As a physical activity advocate, friends and acquaintances often get “defensive” by impressing on me how they have started or are planning to start regular exercise to lose weight. As the new year is fast approaching, it would not be too long before it gets busy in the gyms, sadly, for a short-lived goal of losing weight through exercise. It is worth emphasising that our ancestors had a lot of reasons to move and engage in high levels of physical activity, but weight loss was not one of them. To be fair, it is self-evident that physical exercise elicits the instant burning of calories that is accompanied by spontaneous huffing and puffing, including the obvious breaking of sweat and the feeling of after-exercise fatigue. For decades, this practical experience led the public health community to wrongly assume that the number of calories one burns in any given day depends, in part, on how active one has been that day. In other words, the so-called total energy expenditure was deemed flexible and additive, thus implying that the more active you are, the more calories you burn and invariably the more weight you lose.
This assumption flies in the face of the fact that modern medicine is based on primarily maintaining and restoring homeostasis, a term that explains the auto-regulating processes that keep the internal body environment humming within narrow physiological limits. In this context, it would surprise no one that the body temperature and blood sugar of all humans run within the same narrow range, whether one is white, black, red or yellow and these values remain the same if one lives in the hot desert climate of Timbuktu, Mali or resides in the subarctic climate of Anchorage, Alaska. Baring a condition of illness, and to paraphrase Dr. Martin Luther King in physiological term: the long arc of homeostasis is long and bends toward the same normal range for humans of all races in different geographical locations. For instance, my blood may be fluxed with high levels of glucose that may be dangerous to my health following a delicious carbohydrate meal, but my body would vigorously work behind the scene to reduce the blood levels to an acceptable range within three to four hours. That is homeostasis!
In same way that the blood sugar level of humans’ stays the same, and contrary to flexibly additive total energy expenditure, a 2012 study found that all adults across all populations burn about the same amount of energy per day, irrespective of lifestyle and culture. This goes to say that a skinny peasant farmer in my village, in Nigeria, expends the same calories on daily basis as an overweight friend in America. In what the authors termed “constrained energy expenditure”, this study found that the Hadza people, a small society of hunter and gatherers in Northern Tanzania, burn the same number of calories per day as any random obese or overweight person living in the US or Europe, in spite of their high physical activity levels.
As the first generation of humans who diet and engage in leisure physical activity, commonsense assumes that exercise would be a great tool for reducing weight. However, we fail to realise that weight problem is uniquely ours, as no previous generations had the privilege of food abundance, and therefore none had the high incidence of overweight and obesity issues. For instance, no one goes to the gym because they are hungry or, in some earnest anticipation, to obtain food but does so with the hope of expending some calories. In stark contrast to our experience, our ancestors did not have huge food supplies and had to engage in physical movement only when hungry or when they perceived the threat of running of out of food. In other words, hunger or food insecurity stimulated voluntary foraging behaviour, which basically meant expending energy to obtain energy. If physical exercise additively leads to the unregulated burning of calories and weight loss, without a buffer, as we naively hope, our ancestors who were physically active under chronic food insecurity would have been starved to dead before any hope of obtaining food and by extension none of us would be here!
It turns out that the energy to keep the internal body environment at a consistent narrow state (homeostasis) is highly regulated and not unlimited. It is therefore physiologically impossible to allocate unlimited calories to physical exercise in order to keep losing weight without a plateau. Literature shows that an average 50-year old has about a 2,500 “calorie budget” per day that must be allocated to various physiological tasks. What this means is that you may jam in 4,000 calories of energy per day in term of consumption, but the body is “constrained” to expend only 2,500 calories. Since the energy to support homeostasis and keep internal body environment constant is not unlimited, the body allocates and prioritises this limited energy to different physiological tasks.
The constrained energy expenditure theory is attributed to why extreme sporting activities reduce energy allocation to the immune system, leading to immunosuppression that puts elite athletes at risk of infections. Intense exercise also reduces sex hormones and explains why female athletes may stop having menstrual cycles, a condition called athletic amenorrhea. All said, regular exercise would primarily provide an anti-inflammatory environment and keep the “mad dog” immune cells calmly under the hood to prevent inflammatory diseases such as diabetes, heart diseases, certain cancers, Alzheimer’s and other chronic diseases. While you may lose some weight with physical exercise, you are better off cutting back on consumption through occasional fasting and calories restriction. Three meals a day is relatively a new phenomenon in the context of human history and regular physical activity is as old as man.
Mukaila Kareem, a doctor of physiotherapy and physical activity advocate, writes from the USA and can be reached through makkareem5@gmail.com
Credit: Mukaila Kareem, PT