Professor Roy Taylor gives us his final update, including thoughts on how we've changed as a species over the years and some parting hints and tips.

Tell us about the trouser test…

The trouser test is really important! We can describe how big people are in terms of BMI or waist measurements, but of course some people are naturally a bit bigger than others. So one acid test is whether a person can fit into the trousers they wore when they were 20.

Even though most people steadily gain weight throughout their life, that’s not inevitable - it’s just a feature of our developed society. So on a personal note, I’m pleased to be able to tell you that I can still fit into my student trousers!

Our species first emerged over 200,000 years ago and over almost the whole of that time, survival has depended on being able to find enough food, and also to store it within the body.

We have evolved lots of mechanisms for ensuring we can survive - but there have been no pressures to make the species develop mechanisms for dealing with excess food and little exercise.

So in the last 60 years, for the first time ever, the whole population in developed countries has been exposed to a fairly uniform excess of food. In the past, it was only the very few who were likely to be able to become obese, but now, suddenly and for the first time everybody in the developed world can do it.

For Dave and Si, how has this weight loss helped them physically?

Well, one thing it’s done is give them more energy! They have to carry around less weight of fat with them and they can move around much more easily. Their knees don’t have to do so much work and they’re more nimble. We know they feel better when they wake up in the morning because the quality of sleep improves so much.

These factors really make people feel much better everyday - the whole point of medicine is to make people feel better.

Looking into the future, Dave and Si will have decreased the risks of running into a stroke or a heart attack or the plethora of other problems associated with obesity, ranging from piles to cancer to diabetes. There are huge benefits in not being overweight.

Did the Bikers exceed your expectations?

They did extremely well. I gave them very clear targets and plotted a graph of what weight they should be at what time. At the end they lost more weight than I had set as a target - they exceeded my expectations.

What should you do when you’ve reached your target weight?

At the end of a deliberate period of weight loss it’s an excuse for a big cheer, but then you’ve got to dig in for the long term as its not good to get down to your ideal weight for just one day. You’ve got to stay at that weight for the rest of your life! In order to do this you have to adopt a different strategy:

- Weigh yourself weekly and write it down

- Party and pay back: you can go to parties and enjoy yourself but you need to cut back sharply over the next few days to prevent weight gain happening

- Walk, cycle and take the stairs: you must increase your daily physical activity.

Any final hints and tips?

People need to make an initial decision about making a big difference to their lives – do they want to lose a substantial amount of weight, or would they prefer to continue with their lifestyle?

If they’d like to change, they need to set themselves targets and decide when to start. If they already have diabetes they should discuss this with their doctor of course.

Then they need to be determined to succeed and if they are, they will.