By Gary Pepper, M.D., and Sam Jeans MSc
It’s tempting to think that our bodies simply ‘slow down’ as we age, which makes it harder to keep weight off, but a study of 6,600 people aged between one week old to 95-years-old revealed that it’s not as simple as one might assume.
In our prior post, we defined what metabolism really is (a mixture of at least 3 different processes), so we can now move on to discussing how these processes change as we age.
A 2021 study, published in Science, found that our total daily energy expenditure is 50% faster in our first year of life than during adulthood. After our first birthday, our daily energy expenditure begins to taper off by some 3% each year until around the age of 20.
But here’s the surprise; instead of our total daily expenditure slowing gradually from say, the age of 30 onwards, it tends to remain very stable until the age of 50 or 60. After then, it decreases only slightly, by around 0.7% per year.
“Some people think of their teens and 20s as the age when their calorie-burning potential hits its peak…But the study shows that, pound for pound, infants have the highest metabolic rates of all.” – Dr. Katzmarzyk, Professor and Associate Executive Director for Population and Public Health Sciences at the Pennington Biomedical Research Center.
In essence, what this study shows is that the metabolism – and total energy expenditure – slows over time because of a mixture of factors, and not just because of age only. In other words, many people gain weight as they age for reasons other than what is often simply described as “the body slows down as you age”.
If you’re struggling more with your weight as you age, there are probably a few different things going on.
Diets can change in either direction with age, they might vastly improve as we realize the benefits of a healthy diet, or they might slip deeper and deeper into bad habits and indulgence!
What we do know is that a high-fat, low-protein diet lowers the thermic effect of food, which means that more excess calories end up deposited as fat.
A 2016 study from Purdue University found that a high-protein diet can boost the metabolism, boosting energy expenditure by around 100 calories per day. That’s 100 calories you’re losing for free, without moving, simply by eating high protein foods. For how long the increase in calorie burning by high protein diet lasts, is not clear, however.
Grabbing a shelf full of protein supplements in your 50s, 60s, or 70s is probably not required.
The following is a list of natural high-protein foodstuffs to consider:
- Beans, peas, and legumes
- Unprocessed dairy
- Oats and grains
- Dark leafy vegetables
Next up, it’s all too easy to start moving less with age. Rather than low-level exercise, it’s usually the more vigorous activities that start getting neglected with age.
Exercise demands remain quite consistent throughout life, and it’s generally now recommended that older adults up to the age of around 50 to 60 commit to a similar exercise regime as those aged much younger. The older we become however, limitations on exercise duration and intensity are imposed by illness and degenerative conditions such as arthritis, heart and lung disease and whatever injuries have occurred over the years.
A strong body of research has also found that more rigorous exercise like high-intensity interval training can protect seniors from an array of diseases whilst bolstering their metabolism. It is strongly advised, particularly in older individuals, that before stepping up your exercise regime to always consult a physician prior to starting.
Muscle loss (sarcopenia) reduces BMR whilst simultaneously reducing the number of calories burnt during exercise. Harvard Health cites that muscle loss can hit 3% to 5% per year after the age of 30. A higher percentage of lean muscle tissue boosts the level of calories burnt during exercise and at rest, so fighting against muscle loss is a potent way to maintain a steady metabolism.
It’s possible to fight against muscle loss by engaging in strength and resistance training in addition to your standard exercise regime. Follow a strength or resistance training plan approved by a professional, aimed at your age group and skill level and always take things slowly at the start.
The hormone levels of both men and women progressively change with age.
Whilst men obviously do not experience anything like the level of hormone change that comes with female menopause, they may still experience somewhat of a “male menopause” which involves the loss of testosterone often beginning during the 50’s. Obesity in men is also associated with lower testosterone levels, creating a vicious cycle of increasing obesity causing lower testosterone which then inhibits the ability to lose weight, and so on.
Medical News Today primarily recommends lifestyle changes to support hormone levels, including increasing exercise and decreasing consumption of processed and fatty foods. Limiting alcohol consumption is also recommended not only to reduce caloric intake but alcohol may also suppress male hormone (testosterone) production.
Some herbs and supplements are also suggested to support metabolic hormones – Ginseng, Maca, and Ashwagandha are amongst those that show the most promising preliminary evidence, though large-scale studies are still lacking.
Age does affect the metabolism, but it’s not as simple as your body just “slowing down” as you get older – and we are not powerless to stop it!
We have greater control over our metabolism than generally assumed and making just a handful of small changes might be all it takes to beat the “middle-aged spread”.
Considering all 3 components of the metabolism – BMR, TEF, and TEE – helps target strategies aimed at improving each, such as switching to a high-protein diet to increase calorie burning during eating, increasing exercise, and also supporting hormone function, and increasing lean muscle mass to boost BMR.
A combined, holistic approach provides a much better outcome than focusing on just one part of the metabolism in isolation of the others.