[chris (OP)]

Recently I was in Perth for the Science on the Swan conference where I also delivered a public lecture on healthy living, which included a Q&A session. There were some follow-up questions, which I am answering here; this is one of them:

Hi SotS!

Firstly, thank you for organising the free public talk with Dr Chris Smith, I enjoyed it immensely. It was a refreshing way to discuss health issues and the best part was the Q&A session at the end. Anyway, some questions I would have asked:

1.       Sugar - surely it can't be as bad as it's made out to be by that "I quit Sugar" lady. Right?
2.       I have a sit-stand desk at work. Is it all it's cut out to be or is it just a fad?  (I don't feel any fitter, but as I am desk-bound most of the day, I find that I do enjoy standing part of the time)
3.       What's all the technology like mobile phones doing to people's eyes? And thumbs? What are the dangers if we are constantly online during all our waking hours?

[chris (OP)]

1. Sugar - surely it can't be as bad as it's made out to be by that "I quit Sugar" lady. Right?

The guidelines for what constitutes a healthy diet suggest that, of your daily energy intake, 50% comes from carbohydrates, 30% from fats and 20% from protein.

Confusingly, alongside starch and fibre, simple refined sugars, like sucrose, glucose and fructose, are also carbohydrates; but that doesn't mean you should acquire half your day's calories in the form of sugar. A small amount of sugar is not at all harmful, but these "added sugars" probably shouldn't constitute more than 10% of your day's calorie intake.

The rationale for limiting refined sugar intake is that these simple sugars are absorbed very rapidly from the small intestine. Upon entering the bloodstream they trigger an immediate surge in blood glucose, which in turn provokes a spike in insulin secretion from the pancreas. This sends blood sugar levels plummeting again, making you feel hungry, so you are more likely to want to eat again, and promotes the conversion of the sugar into fat.

Fat is much harder to metabolise in our tissues compared with carbohydrates, so the body preferentially uses the latter, meaning that fat tends to accumulate over time, including around our internal organs, and this is linked to a higher rate of diabetes, fatty liver and metabolic syndrome.

For these reasons, complex carbohydrates are preferred over refined sugars. This means eating things that contain starches and fibre, which take longer to digest and hence "trickle" sugars into the circulation, can contribute to long-term maintenance of blood glucose rather than a "sugar tsunami" that you get from a chocolate bar.

2.       I have a sit-stand desk at work. Is it all it's cut out to be or is it just a fad?  (I don't feel any fitter, but as I am desk-bound most of the day, I find that I do enjoy standing part of the time)

Is sitting the new smoking? Some say so. It's certainly true that the majority of the working population now do a sedentary job. This is in stark contrast with 50 years ago when nearly half of workers were engaged in some sort of physically-active workplace role and only about 5% of people sat down all day. Obesity levels have ballooned, like waistlines, in the last 2 decades; now more than a third of the world population is obese, half are overweight and, in the UK (but also in Australia and the US) at least one in four children starting primary school is overweight.

People have not changed genetically in the last 2 decades to account for this dramatic shift in population body mass index. Instead this must reflect lifestyle and dietary choices as well as a shift in social norms that mean that people regard being overweight as more acceptable than they did in the days of Enid Blyton (where no children's story was complete without a kid called "Fatty"). This means that people are less motivated to do something about the problem.

The sad fact is that, despite better healthcare and a greater corpus of knowledge about health and disease than we have ever had, the present generation are likely to live less long that their parents. Many are destined to die of "diseases of civilisation" brought about by the modern lifestyle and we need to address this urgently.

The essential missing ingredient is exercise. There is no drug that a doctor can prescribe that is even half as good at cutting disease risk like modest physical activity. In fact, if exercise were discovered tomorrow people would hail it as a wonder pill and prescribe it to everyone.

Just standing up all day at work won't solve everything, but it does make people mindful of the need to move about; it does boost metabolic rate and it does encourage people to be more active, all of which raise basal metabolic rate and burn calories.

3.       What's all the technology like mobile phones doing to people's eyes? And thumbs? What are the dangers if we are constantly online during all our waking hours?

Short-term use of a computer or mobile device is probably harmless to your vision, as an adult. However, there is evidence that the development of long-distance visual acuity when we are young may be hampered by too much close work. In some Asian countries, where school days can be quite long and there is a low emphasis on outside activities and sport, the rates of short-sightedness are climbing. In some schools in China, desks with restraining bars have been installed to prevent children from getting their heads too close to their books in an attempt to mitigate against this.

A less obvious and less well-appreciated consequence of these technologies, which is affecting adults and children, however, is the impact on the body clock. The LCD screens in many mobile devices and laptops issue very blue-dominated light. This strongly stimulates the cells in the back of the eye that are used to set the body clock, fooling the brain into thinking it's perpetually morning. This leads to disturbed sleep, which in turn can lead to poor learning, concentration and memory, over-eating and weight gain.

[evan_au]

The rationale for limiting refined sugar intake is that these simple sugars are absorbed very rapidly from the small intestine.

This then starves your microbiome, with potential side-effects that we are only now starting to glimpse.

Fiber in the diet provides a home for your microbiome, and they slowly break down foods into a form that can be readily absorbed, but without the spike in blood glucose.