The importance of fat-free mass as the key determinant of resting metabolic rate, even in a very obese individual [sic], cannot be over emphasized. Obese individuals [sic] can present with wide variations in lean body mass, almost entirely accounted for by differences in skeletal muscle mass. Thus, any change in muscle mass can markedly affect basal energy requirements. In this context it is important to remember that in ambulatory individuals, the mass of weight‐bearing muscles is directly proportional to BMI, as heavier individuals require a greater skeletal muscle mass to support and move their excess weight. This alone accounts for much of the higher basal and activity‐related energy requirements of larger individuals.
Although inactivity may be the most common cause of decreased skeletal muscle mass and reduced basal metabolic needs in obese individuals [sic], it is important to consider other causes of muscular atrophy that can likewise markedly reduce energy demands. A wide range of nutritional, neuromuscular, endocrine, renal, cardiac, pulmonary, inflammatory, infectious or neoplastic conditions can result in muscular wasting and sarcopenia. Reduced skeletal muscle mass and weight gain is also noted after many cancer treatments, although the mechanisms remain unclear. Any reduction in skeletal muscle mass not accounted for by a decrease in physical activity and ambulation should prompt investigations for other causes of muscular wasting.
Commentary: Sarcopenic obesity is perhaps even more prevalent than most people may think – especially in people who have slight overweight or even moderate obesity. It is particularly common in certain ethnic groups such as South Asians, even at “normal” BMIs. Clinically, this is where body composition studies can be helpful. Although a reduction in muscle mass does reduce resting metabolic rate (RMR), it is important to remember that overall skeletal muscle only accounts for about 15% of RMR. This is why, the notion that building up muscle mass will help with weight loss by burning more calories is not really an effective weight loss strategy.
In the same manner in which a complete understanding of oedema requires the assessment of the complex physiological systems affecting fluid and sodium homeostasis, understanding obesity requires a comprehensive appreciation of the multitude of factors affecting energy intake and expenditure. Energy expenditure can be further subdivided into non‐activity (= resting metabolic rate + dietary‐induced thermogenesis) and activity thermogenesis (= non‐exercise + exercise activity thermogenesis). For simplicity’s sake, these three elements can be termed diet, metabolism and activity. A change in any one of these elements, if not balanced by corrective changes in the others, will result in a net change in energy balance, which, if positive, will result in caloric ‘retention’ and weight gain.
In subsequent posts, I will discuss the many factors that can affect energy metabolism, food intake, and physical activity and how changes to each (if not balance by corrective changes in the others) can lead to weight gain and often pose barriers to obesity management.
Several years ago, my colleague Raj Padwal and I published a paper in Obesity Reviews, where we outline a rational approach to an aetiological assessment of obesity.
As many readers may not have seen this paper, I will repost several of the key elements we discussed in it. Although some of our thinking has evolved since then, I believe the overall reasoning remain as relevant today, as when we first wrote the paper back in 2010:
Obesity is characterized by the accumulation of excess body fat and can be conceptualized as the physical manifestation of chronic energy excess. Using the analogy of oedema, which is the consequence of positive fluid balance or fluid retention, obesity can be seen as the consequence of positive energy balance or caloric retention. Just as the positive fluid balance of oedema can result from a host of underlying aetiologies including cardiac, hepatic, renal, endocrine, infectious, venous, lymphatic or drug‐related causes, obesity can result from a wide range of aetiologies that promote positive energy balance.
As with oedema, assessment and management of obesity requires an exploration of the root causes and underlying pathologies. To extend the obesity–oedema analogy, addressing all forms of obesity simply with caloric restriction and exercise (‘eat less and move more’) would be akin to addressing all forms of oedema simply with fluid restriction and diuretics. As this narrowly focused approach is not considered standard‐of‐care in managing patients with oedema, why should it be considered as the preferred method of treating obesity?
The classical treatment of obesity, based on increased physical activity and decreased calorie intake, has not been successful. Approximately two‐thirds of the people who lose weight will regain it within 1 year, and almost all of them within 5 years. In our opinion, the lack of efficiency in these therapeutic approaches is likely due to an incomplete understanding of the precise aetiology or aetiologies of obesity and, consequently a failure to address the root causes of energy imbalance.
In this paper, we present a theoretical diagnostic paradigm that provides an aetiological framework for the systematic assessment of obesity and discuss how this framework can enhance our ability to diagnose and manage obesity in clinical practice. The framework considers socio‐cultural, physiological, biomedical, psychological and iatrogenic factors that can determine energy input, metabolism and expenditure.
Comment: In hindsight, I would note that apart from failure to address the underlying pathology and drivers of weight gain, the “failure’ of conventional “eat-less – move-more” approaches to obesity management, relying largely on willpower, primarily fail because these efforts are counteracted by powerful neuroendocrine factors that both defend against continuing weight loss and promote weight regain. At the time we wrote this paper, we had perhaps not given the powerful nature of these effects full consideration. Nevertheless, I still believe that trying to understand exactly why a given person has gained excess weight is a good start to any obesity management endeavour.
More to follow…
I was recently, once again asked about my opinion on weight-loss challenges. So here is a repost of an article I wrote back in 2008 on this topic – apparently, it is still as relevant today, as it was almost a decade ago.
There appears to be a rather widespread notion out there that introducing a bit of competition into the affair may spurn people on to try and lose those “extra” pounds.
In fact, a quick google search on the term “weight-loss challenge” reveals an amazing array of challenges from voyeuristic and sadistic TV shows like the “Biggest Loser” to well-meant workplace wellness initiatives or fund raisers. I am sorry to admit that I recently even became aware of a weight-loss challenge within my own hospital – well intended, but useless in the fight against obesity.
So what’s wrong with this idea? Isn’t competition a great motivator?
Sure it is – and people will do anything to win a competition – including crazy stuff like starve themselves, exercise till they drop, or even (God forbid) pop diet pills, diuretics or laxatives just to win.
All of this is in direct contradiction to a fundamental principle of obesity management: you do not do things to lose weight that you are unlikely to continue doing to keep the weight off.
Most people seem to think that if only they could lose some weight, they will somehow be able maintain that lower body weight in the long-term with less effort.
The reality unfortunately is (and most dieters have experienced this over and over again) that no matter what diet or exercise routine you chose, no matter how slow or fast you lose the weight, no matter how long you keep the weight off – the minute you relax your efforts, the weight simply comes back.
As I have blogged before: obesity is a chronic disease for which we have no cure – only treatments! When you stop the treatment the weight (and any related problem) simply comes back.
By now you will already have figured out the problem with these challenges – unless you are very modest and reasonable about your weight-loss target and are carefully making changes that you can reasonably sustain forever, you are simply setting yourself up for failure.
If you are indeed modest and reasonable – you’ve already lost the competition to all the crazy folks who’ll do anything just to win.
My advise to anyone with a weight problem – the next time you see an invitation to a weight-loss challenge – simply ignore it!
If you really think you will benefit from obesity treatment – seek help from a trained and accredited health professional with experience in weight management – let’s put an end to weight cycling!
Regular readers will be quite familiar with the findings that cardiometabolic health appears to be far more related to “fitness” than to “fatness” – in other words, it is quite possible to mitigate the metabolic risks commonly associated with excess body fat by improving cardiorespiratory fitness.
Now, a study by Kathy Do and colleagues from York University, Toronto, published in BMC Obesity, shows that this relationship also holds for people with quite severe obesity.
The researcher studied 853 patients from the Wharton Medical Clinics in the Greater Toronto Area, who completed a clinical examination and maximal treadmill test. Patients were then categorized into fit and unfit based on age- and sex-categories and in terms of fatness based on BMI class.
Within the sample, 41% of participants with mild obesity (BMI<35) had high fitness whereas only 25% and 11% of the participants with moderate (BMI 35-40) and severe obesity (BMI>40), respectively, had high fitness.
Individuals with higher fitness tended to be younger and more likely to be female.
While overall fitness did not appear to be independently associated with most of the metabolic risk factors (except systolic blood pressure and triglycerides), the effect of fitness in patients with severe obesity was more pronounced. Thus, the prevalent relative risk for pre-clinical hypertension, hypertriglyceridemia and hypoalphalipoproteinemia and pre-diabetes was only elevated in the unfit moderate and severe obesity groups, and fitness groups were only significantly different in their relative risk for prevalent pre-clinical hypertension within the severe obesity group.
Similarly, high fitness was associated with smaller waist circumferences, with differences between high and low fitness being larger in those with severe obesity than with mild obesity.
Based on these findings, the researchers conclude that the favourable associations of having high fitness on health may be similar if not augmented in individuals with severe compared to mild obesity.
However, it is also apparent based on the rather low number of “fit” individuals in the severe obesity category (only about 1 in 10), that maintaining a high level of fitness proves to be more challenging the higher the BMI.