What is a cleanse?

There’s no specific definition of a cleanse, but Prest says it typically involves restricting your diet for a short time with the intent of detoxifying the body—either from natural byproducts like lactic acid or outside forces like mercury in seafood or pollutants.

Doing a cleanse could mean cutting out dairy or gluten for a month, going on a liquid diet or juicing for a week, or simply fasting. Even diets like Whole 30 or keto could be considered cleanses. (Colon cleanses are also a thing—but that’s a whole different story.)

But the Academy of Nutrition and Dietetics, the world’s largest organization of nutrition and dietetics practitioners, doesn’t recommend cleanses. That’s because the body already has its own highly effective process to get rid of toxins, mainly through the liver, kidneys, and digestive system. For example, the body can metabolize alcohol in as little as a day, depending on how many drinks someone consumed (and how strong they were.)

(No, you can’t really sweat out toxins.)

Most cleanses fall under the category of “fad diets,” which often cut out food groups, don’t provide adequate nutrition, and promote short-term changes that are difficult to maintain.

Many companies offering cleanses label their products as “research-backed.” But those findings can be manipulated to fit a narrative. For example, a “lemon water detox” has become somewhat of a staple for the cleanse-conscious. But one study, often cited as the basis for this cleanse, monitored less than a hundred participants for only 11 days.

Most of the positive changes were also observed among subjects on a similarly calorie-restricted diet without the same lemon juice mixture. Many studies are also done on animals, the results of which don’t easily transfer to humans.

So what are the actual short-term benefits of a cleanse?

Ring, however, doesn’t rule out cleanses.

“It is as much a mental reset for people, and maybe more so than it is an actual physical reset. It helps people feel a sense of starting over. It helps them detox themselves of bad habits,” she says. “I’ll encourage people to do them in a healthy way but also be aware that there are limits to how much can actually be done.”

But it’s tough to pinpoint what a cleanse does to your body in the short-term because so many variations exist.

Some cleanses are aimed at reducing inflammation—which can be caused by foods like dairy or gluten, especially among people with intolerances. An estimated 68 percent of the world’s population doesn’t absorb lactose efficiently, according to the National Institutes of Health, and up to 7 percent exhibit gluten sensitivity. But reactions could be so slight, you may not even be aware of them—which may explain why some people feel better after eliminating those foods.

Inflammation affects a whole slew of physical processes and may lead to arthritis, gastritis, and bronchitis, according to Ring. So cutting those foods out, even briefly, could help. Certain foods or supplements, like ginger, garlic, and omega-3 fatty acids, have also been linked to decreased inflammation.

If you eat more fiber, which is food for the gut microbiome, you could also experience short-term benefits to your bowel regularity and digestion.

(Your gut health can affect the rest of your body. Here’s why.)

A single meal can have an impact on somebody’s microbiome. So there are some fairly immediate effects that we can see in the body’s chemistry, biochemistry and pathophysiology.

But if somebody goes back to heavy drinking and eating fast food and indulging, those things will be erased immediately. You could also easily achieve these benefits without paying hundreds of dollars (plus shipping and handling) for a five-day bone broth cleanse.
At the end of the day, a doctor is the best person to oversee elimination diets and diagnose food sensitivities, and medical experts don’t recommend cutting out any food groups if you don’t have a sensitivity.

How about the benefits of intermittent fasting?

Intermittent fasting is another popular detoxification strategy, which often involves eating only during 8 or 12-hour windows. This can also prompt some short-term changes in the body.

Most notably, not feeding the body induces a process known as autophagy, where cells essentially clean out their old and damaged components. The body is already constantly undergoing autophagy, but fasting can trick the body into doing it more. That’s not necessarily good.

(Can fasting help you live longer? Here’s what the science says.)

Autophagy certainly has a housekeeping role and if you increase it, you could probably have better housekeeping. But what we don’t know is where the line gets crossed between good housekeeping and now starting to throw out all your best china.

Emerging research shows that autophagy could be used to treat diabetes and fight off cancerous cells. However it’s not clear if inducing autophagy through fasting has the same benefits, and more research needs to be done on more people over longer periods of time.

Intermittent fasting can also help someone reach a state of ketosis more quickly, where the body burns fat for energy instead of glucose in the blood. It’s the ultimate goal of the keto diet, which includes high amounts of fats, moderate protein, and little to no carbs or sugar.

The jury is still out on the safety and long-term benefits of the keto diet, but a 2022 narrative review in the journal Nutrients linked ketosis to improved cognition in participants with Alzheimers. That ketotic state is associated with a sense of almost brain clarity and increased energy. It’s part of why people really can feel good once we do these ketogenic diets. For others, however, a side effect of the keto diet can be brain fog.

The dangers of cleanses

In rare circumstances, cleanses can have extreme and even life-threatening effects. For example, eating too many carrots or other foods with high levels of vitamin A can cause headaches and weakened bones. Excessive leafy greens, which are high in oxalates, can also damage the kidneys.

Other cleanses, especially those with extreme calorie restriction, could have the opposite effect as intended.

“The body loves to make sure that it can continue functioning, so it does all sorts of things to stay in survival,” Prest said. “It will slow the metabolism rate down, so that it can conserve the energy that it gets.”

So when you return to your typical calorie or nutrient levels after a cleanse, you might actually gain weight.

“With that slower metabolic rate, whatever is leftover may then get converted to fat or be stored and used again at a later time.

People may also go on and off different cleanses or diets. Those extreme fluctuations can be harmful to the body.
In people with diabetes, you can actually see differences in the DNA of those who dabbled with extreme diets and those who maintained healthier eating. It’s the extremes, going from one to the other, that potentially could also be injurious—just some food for thought for the next time you’re considering a reset.
Instead, doctors and nutritionists give the usual advice: Stay hydrated and eat enough fruits, vegetables, and fibre, regularly—not just for a few weeks in January.
That’s always going to be my preference: to make a longer-term and sustainable change.