Is fasting safe and useful for weight loss?

The act of fasting—abstaining from food for a specific period of time—is gaining in popularity among some fitness enthusiasts and weight-loss dieters as a means to reign in calorie intake, but it certainly isn’t anything new. Despite the recent interest in the subject among authors (The Fast Diet, The Overnight Diet, The Warrior Diet, The Alternate Day Diet, etc.), fasting has been practiced around the world for ages. Hunger strikes, religious fasting periods and extreme “cleanses” designed to “purify” mind and body are all variations of fasting (and for the record, I don’t recommend extreme “cleanses” or long term fasting—they can be dangerous). One of the biggest reasons—but not the only reason—that folks are becoming increasingly interested in fasting, is for help with weight control and weight loss.

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Some fast days involved eating highly restricted calories, which might mean low-calorie foods like plain popcorn.

What’s “intermittent fasting”?

The concept of “intermittent fasting” appears in many permutations. Some popular methods include fasting for 24 hours every few days a week, alternate day fasting, or simply concentrating one’s food intake into a period of 6-8 hours every day (thereby fasting for the other 16 to 18 hours per day)—sometimes called time-restricted feeding. Fast days also don’t always mean consuming no food whatsoever—some fasting protocols call for a small meal on fast days (some specify a calorie range, such as 400-500 calories). However you want to define it, fasting is being looked at more intensely by research scientists and health experts for its potential to bring about some health benefits.

Is fasting safe?

It can be…and it may not be. There are some folks who simply should not be fasting at all: those who are pregnant/breastfeeding, those who are underweight, those who have diabetes or a history of eating disorders, children/teens, people who are ill, etc. So you see, it’s not for everyone. The Academy of Nutrition and Dietetics acknowledges that preliminary human studies indicate that intermittent fasting may reduce risk factors related to cancer, diabetes and heart disease, but that additional human studies are needed. As with all things that may impact your health and wellbeing, a discussion with your doctor is warranted before jumping into fasting.

Fasting and weight loss

The basic idea behind fasting for weight loss is that by not eating, one is automatically going to decrease one’s caloric intake. Seems obvious, right? So, instead of just decreasing one’s caloric intake throughout the day every day, such as you would when following a typical weight loss plan, instead you would simply eat normally one day, then not eat the next day (or fast for most of the day and eat lightly during the remaining hours). If weight loss is your goal, this might be a method that works for you. Here are a couple of points regarding intermittent fasting that I think are important:

One of the big benefits is psychological.

Not having to think about “being on a diet” every day presumably cuts down on feelings of deprivation that many feel when following a weight loss plan. Aside from giving yourself a break from diet-brain, both animal and human research shows that intermittent fasting provides similar results to a standard, continuous weight loss plan (in terms of decreased body mass, fat loss, fasting insulin levels, etc), though it may not be superior to a traditional weight loss diet in actual pounds lost.

Lots of folks seem inordinately worried about sending their bodies into “starvation mode.”

Do you think our bodies are not smart enough to be able to handle not eating for a little while? If our bodies reacted by “starving” every time we missed a meal how would we have ever survived as a species? The human body is remarkable! We have enough glycogen (the body’s storage form of glucose) to get us through roughly one day provided we aren’t exercising vigorously. After about 24 hours or so, the body does make adjustments to preserve energy and utilize stored fuel (read, fat), but as long as fasts aren’t lasting longer than that, the body isn’t going to go into “starvation mode.”