Many popular diet programs advocate a fast as part of the dieting routine. This fast may constitute the entirety of certain short-term or “weekend” diets, or it may be the first step of a longer diet plan. Whatever the case, fasting is usually reported as a way to detoxify the bloodstream and promote a healthier body free of impurities. While fasting is not necessarily harmful, it’s usually not as beneficial as these diets may lead you to believe. In some cases, fasting can even make weight loss even harder to obtain.

How Fasting Works

The principle behind fasting is simple: The dieter simply avoids eating for a certain period of time. During this time, the dieter is usually advised to drink certain beverages. This may be cabbage soup, specially formulated diet shakes or vegetable juice. Certain substances are often advocated during fasts for their ability to detoxify the body and purge it of impurities. For example, wheat grass and kale are common juicing ingredients, and green tea is often recommended for its purifying properties.

Despite its associations with weight loss, fasting actually has ancient roots that have little to do with beauty. Fasting has been part of religious observances for thousands of years. In fact, it served as a cornerstone of many religious ceremonies in multiple cultures throughout history. Most religious fasts prohibit the participants from eating at all, advocating the consumption of water alone. Others may prohibit all but a few very specific foods. At the end of the fasting period, many religions celebrate with a feast.

The religious appeal of fasting may have something to do with its current popularity as a diet jump-start. Fasting causes the body to enter the first stages of starvation mode, which leads to alterations in brain activity. People may feel light-headed or shaky. As this period passes, a feeling of euphoria can sometimes fall over the person fasting.

In religious ceremonies, this euphoric feeling may have been linked to various other spiritual practices. In terms of dieting, it can feel rewarding and even triumphant for the person doing the fasting. Of course, the euphoric feeling is short-lived, and the effects of a fast are easily reversed by resuming normal eating habits.

Why “Detox Diets” Don’t Work

While it’s true that some substances help to promote overall health and well-being in the consumer, there is no need for a specific “detoxification” diet. The body is designed to detoxify itself and purge itself of impurities. That is the dedicated function of organs like the kidney and liver.

Additionally, it’s often difficult to pin down precisely what impurities are being targeted by a specific diet or why the dieter would need a detoxification diet to begin with. In most cases, “detoxification” is a vague term meant to appeal to dieters without having any real or substantial meaning behind it. Even when there are specific impurities to remove from the dieter’s system, there is no reason why a juice fast would be any more effective at purging them than any other healthy, nutrient-rich diet would be.

At the end of a fast, a dieter may be more likely to feel extreme hunger and a desire to over-eat. The body has, after all, been deprived of ample calories for the duration of the fast. Any weight lost during the juice fast may be quickly gained back due to this over-eating impulse. In fact, the dieter may gain even more weight as the body strives to keep on additional pounds as defense against future famines.

Is Fasting Worth It?

In the majority of cases, juice fasts are harmless but ineffective. For some people, however, fasting can be extremely dangerous. You should never fast without a doctor’s approval if you are pregnant, nursing, taking medications or have any blood sugar problems. People with diabetes should be especially wary of fasting.

If you are in generally good health, a short fast should not hurt you as long as you’re getting enough fluids to stave off dehydration. If the fast will last more than a few days, you’ll want to ensure that you’re drinking enough calories to prevent your body systems from shutting down. Again, consulting with a physician is a good idea to prevent the possibility of serious medical concerns.

In most cases, a detox diet is not a good idea. The best way to lose weight is simply to begin eating a healthy diet that you can sustain for the rest of your life. Rather than viewing a diet as a temporary fix, you should consider it a lifestyle change. This will help you lose weight and keep it off indefinitely.

Nevertheless, people transitioning into a new healthy lifestyle may find some benefit in juice fasting. The extremely restrictive juice diet may make a more liberal but healthy whole-foods diet seem more appealing. If you’re transitioning from a diet of heavily processed fast food to one made up entirely of vegetables, whole grains and legumes, for example, a juice fast may help. It’s certainly not an end in itself, however, and it’s not a necessary component of any dietary change.