DR MICHAEL MOSLEY: Exercise will help you keep your brain in shape

DR MICHAEL MOSLEY: Exercise won’t trim your waistline, but it will help you keep your brain in shape

Let me be honest here, I’m not a big fan of exercise. I make myself do daily press-ups and squats, and though I enjoy brisk walks, I never, ever enjoy running.

The main reason I keep at it is because of overwhelming evidence of the multiple benefits that exercise brings. In fact, the latest research suggests it may be even more beneficial for preserving a sharp memory than had been suspected.

But for those who spend lots of time running on treadmills or pedalling away at their exercise bike in the hope of burning off lots of calories, there comes bad news.

Because a new study shows that exercise is even less effective at helping people lose weight than we previously believed to be true.

We have known for some time that exercise alone is not a great way to lose weight. That is mainly because people overestimate how many calories they burn when they are exercising (by as much as three or four-fold, according to at least one study).

Let me be honest here, I’m not a big fan of exercise. I make myself do daily press-ups and squats, and though I enjoy brisk walks, I never, ever enjoy running

And they underestimate how many calories there are in the snack which they reward themselves with after they have been for a run.

In fact, the calories burned by exercise are surprisingly modest.

A few years ago, I had my calorie burn accurately measured while running a mile. This was done using a mask attached to a device that measured how much oxygen I was consuming, and how much carbon dioxide I was breathing out.

The test showed that I burn around 120 calories a mile when running, and about 60 calories a mile when walking.

Which means that if I ate a muffin (roughly 400 calories) then to burn those calories, I would have to run just over three miles or walk six miles, which would take around two hours. But it turns out that those calorie-burning figures are hopelessly optimistic.

The findings of the new study show that, over time, your body compensates for the extra calories you’ve burnt through exercise, by slowing your metabolism down.

Yes, down, not speeding it up. This is exactly the opposite to what we had been led to believe.

They underestimate how many calories there are in the snack which they reward themselves with after they have been for a run. In fact, the calories burned by exercise are surprisingly modest

The assumption has always been that if you exercise more, your metabolism speeds up. While this seems to be true in the short term, it isn’t in the long term. The new study, from the University of Roehampton, looked at data that had been collected by the International Atomic Energy Agency.

Scientists there had carefully tracked the amount of calories that more than 1,750 volunteers burned while going about their normal lives. What the Roehampton team found was that although people use up more calories when they are exercising, their bodies simply compensate by burning fewer calories than normal when doing things such as sleeping.

It turned out that the calories used to keep their bodies ticking over (known as basal energy expenditure) fell by 28 per cent during periods when they were doing regular exercise.

Which, in turn, means the overall impact on our waistlines of doing exercise is less than we might have expected.

There was particularly bad news for people who were hoping to use exercise to slim down, because the effect is even greater in people who are overweight or obese.

This latest study found that if you have a higher BMI (body mass index), then only half the calories you burn while doing exercise translate into real calorie loss at the end of the day.

In other words, if you are overweight, then far from burning 120 calories every time you run a mile, once you include the impact that running has on reducing your metabolic rate, you only really burn through 60 calories.

Depressing, yes, but this is no excuse to hang up your running shoes.

There is plenty of research showing that keeping active will add healthy years to your life, reduce your risk of developing a range of chronic diseases, help you sleep better, improve your mood and even perk up your sex life.

Being active is also good for your brain.

A recent study by scientists from the National Institute on Aging, published in the journal NeuroImage, showed that regular exercise leads to the creation of new brain cells, particularly in the area of the brain associated with memory, which hopefully means you are less likely to develop Alzheimer’s disease and other forms of dementia.

So do keep exercising, but don’t expect that alone to make much difference when you stand on the scales.

As I get older, I look more and more like my dad. He was a lovely man, but not a very healthy one, and I do sometimes worry that I have inherited some of his dodgier genes.

So I was relieved to see a recent study concluded that while the genes we inherit have a powerful impact on our risk of getting a wide range of diseases, from heart disease to type 2 diabetes and cancer, their influence wanes as we get older.

For this study, researchers from Oxford University used genetic data from more than 500,000 Brits and looked to see what impact their genes had on the chances of becoming ill.

They found that the impact of many of the genes, particularly those linked to conditions such as high blood pressure, skin cancer and underactive thyroid, faded with time.

Why exactly this happens, and why it affects some diseases more than others, is still a mystery.

But I am hoping this means that my current healthy lifestyle will come out on top.

My attention was grabbed recently by a headline which claimed that: ‘Eating a hotdog could take 36 minutes off your life.’

This came from a study by the University of Michigan, U.S., where they worked out the impact on our health of eating a serving of more than 5,800 foods.

One of the examples they cited was hotdogs, which they said took 36 minutes off life expectancy. But on the plus side, eating a small handful of nuts could add 26 minutes.

But how do they come up with these figures? I dug more deeply into other research, which broadly agreed that eating a serving of processed meat daily is associated with a 15 per cent higher risk of ‘all-cause mortality’. In other words, your risk of dying over the next year is 15 per cent higher if you regularly eat processed meat than if you don’t.

If you do some clever calculations, that translates into about 36 minutes shaved off your life for every hotdog you eat.

Which you may, or may not, decide is good reason to leave hotdogs alone.

I am suspicious about the precision of these numbers, but I like the approach to try to make the relative risk of eating different foods a bit clearer.

Sir David Spiegelhalter, a statistician at Cambridge University, has taken the idea further with something he calls ‘microlives’. This involves estimating how much any given activity will add, or take away, from your life.

Based on studies he calculated that smoking two cigarettes, having two alcoholic drinks, eating a portion of processed meat, being 5 kg overweight or watching two hours of TV a day will all knock about 30 minutes off your life.

But taking a statin could add 30 minutes, while doing 20 minutes of moderate exercise daily will add an hour. Even better, getting your five-a-day could add two hours.

What I deduce from this is that if you eat a good diet and stay active, it is unlikely that consuming the odd hotdog is going to make a lot of difference to your life expectancy.

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