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18.10.2010


Lean mass recovers quicker after fasting than fat mass: animal study

It makes no difference for rats' lean and fat mass whether they eat nothing at all for a few days or follow a restricted diet for a longer period of time. Fasting makes the digestive organs shrink though, according to the Japanese study we wrote about yesterday. Today we'll look at what happens when you start to eat normally again after dieting or fasting.

The same Japanese researchers recently published the results of an experiment in which they let slimmed-down rats eat as much as they wanted for a period of 12 hours. The researchers examined the fat mass, lean mass and digestive organs of their subjects.

Just 12 hours of recovery was enough to restore the size of the liver and stomach to that of rats that had not lost weight, the researchers discovered. And after the recovery period the small intestine of the fasting group was the same size as that of the rats that had lost weight gradually.

The figure below shows the effect on bodyweight, and the weight of the muscles, fat mass and digestive organs.


Lean mass recovers quicker after fasting than fat mass: animal study

Lean mass recovers quicker after fasting than fat mass: animal study


Apparently organs recover weight lost very rapidly after fasting. Which would suggest that damage caused by fasting remains limited.

Of course, half a day recovery is not exactly a long period. But the Japanese refer in their article to a 1986 study in which researchers observed rats during a 6-day recovery period after fasting. [J. Nutr. 116: 2536-2546, 1986.]

The researchers used adult female rats in this study. Some of the rats started with a diet containing 40 percent of the amount they usually ate [restricted], and the rest were given nothing at all for a couple of days [starved]. When both groups had lost 23 percent of their bodyweight, the re-feeding phase started. And that's when things started to get interesting.


Lean mass recovers quicker after fasting than fat mass: animal study

Lean mass recovers quicker after fasting than fat mass: animal study


If humans react in the same way to fasting as the rats in these studies, then strength athletes would lose the same amount of fat in a short period of fasting as they would from a longer period on a restricted diet. The advantage to fasting for a short period is that the athletes can keep up a high calorie intake for longer, allowing them more time to build up lean mass. Damage to the digestive organs is limited, so that shouldn't be a problem.

During recovery after a longer period on a calorie-restricted diet, the body gives priority to building up the fat reserves, but after a fasting period it's the proteins that are attended to first. So once athletes start to eat normally again after a short fasting period, it looks like they'll start by building up more muscle protein.

Now that's what we call a win-win situation.

Source:
Obesity Research & Clinical Practice (2010) 4, e191e199.

More:
Crash diet damages digestive system, not muscles: animal study 17.10.2010