Editor’s note: To actively lose or gain weight has always been decisive – whether for health/fashion reasons or both. Although we do aim to tilt the scale in our favor, there’s basic mathematics hidden behind how much weight can we lose or gain. And interestingly, that depends a lot on our diet, gender, height, weight and age. Club SciWri intern Sanchita Chakrabarty scripts the hidden basics of weight transformation in this article. If you want to be a part of the Club SciWri internship experience, please drop an email at firstname.lastname@example.org.
There has been an increase in incidence of obesity in populations mostly spanning the urban setting of highly developed industrialized countries to developing countries due to a deskbound lifestyle and additional factors. With recent studies connecting obesity to a variety of high risk diseases like diabetes, sleep apnea, cardiovascular diseases, high blood pressure, osteoarthritis and even cancer, it is high time that we became knowledgeable about this topic for our own good. As is in most parts, obesity is related to food habits as well as a sedentary lifestyle. Therefore, understanding the biochemistry and physiological processes of calorie uptake, energy release during bodily functions and different types of exercise ought to be helpful.
The simple math of calorie
A calorie is the unit to measure energy released by food when digested by human body. The body metabolizes the molecules that constitute our diet and converts the resulting calorie into usable energy. Basal Metabolic Rate or BMR is the rate of energy expenditure per unit time, necessary for normal bodily functions including maintaining heart rate, body temperature, respiratory functions, metabolic processes, making new blood cells etc. Resting energy expenditure or REE corresponds to the total amount of caloric requirement in a 24-hour period by the body in a sedentary state. REE and BMR can be calculated using the Harris-Benedict equation, which takes into account gender, age, height, and body weight of the subject and is derived from an indirect calorimetric method. To maintain basic bodily functions and retention of body weight, it is very important to eat healthy food of optimalcaloric value.
Harris-Benedict formula for BMR calculation
|men||BMR = 66 + (6.2 × weight in pounds) + (12.7 × height in inches) – (6.776 × age in years)|
|women||BMR = 655.1 + (4.35 × weight in pounds) + (4.7 × height in inches) – (4.7 × age in years)|
Harris-Benedict formula for daily calorie intake according to activity level
|Sedentary||BMR × 1.2|
|Light exercise||BMR × 1.375|
|Moderately active||BMR × 1.55|
|Highly active||BMR ×1.725|
|Heavy exercise||BMR ×1.9|
Example: If a man is 35 years of age, 6′ tall (72 inches) and weighs 163 pounds (74 kg), then his BMR = 66 + (6.2 × 163) + (12.7 × 72) – (6.776 × 35) = 1753.84 calories/day. Now, if the person lives a sedentary life, he would have to consume BMR × 1.2 = 2104.6 calories in a day to maintain his body weight. To lose or gain weight one has to decrease or increase caloric intake and/or activity level.
As 1 lb of fat corresponds to 3500 calories, there has to be a deficit of 3500 calories to lose weight by 1 lb. Hence, according to the above example, if the man wants to set his weight at 160 lbs (a 3 lb reduction in weight) and starts consuming 1604.6 calories instead of 2104.6 calories (i.e. 500 calories less) in a day, then it would take (3 × 3500)/500 = 21 days or 3 weeks to achieve the targeted weight by maintaining a sedentary lifestyle. Although it is possible to gain or lose weight by altering caloric intake, physical activity is always advisable for good health.
Fat metabolism during exercise
Fat is stored as triglyceride in adipose tissues. Triglyceride consists of three fatty acids attached to a molecule of glycerol. Droplets of triglyceride remain stored in muscle fibers in close proximity of the oxidation sites in muscle mitochondria. During exercise, the enzyme hormone sensitive lipase gets stimulated and dissolves the lipid into three molecules of free fatty acid (FFA) and glycerol, the latter being water soluble diffuses into blood. An increase in plasma concentration of epinephrine that activates betareceptors in adepocytes is thought to be the reason of stimulation of adipose tissue lipolysis. Plasma FFA is the exclusive fat source and fuel during low-intensity exercise. On the other hand, during a high intensity work-out, pools of intramuscular triglyceride are utilized as an additional source of fat. In case of low-intensity cardio exercise, the heart rate of an average person increases up to 60-70% of maximum heart rate within 2-5 minutes. Fat starts to burn if this heart rate is maintained. At this stage, 50% of the total burned calorie comes from fat and if the same intensity level is maintained for 20 minutes, 70-80% calorie comes from fat and the rest from carbohydrate. This is referred to as the “Fat burning zone”. For a high-intensity cardio work-out, mostly referred to as endurance training, heart rate reaches between 70-85% of maximum heart rate and one burns more fat in less time.
Eating at the right time
Studies have confirmed that along with what we eat, when we eat is also important. Superchiasmatic nucleus (SCN), which is a small region within the anterior hypothalamus controls the mammalian circadian rhythm. SCN can synchronize with peripheral tissues and influences the sleep-wake cycle in rhythm with the usual light and dark cycle in a day. SCN also regulates certain behaviors like feeding. Apart from the temporal circadian clock, some peripheral tissues like liver tissues also demonstrate circadian rhythm with the help of cyclically expressed genes. Imbalanced circadian clock has been linked to obesity and type-2 diabetes. Researchers have shown that a change in the circadian timing of feeding results in weight gain in mice. The hormone melatonin plays a major role in regulation of the mammalian circadian clock. Melatonin is very important for proper secretion and action of insulin. Short sleep durations affect melatonin function in turn worsening insulin sensitivity. Recent studies have shown that sleep deprivation is linked to increased brain activity and intake of high calorie food as well as increased desire of binge eating. All of these are directly or indirectly linked to obesity. In general, the rule of having a meal within one hour after waking up and an early dinner still stands true. Also, an early lunch following a good breakfast helps reducing blood sugar level in the afternoon.
Although a cliché, reminding ourselves to eat at the proper time, watch our caloric intake and understand the value of some amount of exercise could be the start of a fight against obesity and its related diseases.
Sanchita completed her PhD from Jadavpur University (Kolkata, India) in Chemistry, followed by a Postdoctoral position at University of Texas at El Paso. Currently she is freelancing in technology scouting and market research and aims to transition into a position where her transferable skills would be put to use. Apart from science she enjoys travelling, writing and reading a lot!
Editor: Sayantan Chakraborty, PhD
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