What is Metabolism and How Does It Change with Age?
By Gary M. Pepper, M.D. and Sam Jeans, MSc
Our bodies undergo many transitions as we age, some good and some not so good!
In the latter category of “not so good”, many people tend to struggle more with their weight as they get older. Obesity rates are higher in older populations, and in the United States, more than 30% of both men and women over 60 are obese.
Obesity in older age brings about much of the same risks as it does at any age, including an increased risk of heart disease, diabetes, high blood pressure, stroke, and mobility problems, and the risks climb ever higher with each year that goes by!
Unraveling what happens to our metabolism as we age helps provide strategies for staying healthy and reducing the risks of putting on excess weight. The popular consensus is that, as we age, our bodies ‘slow down’, which makes it tougher to keep weight off, but does that really tell the whole story?
Metabolism Defined
At its most fundamental, metabolism encompasses every chemical process required to sustain life. It’s easy to confuse the entire concept of metabolism with just the basal metabolic rate (BMR) alone, but this is just one component of metabolism.
Many people use the terms interchangeably, whereas, in fact, there are three main components to metabolism:
1: The Basal Metabolic Rate (BMR)
The body is in constant motion, so even when we’re totally sedentary, sleeping, or otherwise at rest, we require energy and nutrients to function correctly.
So long as the heart pumps, the lungs breathe and the body and its organs go about their business growing and repairing cells, we are utilizing energy in one form or another, and this is our basal metabolic rate (BMR).
The BMR varies depending on the following factors:
Body Size and Muscle: Larger bodies have greater energy demands and higher BMRs.
Lean Muscle Tissue: Whilst it’s true that larger bodies have greater energy demands, BMR also increases relative to the proportion of the body that is made up of lean muscle. Muscle burns more energy than most other tissues.
Body Fat Percentage: Fat burns energy at a much lesser rate than most cells. A high body fat percentage relative to lean muscle tissue results in a lower BMR, even if the body itself is physically larger.
Age: Age does affect the BMR for a few different reasons, which we will discuss shortly.
Growth: Younger children have generally higher BMRs due to body growth, and they also need more energy to maintain their body temperatures.
Gender: Men likely have higher BMRs than women on average as they’re larger and have higher percentages of lean muscle tissue.
Genetics: Genetics do play a role in BMR, but there is debate surrounding quite how drastic the influence of genetics is compared to other factors.
Hormones: Hormone levels, particularly those governed by the thyroid gland, also influence BMR. Hypothyroidism (sluggish thyroid function) is associated with a lower BMR whereas hyperthyroidism (excessive thyroid function) is associated with elevated BMR. Metabolism-related hormones are also influenced by diet, for example, iodine deficiency may result in an underactive thyroid that lowers BMR.
Activity Level: Whilst physical activity burns energy directly as a result of exercise, it also raises BMR by stimulating the growth and repair of new cells, such as muscle cells.
Infection: Infections stimulate an immune response that requires energy, thus boosting BMR.
Environment/Temperature: Colder environments may increase BMR slightly as our bodies work harder to maintain a stable core temperature. Conversely, hotter environments may increase BMR as our bodies work harder to cool down.
2: Thermic Effect of Food (TEF)
The consumption of food itself requires energy and some foods are much easier to digest than others.
It takes considerable effort for our bodies to move food through the digestive system, and our body also needs to absorb and transport nutrients from that food, which further requires energy.
A concept that tends to pop up in various diet plans is ‘calorie negative food’ – that is food that burns more calories to digest than they provide as food. Sadly, there is no evidence that we can ‘eat ourselves thin’ by consuming calorie-negative food!
TEF varies considerably depending on the food consumed and its macronutrients content:
Fat has a thermic effect of some 0 to 5%, which means that for every 100 calories of fat consumed, the body burns just 0 to 5 calories
Carbohydrates have a thermic effect of around 5 to 10%, so for every 100 calories of carbs consumed, the body burns just 5 to 10 calories.
Protein has a much higher thermic effect of around 20 to 30%, so for every 100 calories of protein consumed, the body burns 30 calories (Source: Healthline).
Thirdly, our body requires energy to sustain movement and exercise. This is highly variable and obviously depends on physical activity levels – the more we move, the more energy we require to breathe, fuel our muscles, and repair cells.
Common estimates suggest that physical exercise uses between 15% and 30% of average daily energy expenditure. Engaging in intense or protracted physical exercise ( such as running a marathon) will increase that figure.
The total accumulative energy required for these 3 metabolic components – BMR, TEF, and TEE, makes up our total daily energy expenditure.
In Part 2 of this article, we will cover how aging affects our metabolism and what we can do about it. Check back at metabolism.com for the publication date.
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The mission of the The Thyroid Project is to encourage sharing of information and experience between the public and the medical community about the treatment of hypothyroidism (low thyroid function). For at least the past few decades there is a growing awareness of “something missing†in the way suffers of hypothyroidism are treated for their disease.
Too many patients, as documented in an on-line study of 12,000 individuals conducted by the American Thyroid Association published in June 2018, (https://doi.org/10.1089/thy.2017.0681) , complain of persistent symptoms of hypothyroidism despite what their doctors believe is successful treatment with levothyroxine (brands include Synthroid, Unithroid, Tirosent, Levoxl). We believe something needs to be done to resolve this conflict between patients and their doctors.
By Gary M. Pepper, M.D. Ozempic, Rybelsus, Trulicity, Wegovy, Saxenda are the central players in the weight loss craze sweeping across the globe. Metabolisim.com has been monitoring this phenomenon from its beginnings in 2008 with its report “Lizard Spit Reduces Blood Sugar and Appetite”, regarding the first drug in this class, Byetta (exenatide). Caught In the middle of the current chaos are the medical experts who treat diabetes and have been prescribing these medications for more than a decade. Here is a brief commentary from one such board certified endocrinologist; “I started treating Type 2 diabetics with GLP-1 agonists more than 10 years ago. In some respects, these medications have revolutionized the treatment of diabetes by lowering blood sugar effectively and promoting weight loss at the same time, a unique combination of benefits. Not everyone benefits from these drugs to the same degree unfortunately, and I have seen lots of patients experience unacceptable side effects from them. Nothing though, has prepared me for what is happening now. Too often, I find myself confronting someone who expects me to prescribe one of these drugs just so they can lose weight. Sadly, one extreme example was someone who, despite battling a life threatening medical condition, was insistent on getting a prescription. At the same time my diabetic patients are scrambling to find a place to buy their medications if they can even afford it. It is disheartening, to say the least, and I dread the negative interactions with some of my patients I now face almost daily.”
Off- Label Use
The FDA is the U.S. government’s department tasked with evaluating and approving drugs for specific medical conditions. When a new medication is approved for treating a medical condition by the FDA the agency will, at the same time, set strict guidelines for exactly which patients may use the newly approved drug. When a medication is used “off-label” it means that these limitations are being overridden by the provider for a potential benefit which outweighs the drugs risks. It is a general misconception that off-label means illegal; it does not. This practice has been going on for ages and more than 20% of prescriptions in the United States are prescribed off-label. A common example is the use of beta-blockers (approved for heart problems) for the treatment of performance anxiety.
GLP-1 agonist drugs, as discussed recently by metabolism.com. were originally approved for the treatment of Type 2 diabetes in adults. In the past few years most of these same medications have gained unprecedented popularity for their “off-label” weight loss benefit. Of the 5 GLP-1 agents presently in U.S. pharmacies only Wegovy (semaglutide) and Saxenda (liraglutide) are FDA approved for treating obesity. Of these two, Wegovy is the newer and had been much more popular that its sister drug Saxenda, probably due to being dosed only once weekly compared to daily for Saxenda and less likely to cause side effects. Due to Wegovy’s soaring popularity, its manufacturer, Novo Nordisk, increased the price of Wegovy two times since its initial release.
by Gary M. Pepper, M.D. and Sam Jeans, MSc The global anti-obesity drug market, in 2021was valued at over $2 billion. Within one year this figure had skyrocketed to $8 billion and is expected to climb to nearly $ 20 billion by 2027. This astounding growth is a reflection of soaring obesity rates, and the arrival of a new class of weight loss medication fueling a craze both in the USA and across the world.
The FDA and global health regulators, until very recently, had maintained a very tight ship when it comes to treating obesity with medication, placing the emphasis on diet and exercise rather than weight loss drugs. Since the 80s, anti-obesity drugs continued to be controversial, and a more stringent FDA implemented ongoing safety trials along with other precautions. There is some speculation that a shift in attitude toward approval of weight loss medication by the FDA , is underway
Weight loss drug controversies are far from over and, in fact, may soon rival the amphetamine crisis of the 70’s. For that reason, metabolism.com has felt it important to provide our guide to weight loss drug issues, past and present.
Anti-Obesity Drugs Timeline
Prescription drugs for lifestyle diseases such as obesity were marketed heavily throughout the 1950s to the 1970s. Amphetamines entered the public domain after the Second World War where they were used extensively in the military.
In the 50s, walk-in clinics prescribed diet pills with other medications almost at random, with or without genuine concern for one’s weight. These brightly colored pills became known as “rainbow pills”.
In the 1960s and 1970s, the so-called “rainbow pill diet” of pills was finally coming to an end as the FDA began to systematically ban many of the drugs involved. A high-profile expose by investigative journalist Susanna Mcbee, published in Life magazine, brought attention to this new modern public health crisis.
The rainbow pill diet combined amphetamines, laxatives, thyroid hormones, and even diuretics to produce extreme weight loss, combined with benzodiazepines, barbiturates, and steroids to reduce side effects, and antidepressants to suppress medication-induced insomnia and anxiety.
In 1968, rainbow pills were linked to over 60 deaths, with numerous accounts of their devastating impact surfacing in the news and media. Within just two months, 48 million pills were seized and destroyed. Nevertheless, amphetamine-based diet pills remained extremely popular throughout the 1970s. In 1978, some 3.3 million prescriptions for amphetamines were written each year, with some 50 million pills a year ending up in the black market.
In 1979, the FDA banned amphetamines as a weight loss aid, but that is hardly the end of the USA’s love affair with obesity medication.
Here’s a brief timeline of recent anti-obesity drugs:
Lack of energy and inability to lose weight are constant challenges for many people and are every day complaints encountered in the doctor’s office. Almost anyone can find some relief from these problems by accessing the healing properties of physical activity. Mentioning to a patient the need for ‘more exercise’ often causes rolling of the eyes, sighing, shrugging, snorting or worse yet, the hundred-yard stare. We all know exercise is important but who has the energy for that? It seems like a vicious cycle. Surprisingly, when done correctly, exercise can improve energy with the additional advantage of promoting weight loss and restoring tone and stamina. It is helpful to remember that the human body was designed for a lot more physical activity and a lot less food than we are privileged to experience in present day life. It therefore takes will power and knowledge to maintain the environment required for optimal health. Here are eight steps to get in the swing of regular exercise. Some suggestions may surprise you.
