Physiqonomics Weekly #59: It’s Still Not Your Metabolism

19 August 2021 | by Aadam

Hey,

It’s time for another instalment of Physiqonomics Weekly.


AADAM ANSWERS

Q-I have had a major surgery but plan to get back to exercise as soon as possible. Should I adjust how I eat during recovery, when my only exercise will be walking and PT? Should I change nutrient mix to promote healing?

If you’re recovering from surgery (or injury) then increase calories to maintenance and ensure you’re consuming about 1g/lb of protein. Some studies suggest increasing protein to ~1.2g/lb could be beneficial (Tipton KD., 2015).

Then, if you’re losing weight, bump up calories by 10% until weight loss levels off. Conversely, if you’re gaining weight, reduce calories by 10%.


THURSDAY TIDBIT

It’s Still Not Your Metabolism

We all know our metabolism slows down as we age, right? And it’s because of this metabolic slowing we tend to gain weight the older we get. Right. Right?

Wrong.

A brand new study led by professor John Speakman used doubly-labelled water data from 6421 people (aged 8 days to 95 years) from 29 different countries and, after accounting for fat-free mass and fat mass, found that, actually, no, it doesn’t.

In fact, between the ages of 20 to 60 years, total energy expenditure and basal metabolic rate remain stable.

Then, from about 60 onwards, total energy expenditure and metabolic rate slowly begin to decline (-0.7% per year), along with fat-free mass and fat mass.

However, this decline in energy expenditure isn’t just related to a loss of fat-free mass. As I explained in my slow metabolism article, this is also due to reductions in anabolic hormones such as testosterone, estrogen, and growth hormone and a decline in mitochondria activity.

For subjects over 90 years, adjusted energy expenditure was ~26% less than that of middle-aged adults.

Adjusted total energy expenditure remains stable from ages 20-60, then slowly begins to decline
Adjusted basal energy expenditure remains stable from ages 20-60, then slowly begins to decline

They also found there were no sex differences (once adjusted for fat-free mass and fat mass) and neither was there a change around menopause. This effect held true even for pregnant women. As the researchers write:

Adjusted total and basal expenditures were stable even during pregnancy; the elevation in unadjusted expenditures matched those expected from the gain in mothers’ fat-free mass and fat mass.

So what gives? Why do people gain weight as they age?

1- We lose muscle as we age

Muscle mass is tightly linked to metabolic rate. The more muscle you lose, the more your metabolic rate will drop. While a lot of this reduction is an inevitable consequence of ageing, you can mitigate this to some degree by resistance training (and eating adequate protein).

Resistance training also has an effect on another component of energy expenditure: NEAT (non-exercise activity thermogenesis). Some studies have shown that unlike cardio which leads to a reduction in NEAT, strength training leads to an increase in NEAT.

As the authors of a 2018 review explain: (Doucet et al. 2018)

Aerobic trials cause a decrease in NEAT likely due to an increase in fatigue associated with aerobic training. However, resistance training leads to increases in NEAT and total daily energy expenditure as muscle mass and strength improve.

Said another way, the better you can preserve muscle and strength as you age, the more physically active you’ll stay which can increase energy expenditure.

2As we get older, our physical activity levels drop but energy intake remains the same

This shouldn’t be surprising. As we get older, life takes over and we move around less. We go from walking to driving. Instead of partying our faces off all night, we curl up on the couch and watch Netflix. The sports we used to play at school are replaced by watching sports on TV.

Unfortunately, while our physical activity declines, our food intake doesn’t; creating an energy imbalance (we’re eating the same amount, if not more, but move around less resulting in an energy surplus).

Westerterp KR. (2009) observed young adults over a period of 10 years and found going from a physically active to a more sedentary lifestyle didn’t lead to an equivalent reduction in energy intake.

Interestingly, those who had the highest physical activity at baseline also experienced the highest fat gain later on. Why? Well, the high levels of physical activity in their younger years protected them against weight gain. But as they aged, and their activity levels dropped, their eating habits didn’t change. Result: energy surplus.

Now, before I get angry messages from people telling me how the results of this study don’t apply to them because *insert whatever reason here*, I want to be clear that yes, fat loss can be harder for some people. And there can be a host of health issues that can make it even harder.

And I’m not downplaying that.

But my response is always the same: Ok, and? If you want to make progress, focusing on the things you can control is going to be infinitely more productive than adopting a fatalistic attitude where you blame your lack of progress on everything else but your current behaviours.

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#TBT

– The Truth About Your Slow Metabolism


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–Aa


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