Wednesday, March 20, 2013

Underlying Reasons for Weight Loss from The Fast Diet and Intermittent Fasting

I discussed research and my thoughts on intermittent fasting, such as The Fast Diet, two weeks ago. In the post, I pointed out two alternate-day fasting (ADF) studies resulted in weight loss for the fasting participants. The studies covered populations that ranged from a "healthy" weight to obese. While ADF features three to four fasted or semi-fasted days, The Fast Diet requires only two semi-fasted days per week (their semi-fast days consist of 500-600 calories consumed).

The line graph shows the percent of body weight loss during each day of a 22-day ADF study with healthy to overweight individuals. The bar graph shows the amount of fat and fat free weight, in kilograms, at the start and end of the study. The participants lost 3 lbs, with 1.8 being fat tissue.

How can The Fast Diet and other intermittent fasting programs provide weight loss? Here are two explanations:

  • We don't compensate for food deprivation periods. A three-week study at Cornell University examined intake following a fasted day [1]. The study participants spent Tuesday through Friday in a metabolic ward, eating as they please (a metabolic ward is a research-based section of a hospital that is not completely controlled, but fairly well monitored). Mondays rotated between eating as they please, eating a maximum of 1,200 calories, or fasting for the entire day. Every participant partook in all three scenarios. For Monday through Friday, all food was measured to determine total intake before and after meals. The researchers were interested to see if semi-fasted or completely fasted Mondays would lead to a greater intake over the rest of the week. As you can see in the graph below, despite the varying intakes on Mondays, the average daily intake from Tuesday through Friday of each week was no different.

  • Insulin levels change. Research shows that the rate of fat breakdown during a fast increases greatly after roughly 12 hours [2]. I believe insulin is a major underlying factor. As you may know, insulin is a hormone produced by your pancreas to taxi glucose from your blood to your liver and muscle cells. When insulin is abundant in your blood, your body is in an anabolic, or building, state. Therefore, if insulin is abundant, your fat stores will only increase. During a fast, blood insulin levels decrease because there is no major increase in blood glucose levels. Therefore, your body reaches a state favorable to tissue breakdown, specifically with your fat tissue.

In a nutshell, fasting or semi-starvation for one day each week likely won't trigger a full compensation over the rest of the week. With The Fast Diet, followers are experiencing two semi-starvation days per week. Unless they are taking extreme measures on other days (i.e. eating dessert or going out for dinner on all non-fasting days), it's very unlikely that followers will atone for the lack of food consumed on the fasting days. Also, long food droughts lead to lower levels of circulating insulin, allowing the body to enter a state favorable for fat breakdown.

These are not all of the underlying reasons, but just two ways to explain why intermittent fasting routines, such as The Fast Diet, are often successful in producing weight loss.

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