Fasting diets: 5:2 or 5 days a month?
There is a new fasting regime being promoted from that centre of health excellence, Los Angeles (
) involving a 5 day fast every month. It is supposed to prolong life (hence its brand name, ProLon) but there is little direct evidence.
An article in New Scientist this week examines the claims, and gives some research background. Interesting that:
“Another effect of fasting is that the body starts to run out of glucose in the blood and glycogen stores in the liver, which causes a metabolic switch: the liver starts converting fats into ketone bodies for the muscles and brain to use as fuel, a process called ketosis. This is why fasting almost always causes weight loss of somewhere between 2.5 and 8 per cent. But how long you need to fast before the switch to ketosis occurs is unknown. Longo says that it takes at least three days and that shorter fasts, such as the 5:2 diet, don’t last long enough to make it happen.
Mark Mattson at Johns Hopkins University in Baltimore, Maryland, who studies the effects of fasting on the brain, disagrees. “The liver holds maybe 700 calories-worth of glycogen and people’s general daily activity around the house burns maybe 70 calories an hour,” he says. If you’re not eating during that time, “you do the math, it’s around 10 hours”.
Add exercise into the equation and the switch can happen even faster, says Mattson. A vigorous run can burn 100 calories in 10 minutes. Get your sports shoes on a few hours after your last meal and it won’t take long to hit ketosis, he says…”
I reckon that I feel ketosis when I have been fasting for a bit and I am confronted with exercise: I get a slightly depressed feeling, like I don’t want to be energetic. Recognising that feeling for me means: now is the time to get “stuck in” and exercise even harder, because the fat will be burned!