My entry for the 2020 Images of Research competition was designed to transmit an impactful message on the importance of how obesity is classified (BMI vs. body fat) and why that matters. This message is even more pertinent in today’s society, with record levels of obesity alongside the COVID-19 pandemic, which is independently associated with an increased risk of mortality in patients who are obese, as defined by their BMI. It is imperative to note that this increased risk is not owing to high overall mass relative to an individual’s height, but through high levels of body fat increasing BMI. Herein lies the inherent problem with BMI, because the calculation (mass [kg] ÷ height[m]2) does not differentiate the mass between each individual component of body composition (i.e. muscle, fat and bone).
The two main components of total body mass are body fat and skeletal muscle, with interestingly bone mass only contributing to an average of 1.37 – 4.42kg (~2-4%) of an adult’s total mass, eliminating the theory of ‘heavy bones’ in some cases being used as an excuse for the cause of obesity. It is important to note that whilst high body fat and low muscle mass have deleterious consequences for physical function and disease risk, they both have important roles in the maintenance of homeostasis. For example, a normal body fat range serves as an energy store, protects from impacts, preserves heat loss, and is involved in hormone regulation and metabolism. Whereas skeletal muscle, on other hand, is involved in mobility, stability, postural control, and is a potent regulator of immune system function.
However, when body fat and, in particular, visceral fat (fat stored around your waist and organs) exceeds this normal range, body fat acts as an endocrine organ, creating an environment of low-grade systemic inflammation. This environment is conducive to negatively affected immune function, promoting disease (i.e. diabetes) and accelerating muscle loss, which in turn can create a vicious circle in muscle loss and fat gain, leading to disability, illness and a reduced quality of life. This specific example is reflected in my 2020 Images of Research entry, depicting one method of classification portraying a normal weight individual (BMI equal or less than 25) and one method classifying an obese individual (body fat greater than 40%), yet these are both the same individual. This particular situation is especially observed in older adults who are at greater risk of COVID-19 mortality independent of obesity, but when combined, the risk increases further. The mechanism can be traced back to the low-grade systemic inflammation environment created by high levels of adiposity and demonstrates why reducing body fat over just BMI is a key message that needs to be disseminated to both younger and older adults.
My research in particular has examined multiple classification methods of obesity to document any deleterious consequences on skeletal muscle, tendon and bone properties. The results revealed that being obese as defined by body fat percentage (40% and over in women and 28% and over in men) over BMI was associated with lower muscle activation capacity, reduced relative strength, poorer muscle quality, an acceleration in muscle atrophy (loss) as you age and finally an increased risk of developing osteoporosis. All of these findings would contribute to a decrease in physical function performance and an increased risk of injury. Nevertheless, to avert these negative consequences, increasing both calorie intake alongside increased physical activity was found to be beneficial to both skeletal muscle and bone health in older adults. The implications of these findings support the prioritisation of reducing body fat over BMI, due the need to maintain if not build skeletal muscle as we age to avert potential functional difficulties, which interestingly could result in an increase in BMI but a reduction in body fat percentage.
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David was a finalist in the 2020 Images of Research competition. The 2021 competition will launch soon. Check out the celebratory brochure and website here: https://www.mmu.ac.uk/research/research-study/events/images/