What is "middle age spread"? It's when people start piling on the pounds in middle age and the measurement around their waist/hips starts to increase each year.

The definition of "middle age" is vague, but it's roughly between the ages of 40 to 60, when you're no longer young, but also not elderly.

Why does middle age spread happen?

Well, some people think it's due to a gradual slowing of our metabolic rate. Other think it's due to people becoming more sedentary as they switch from playing sports and generally moving around often to doing less exercise, watching more TV and having sedentary jobs. Another factor is that being stressed from the responsibilities of middle age such as raising kids, looking after a home and being productive at work contributes to eating a poor diet or simply consuming too much food.

What does the new study say?

One of the points, above, has been disproved by a new scientific study from Duke University in the USA where they pooled data from 6,421 children and adults aged 8 days to 95 years from 29 countries. The participants had been given isotopically labelled food and drink which could be traced by scientists, allowing them to measure the metabolic rate of each person.

It turns out that our metabolic peak is at age one, when we burn 50% more calories than an adult, after adjusting for weight. From that early peak there's a decline until age 20 when it hits a stable level until age 60 when it declines again. Adults in their 90's use 23% less energy than middle-age adults do.

So, "middle age spread" is not due to a decline in our metabolic rate in middle age. While that would be a great excuse, it doesn't seem to be true. In which case, the spread comes from eating too much and moving too little.

Lose weight sensibly

However, if you choose to lose weight, please do so sensibly over time. Do not go on a crash diet or you could well prime your body to fight back via epigenetic changes and make weight loss more difficult which could result in you re-gaining any lost weight, thereby impacting your mental health and creating a vicious circle.

Speculation: One of the reasons for middle-age spread could possibly be that, by middle age, a lot of people will have dieted in an attempt to lose weight, but did it rapidly and initiated epigenetic changes in their bodies which decreased their resting metabolic rate. When they went back to eating the same diet as before they'd gain back more weight due to their lower metabolic rate, for as long as the epigenetic changes lasted.

Headlines on websites like this don't help... "How to shed middle-age spread: Banish the dangerous spare tyre in just six weeks".

Firstly, you can't just target your "spare tyre" or "middle age spread", you'd have to lose weight all over... from your hips, back, thighs, face, everywhere. You can't "spot reduce" fat.

Secondly, how much weight would someone have to lose to "banish" their "spare tyre"? Presumably they'd have to lose almost every pound of fat on their entire bodies. Is that feasible in six weeks? No, but it highlights the propensity of humans to want quick fixes. Unfortunately, those quick fixes (crash diets) are likely to cause more harm than good.

Thirdly, a lot of the processed food we eat initiates epigenetic brain changes similar to those seen in addiction. Trying to switch from that to a specialist weight-loss diet is like going cold turkey and will be too hard for many people. A better idea would be to reduce the amount of junk food in your diet slowly over time and let the brain adjust to new, wholesome food.

Why do teenagers eat so much?

Some people have asked about our teenage years, when we seem to eat an enormous amount of calories, but not gain weight. Why isn't that reflected in this study? Apparently, the basal metabolic rate (BMR) doesn't change. While that's counter-intuitive, it seem that the rate at which the body burns fuel is still comparable to adults, but hormonal changes induce growth and that requires more energy. It's not that we just magically burn more calories, we use them to grow.

Interestingly, another study showed that children, not newborn babies, have the highest brain utilisation of energy, when the brain uses 43% of the entire caloric input each day!

Imagine what's happening in the brain at that time. The child's genetics have been set in stone since the embryo was formed, but during childhood the brain consumes 43% of all energy the child takes in. Why? It must be due to growth and re-modelling of the brain in response to external stimuli as well as perhaps an in-built developmental path. It's not surprising that any external stimuli at that age can have life-long impacts including adverse mental health ones.

The good news is that your brain, with its 100 billion neurons and 1 quadrillion connections, can re-model itself in real-time.