Intermittent Fasting Improves Insulin Sensitivity Even without Weight Loss

The modern paleolithic man feasts, famines & burns shopping carts. (Photo by Misserion)

Though you may not have heard the term that often, insulin resistance is a big health problem these days.

What insulin resistance means in practice is that normal amounts of insulin are not enough to produce an insulin response – a signal for cells to take up glucose from the blood. The result of prolonged insulin resistance is diabetes, and everyone has heard of diabetes.

Since diabetes is really the end result of a long process (which has the ultimate end result of death), it's much easier and more economic to tackle insulin resistance before things get out of hand.

Several small meals or a few big ones?

The traditional wisdom says that the key to staying healthy, lean and fit is to eat several small meals a day. "Keep blood sugar levels constant" and "breakfast is the most important meal of the day" are the mantras recited often by the ever-working slaves of the food pyramid. The same people are often quick to remind you that not eating at least six loaves of bread each day will surely kill you.

But there are also different, non-conventional approaches to this problem. One of them is intermittent fasting, which I have been following for the past six months (click here for the latest update). It's based on the idea that the paleolithic man didn't have access to food all the time. Instead, he would go for long periods without food (hunting and gathering), and when food was available (after a succesful kill), he would eat a lot. Feast and famine.

In short, the intermittent fasting approach is the complete opposite to common wisdom, which you've undoubtedly been taught ever since you were on an all-milk diet.

So who is right – your mother who warned you not to go too long without eating, or those crazy blogger folks who want you to get in touch with your inner caveman? When it comes to insulin sensitivity, whose cuisine reigns supreme?

Intermittent fasting and insulin sensitivity

Lucky for us, there are scientists out there working day and night to answer these questions. Among them are Halberg et al., who subscribe to the paleolithic feast and famine theory in their paper. They studied the effect of intermittent fasting on insulin action in eight young and healthy Caucasian men.

The participants were told to fast every second day for 20 hours. Each fasting period started at 10 PM and ended at 6 PM the following day. The study lasted for two weeks, giving a total of seven fasting periods. The subjects were told to eat as they normally would, except for two days before insulin measurements when they had to eat 250 grams of carbohydrates per day.

Body weight and body fat did not change during the experiment. Fasting (after an 8-hour overnight fast) plasma glucose and plasma insulin concentrations were also similar before and after the intermittent fasting experiment.

However, an increased insulin action on glucose uptake was noticed after the IF period. In other words, when the participants had gone through their two-week intermittent fasting experiment, their insulin was more effective in telling cells to take up glucose from blood. Increased inhibition of lipolysis, the breakdown of fat stored in fat cells, was also noticed.

Even though both of these – more glucose taken from blood and less breaking down of fat – may seem like negative things at first glance, they are important functions of insulin. An increase in these means improved insulin sensitivity. When insulin fails to do these things, that's when there's a problem.

After each 20-hour fasting period, the amount of circulating adiponectin was increased by 37% on average. Plasma adiponectin is positively correlated with insulin sensitivity, which explains the increased insulin action noticed after the IF period.

Conclusion

After two weeks of intermittent fasting, body weight, body fat percentage and muscle energy stores were unchanged in a group of eight healthy men. Insulin levels were unchanged, but insulin activity increased (a similar effect to that of green tea, black tea & oolong tea).

The fact that the participants lost no weight means that the improvement in insulin sensitivity is not due to a restriction in calories but the fasting periods themselves. This lends support to the idea that periodical fasting is beneficial for insulin sensitivity. Time to hear the inner caveman's call?

For more information on intermittent fasting and insulin, see these posts:

Intermittent Fasting with a Condensed Eating Window – Part I: Poorer Insulin Sensitivity and Glucose Tolerance?
A High-Protein Diet Is Better than a High-Carbohydrate Diet for Weight Loss
Intermittent Fasting: Understanding the Hunger Cycle
Green Tea Extract Increases Insulin Sensitivity & Fat Burning during Exercise