For frustrated dieters, fasting for weight loss can seem like a tempting quick fix: melt off pounds without the bother of preparing complicated recipes or following a rigid meal regimen. But is it safe?
Most medical experts consider long-term fasting to be unhealthy, if not downright dangerous. The health effects can be severe. People with chronic diseases like diabetes are advised not to attempt fasting. But some new evidence suggests that a modified form of fasting (short-term with some low calorie intake) may not only jump-start weight loss, but also reset metabolism.
Fasting has been around for thousands of years and has been used by many sects. Early humans fasted by default when food was in short supply. Illness, stress and anxiety can affect appetite and lead to temporary fasting. Many religions incorporate fasting as part of rituals and observance. Whatever the reason for fasting, the human body reacts the same way: energy needs are met by burning stored fat and, in extreme cases, breaking down muscle tissue.
At first, weight loss may seem dramatic, as your body's glycogen stores are quickly used up. Glycogen is stored carbohydrate, and it's always stored with water. So as the glycogen is burned for fuel, that water is flushed out. This could amount to a few pounds of fluid loss, which looks good on the scale, but it isn't fat loss.
As you continue fasting, your body mobilizes fat tissue for energy needs. Muscle may also be broken down and turned to glucose, which is a key energy source for brain cells.
Prolonged fasting can be unhealthy. Even when you consume few calories, you still need a certain amount of vitamins and minerals every day. If you eat nothing for weeks, you will not be consuming those vitamins and minerals, and your metabolism will suffer. You also won't be consuming any protein, which is critical to maintain cells and muscles. As cells wear out, they can't be replaced or repaired without protein.
The Dietician Perspective
Some dietitians who work with weight loss clients say they aren't fans of fasting.
"I have never recommended it and do not personally fast," said Elizabeth Pape, RD, LD. Jessica Corwin agreed and said, "I do not recommend fasting at all, as I do not feel we learn anything from the experience."
On the contrary, Rosanne Rust, MS, RDN, said, "I would recommend intermittent fasting. For instance, during Lenten season I 'fast,' which means a day of two very small meals and a normal meal, and no in-between snacking. I do think taking a day off and lowering calorie intake simply by doing that (skip one meal or two mini meals and no snacks) can't hurt for weight maintenance, but I wouldn't recommend a fasting program as an intensive weight loss program."