Will My Metabolic Rate Slow Down As I Age?

Picture from Genesispersonalfitness

Looks like we have been very wrong about our metabolic rates. Whether our metabolic rate is fast or slow, it cannot predict weight gain. 

Metabolisms varies by 20 percent or more from person to person regardless of activity level or body composition (Rimbach et al, 2022). So for those of us who run or exercise to manage our weight, yes it does burn calories, but it does not boost our metabolism, at least not in the long term. 

The researchers also found that if you happen to be on the skinnier side, it is not that you have a faster metabolism (Rimbach et al, 2022).

The researchers measured metabolism using doubly labeled water. Participants in their studies drank water containing hydrogen and oxygen isotopes, which researchers can track in the body. How quickly they lost the isotopes through peeing, sweating and even breathing were monitored. These enabled them to ascertain how many calories are burned in that time, or what is known as total energy expenditure i.e. metabolism.

The total energy expenditures studied were measured at 2 time points, ranging from 2 weeks to more than 8 years. Body size and composition were adjusted for since more cells burned more calories and fat and muscle burned calories at different rates. 

The researchers found that the subjects' daily energy expenditures did not change over time. A person with high metabolism today will have it high in a few months or even a few years. Likewise, a person with slow metabolism today will still have it slow in a few months or a few years.

Here's the good news. The researchers found that having a slow metabolism did not make people more likely to gain weight. Nor did having a fast metabolism less likely to gain weight.This is attributed to the human brain's outstanding ability to match calories consumed to calories burned in the long run.

So, running or any exercise is not a magic metabolism booster. Exercise is complex and it affects how our body regulates all its cells, which in turn affects hunger, fullness, immune function and even behaviour. Those who exercise will obviously see day to day fluctations in the calories burned. More on long runs/ hard days compared to recovery days in a later post. Our bodies adjust how much energy we use during our non exercise hours to keep the total caloric burn within a fairly narrow range.

So, you do not gain weight as you age because your metabolism slows down (Pontzer et al, 2021). We have all been mislead by this myth. We should not use it as as excuse. You gained weight because we do not move and/ or exercise as much and because we may have lost some muscle mass.

Reference

Pontzer H, Yamada Y, Sagayama H et al (2021). IAEA DLW Database Consortium. Daily Expenditure Through The Human Life Course. Science. 373(6556): 808-812. DOI: 10.1126/ science.abe5017

Rimbach R, Yamada Y, Sagayama H et al (2022). Total Energy Expenditure Is Repeatable But Not Associated With Short-term Changes In Body Composition. Nat Commun 13,9. DOI: 10.1038/s41467-021-27246-z

Cold Play?

ST 100524

I just wrote about how cold (ice) immersions were not effective last week! And Straits Times does a full page article on the front of their Life Section today (100524).

"I noticed a significant improvement in my alertness and reduced muscle soreness after including cold therapy ....." said a business owner selling ice baths.

No, evidence says cold immersions does not help with recovery. Actually cold immersions inhibits recovery. Researchers (Roberts et al, 2015) have found that cold water immersion after hard exercise suppressed signaling pathways associated with recovery. This suppression lasted for several days.

The newspaper article also credited Wim Hof (the Dutch iceman) for popularising cryo or ice therapy - just like my post. Purveyors of commercial health and wellness have definitely jumped on the same bandwagon. I cannot comment on the various beauty and skincare benefits (such as reduction in cellulite and what not) as touted by the wellness professionals quoted. Please do your due diligence.

Reference

Roberts LA, Raastad T, Markworth et al (2015). Post-exercise Cold Water Immersion Attenuates Acute Anabolic Signaling And Long-term Adaptations In Muscle To Strength Training. J Physiol 593(18) : 4285-4301. DOI: 10.1113/JP270570.

Can Cycling Lower Your Risk Of Knee Arthritis?

Picture by Dennis Thong

I have written previously on what causes osteoarthritis (OA). Definitely not because of overuse nor a mechanical wear and tear process. Especially for those without any previous history of knee truma/ injury, there is very good evidence that OA is actually due to metabolic factors. Well, now a new study (Lo et al, 2024) suggests that cyclists are less likely to develop OA in their knees.

Lo et al (2024) studied 2600 older adults with and without knee OA using knee X-rays, subjective knee pain, and a questionnaire regarding their lifetime history of various physical activities during 4 periods of their lifes: 12 to 18 years old, 19 to 34, 35 to 49 and over 50. 

The study used 3 different outcomes. Persistent knee pain, OA based on X-rays (radiographic OA) and symptomatic OA (having both knee pain and radiographic OA. Note that what is seen on X-ray (OA knees) does not always correspond to pain. This means that some subjects had knee radiographic OA but NO pain.

Almost half the subjects reported some history of cycling and these subjects were less likely to have OA in their knees. How much less? Those with any history of cycling were 17 percent less likely to have knee pain, 9 percent less likely to have radiographic OA and 21 percent less likely to have both. 

Half of those who cycled reported only cycling regularly during one of the 4 age periods, usually the youngest age period from 12 to 18 years old.

Those who cycled during 1,2,3 or 4 of the periods studied reduced their risk of symptomatic OA (i.e. painful knees) by 17, 19, 28 and 43 percent. Meaning lifelong cyclists reduced their risk of symptomatic OA by nearly 50 percent.

The researchers also found that subjects with a history of swimming, strength training and running had lower rates of OA. This is consistent with previous evidence that running DOES NOT ruin your knees despite what every non runner and ex runner you know will insist running does.

You may love watching the beautiful game, but a history of playing the beautiful game (football) even just as a teenager bumped up knee OA risk by a factor of 2. This elevated risk remained even after adjusting for BMI, suggesting that the problem is likely related to acute knee injuries suffered while playing football. 

Picture by Dennis Thong

The researchers concluded that more cycling is associated with less knee pain and favorable to knee health and should be encouraged. 

If you have never cycled previously and would like to start, do note that almost half or the current or former cyclists in the study had radiographic evidence of OA. A quarter of them had symptomatic OA (painful knees). Is cycling better for OA once you do develop OA compared to say running? Is cycling capable of slowing its progression? Currently, we still do not know.

Those of you who have been always been cycling, you definitely have another reason to do so. 

Reference

Lo GH, Richard MJ, Kriska AM et al (2024). Bicyling Over A Lifetime Is Associated With Less Symptomatic Knee Osteoarthritis : Data From The Osteoarthritis Initiative. Med Sci Sp Ex. DOI: 10.1249/ MSS 0.0000000000003449

All pictures by Dennis Thong. Many thanks to Dennis and Eugene Phua for the pictures.