The Rogues Gallery

Fatuous and Foolhardy Fasting

We recently received an email from Michael C. about fasting:

I am a grad student in mechanical engineering at the University of Victoria in British Columbia. One of the people I share an office with is a PHD student from Germany. We often have discussions on a variety of issues you guys cover from week to week, and one day this led to the topic of fasting. My officemate claims that fasting is a worth while endeavor and he himself does it for health purposes. I went on webmd for some quick info on the practice and found the following claims/controversies about fasting.
1) That it can help with weight loss
2) That it can cleanse the body of “toxins”
3) It can cure certain diseases
4) You fast every night and are told to before surgery therefore
5) The ol’ people have been doing it for thousands of years so it must be good
6) It can help you live longer.

…

Thanks

Michael C.
Victoria, BC, Canada

Thanks for your questions Michael

Fasting is actually a good weight loss tool but only if you don’t care what kind of weight you lose. If you want to lose fat though then it’s not a good option. Much of the initial weight loss when fasting is water as it is with many drastic diets. This is why just using a scale is not the best way to track fat loss. I have found it helpful to use waist measurements in addition to a scale so I can better distinguish between fat loss and weight loss. A large initial loss of water from fasting may seem impressive but this weight will quickly return once you resume normal eating habits.

Fasting will eventually cause some fat loss but it can also cause you to lose muscle which is probably the second-worst thing you want to lose (the first of course is brain tissue). Muscle is among the most metabolically active tissues you own and losing it contributes to another major reason why fasting is bad for fat loss…it slows down your metabolism. This is the last thing you want to happen because now you’re actually burning calories more efficiently. It therefore takes fewer calories to maintain your weight. This makes sense from an evolutionary perspective. When mammoths were scarce, the body slowed things down to conserve energy. Once food became available again, weight would be gained rapidly to prepare for the next bout of extended hunger. This doesn’t sound like the best way to lose fat to me.

The bottom line with fasting and all diets for that matter is that they don’t work. The vast majority of people who diet regain the weight they lost. This has been shown in study after study. Permanent lifestyle changes that you can live with is the best way to go, not some temporary radical change. “Eat less and move more” should be your mantra, not “stop eating for a while”.

Next we have the whole removing toxins hubbub. We are to believe I guess that daily living with all its environmental poisons and toxic food additives causes a build-up of toxins in our bodies that need to be regularly cleaned out by fasting and probably a compromising colon cleansing There is however no biological basis to claim that fasting (or enemas for that matter) can cleanse your body of toxins.
Your body needs no help in this regard. Your liver, lungs, colon, kidneys, and skin do a fine job in the toxin removal department thank you very much. If you still feel the need to ream out your colon then hydrate properly and eat plenty of fiber instead of calling roto-rooter.

Next we have the claim that fasting can cure diseases. I wasn’t able to find any studies that showed a relationship between stopping eating and stopping any disease. This of course is not surprising since eating is kind of important for over-all health. Extreme fasting or near-starvation has been shown however to weaken your immune system even for something simple like a cold.

If you poke around this particular topic you may come across some studies that seem to show that fasting may help with some conditions like diabetes. In these experiments rats that fasted every other day and ate whatever they wanted on the other days were more resistant to diabetes and some other ills than the controls. Study author Mark Mattson PHD has hypothesized that each fast is like a bit of stress that causes the release of stress-resistance proteins. Other studies however have shown that calories consumed overall tend to go down with this type of fasting regimen and that is what explains this increased resistance.

Fasting isn’t of course anathema in all situations. Often surgery and other medical procedures require some fasting. If a “real” Dr tells you to fast before having a procedure, do it. When you’re having surgery and under anesthesia, digesting food is an extra unwanted variable. This is especially true for abdominal surgery. Puking would also be contraindicated at this time.

Some medical tests such as those for cholesterol or blood sugar would also not be accurate enough if you ate beforehand.

It is true that people have been fasting for thousands of years. To argue that this means the practice is good sure sounds like a logical fallacy to me. Probably something along the lines of an argument Ad Populi or more specifically the Argument from Antiquity. People have been doing all sorts of nasty things to themselves for thousands of years. That which doesn’t kill us isn’t necessarily helpful.

The last question about longevity I believe confuses fasting with calorie restriction. Permanently restricting calories to a minimum with sufficient nutrition has extended the lives of rats and yeast in experiments. This effect has not been shown in humans yet. Occasional fasting is a different thing and I don’t think that the Calorie Restriction effect could be induced if overall calorie consumption remains near normal.

I don’t think there’s much more to say about this topic except maybe…Fasting…..it does the body bad.