Fleeting hunger games

A couple of months ago I set myself an ambitious goal: to find a way to live longer, stay younger and lose weight while enjoying the foods I normally eat.

I cannot seriously imagine living on a severely kilojoule-restricted diet for the rest of my life. Fortunately, there is an alternative , intermittent fasting, reducing your food intake on alternate days.

One of the links between fasting and longevity seems to be a hormone called insulin-like growth factor 1. IGF-1 and other growth factors keep our cells constantly active.

You need adequate levels of IGF-1 and other growth factors when you are growing, but high levels later in life appear to lead to accelerated ageing.

Fasting lowers the level of IGF-1 and appears to switch on DNA repair genes. The reason seems to be that when we run out of food our bodies change from "growth" to "repair" mode.

But fasting is not for the faint-hearted, and is done safest in a specialised centre or under other supervision. It causes a drop in blood pressure and glucose levels and metabolic reprogramming. Some people faint.

I started my trial fast on a Monday evening and finished it on the Friday. During that time I drank black tea, black coffee and lots of water, but consumed no food.

By Friday morning I had lost body fat, my blood glucose levels had fallen dramatically and my IGF-1 levels had halved. I improved my body chemistry and learned I could tolerate hunger better than I imagined. But to maintain these benefits I would have to change what I eat or try something else.

Dr Krista Varady of the University of Illinois at Chicago has been testing a new diet on volunteers. It's called Alternate Day Fasting, On fasting days you're allowed about 2500kJ a day if you're a man, or about 2100kJ if you're a woman.

On ''feed days" you can eat what you want. Volunteers reported weight loss and a drop in LDL cholesterol - "bad cholesterol" - and blood pressure.

I opted for a less dramatic variant of the ADF diet, the 5:2 diet. You eat what you want five days a week and twice a week you restrict yourself to 2500kJ .

There is no official guide to what a 2500kJ meal looks like and it doesn't seem to matter which days of the week you restrict your eating. I have kept it up for two months and, after a settling-in period, it has become quite easy.

Six weeks after starting the 5:2 diet my blood glucose, which had been borderline diabetic, was normal and my cholesterol levels, previously high enough to necessitate medication, were down in the healthy range. I look better and I feel good. I still sometimes eat burgers, biscuits and cake, but on my fasting days I eat healthily.

Intermittent fasting is not something many doctors recommend. So far there is limited evidence of its efficacy in long-term human trials. It will not suit everyone, nor is it safe for everyone.

It worked for me and I'll keep doing it. Or, I think I will. We'll see. - ©The Daily Telegraph

• Michael Mosley is a medical doctor, journalist and television presenter. To watch his BBC 'Two Horizon' programme on intermittent fasting, go to the BBC iPlayer (bbc.co.uk/iplayer) or visit tinyurl.com/BBCHorizonFasting. Before you try this diet speak to a health practitioner

THE 5:2 DIET:

ON FIVE days a week, the "feeding days", you can eat whatever you like. On the two ''fasting days" you eat 2100kJ if you're a woman, or 2500kJ if you're a man.

It doesn't matter which days are spent ''feeding" and which ''fasting", as long as the fasting days are not consecutive.

On fasting days, you can consume your kilojoules in one go, or spread them through the day.

A typical fasting-day breakfast of 1250kJ might consist of two scrambled eggs with ham (good sources of protein), plenty of water, green tea or black coffee.

For a typical 1250kJ lunch or dinner, try grilled fish or meat with vegetables.

On feeding days, you can eat whatever you like. Most dieters, rather than feeling a need to gorge, found that they were happy to consume about 8400kJ.

According to current medical opinion, the benefits of fasting are unproven. As a diet, it is not recommended for pregnant women, or diabetics on medication.

Anyone considering a diet that involves fasting is advised to consult their GP first.- Jennifer Smith