Those who exercise should take their activity level into consideration before making any dietary changes, especially when it comes to cutting calories. "Think about your physical lifestyle," begins Centeno. "Are you doing an intense cycling class most days? Are you more of the active type who gets exercise by running from meeting to meeting each day? Or are you more of the slow burn where a good yoga class once a week does it for you? It’s important to take into account activity level because most cleanse or reset days are lower in calories. If you are more active, you’ll likely need to supplement with a few whole-food snacks."

In fact, juice that's primarily fruit can cause blood sugar spikes and drops on par with eating a chocolate bar. "There are also no fibers in juice, which means it hits your bloodstream right away," Young continues. "Too much fruit can lead to too much sugar, and this can pose reverse effects."

The Right Way To Cleanse.

Detox diets: Do they work? - Mayo Clinic

“There is no science to suggest that you need to detox your body," Blake said. "Your body is smarter than that. You have built in detox organs, the liver and kidney clean up any waste that needs to leave the body."

What is a juice cleanse?

Do Juice Cleanses Work? 10 Truths About The Fad | HuffPost

But while detox programs have gained traction over the past few years, the idea of an internal reset is nothing new. "The general concept of body detoxification is thousands of years old," explains Golan Raz, head of global health division at Lycored. "Our body absorbs substances from the food we eat, the oxygen we breathe, and the environment we live in. While part of the substances the body absorbs are supportive to our physical wellness, others are not as much. A portion of those substances have the potential to be toxic to our physical system."

Overall, I'd rate the two-day cleanse as a 5 out of 10 in terms of required willpower, keeping in mind that my usual diet is fairly healthy-ish, and lost a total of 3.25lbs throughout the process (most of which reappeared after a few days of eating normal-sized portions). I liked the challenge of the experience and can't rate the taste factor of PRESS London's offerings highly enough, but I think if I were to do another cleanse in future that I'd prefer one of their offerings which include soup, to try and stave off some of those intense food cravings.