance—resulting from factors such as antibiotic use, a highly processed diet, and translocation of bacterial endotoxins from the gut into the bloodstream—may themselves cause insulin and leptin resistance, impaired appetite regulation, cravings for unhealthy foods, overeating, and fat accumulation. It’s a vicious cycle in which a perturbation of gut flora and immune homeostasis leads to excessive caloric intake and fat gain, which then further exacerbate the inflammatory process.
When the body is systemically inflamed, it doesn’t prioritize reproduction or peak physical fitness; rather, it allocates resources to damage control. It doesn’t “want” to run, lift heavy things, or perform other musculoskeletally demanding activities; it prefers rest, so it has a chance to recuperate. Chronic, low-grade inflammation is tightly linked with chronic fatigue and many other conditions that impair our physical performance and exercise tolerance.
Unfortunately, with obesity, the inflammatory cascade never stops. Fat tissue keeps pumping out TNF-alpha and other cytokines, and lipopolysaccharide continues to leak from the gut into the bloodstream, unless we undertake dietary changes and rebalance the microbiome. Until we address the inflammation, physical activity will continue to be low-priority—and gym time may continue to feel like purgatory.
Another caveat: although many lines of evidence implicate the inflammatory processes described above, other yet-unidentified factors and mechanisms may be involved. Regardless, many obese people—and non-obese people with chronic inflammation—have great difficulty getting active.
Exercise Shouldn’t Feel Like Torture
I was a strength coach and personal trainer at a commercial gym for several years. During this period I spent quite a bit of time observing how people exercise, as well as their body language and the feelings they expressed when they were lifting weights, running, or otherwise engaging their muscles. I noticed that high levels of adiposity seemed to make exercise much harder for some people.
For some, a session on the treadmill looks like pure torture. Of course, this might be due partly to the discomfort of carrying excess weight; however, I think the aforementioned processes of inflammation and hormonal disturbance are the real culprits.
Keep in mind that chronic, systemic inflammation doesn’t only affect obese people. Actually, this condition is rampant in our society today, and is at the root of many chronic diseases and health conditions. Even lean people, if inflamed, may be exercise-intolerant. Personally, my urge to exercise, as well as my physical performance, seem to vary with the levels of inflammation in my body.
A New Understanding of an Old Problem
Many studies have investigated the relationship between PALs and obesity; again, though, many fail to prove that one variable precedes the other. However, some researchers have been able to connect the two in a causal way.
One example is a study out of the University of California, Los Angeles that was published in the journal Physiology & Behavior. In the study, 32 female rats were allowed ad libitum access to unrefined rodent chow or a purified low-fat diet. After six months, the rats on the purified low-fat diet, which was rich in sugar and highly processed, had gained significantly more weight than the rats on the diet of unrefined rodent chow.
The researchers tested the rats’ performance by requiring them to press a lever to receive a food or water reward; they found that the rats on the junk-food diet demonstrated impaired performance, taking substantially longer breaks than the lean rats before returning to the task. During a 30-minute session, the overweight rats took breaks nearly twice as long as those taken by the lean animals.
Lead researcher Aaron Blaisdell, in a press statement, framed the study results as follows:
““Overweight people often get stigmatized as lazy and lacking discipline,” Blaisdell said. “We interpret our results as suggesting that the idea commonly portrayed in the media that people become fat because they are lazy is wrong. Our data suggest that diet-induced obesity is a cause, rather than an effect, of laziness. Either the highly processed diet causes fatigue or the diet causes obesity, which causes fatigue.”
Blaisdell believes the findings are very likely to apply to humans, whose physiological systems are similar to rats’.”
Key Points
Obesity can be both a cause and a consequence of physical inactivity. Physical inactivity can contribute to weight gain; combined with other factors, it can create obesity, as it down-regulates the sensitivity of metabolic and satiety-related hormones, sacrifices lean tissue, and reduces energy expenditure, among other effects. Physical inactivity can also be an effect of obesity, if accompanying inflammation and metabolic disruption lead to chronic fatigue, muscle weakness, impaired physical performance, and poor exercise tolerance.
It’s a vicious cycle: physical inactivity contributing to fat accumulation, leading to (possibly) excess body weight and secretion of inflammatory cytokines, both of which may drive further reduction in physical activity levels.
The next time you encounter an obese person who seems to find exercise difficult and unpleasant, avoid judging them. They may be fighting a decidedly uphill battle, with their biochemistry stacked against them.
Reference
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source https://paleomagonline.com/obesity-a-cause-or-a-consequence-of-physical-inactivity/
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