Is it possible to lose weight fast? - Hei Man Chan

In the wealthiest circles of Victorian England, bizarre fads ran rampant. But perhaps none was as strange as the tapeworm diet, in which dieters swallowed an unhatched tapeworm and let it grow inside them by consuming undigested meals. Obviously, this is an exceptionally dangerous and unhealthy way to manage your weight.

However, while modern fad diets aren't usually this extreme, they do promise similar results; specifically, losing weight fast. So, are there any fast diets that do work? And are any of them actually healthy for you?

To answer these questions, let’s consider a thought experiment. Sam and Felix are identical twins both planning to go on a diet. They share the same height, weight, fat and muscle mass.

But Sam is hoping to lose weight slowly, while Felix wants to go fast. Sam's plan is to gradually decrease his calorie intake and increase his regular exercise. With less energy coming in and more being expended, he’s creating an energy deficit inside his body.

To compensate, Sam’s body begins breaking down his emergency glucose supply, stored in the liver in the form of glycogen. Then, after 4 to 6 hours, his body starts burning fat cells as a major energy source. This process releases lipid droplets which are broken down into compounds that float through the bloodstream and provide energy to organs and tissues.

Felix aims to create a similar energy deficit by dramatically cutting his calorie intake. Unlike Sam, who’s still eating smaller meals, Felix is eating almost nothing. And his body responds by going into a starvation response.

Felix’s body breaks down his entire store of emergency glucose in just 18 hours. And while Sam steadily replenishes glycogen with every healthy meal, Felix’s low-calorie diet does not. Desperate for energy, his body starts breaking down other materials, including his muscles.

Meanwhile, Sam’s regular exercise is maintaining his muscle mass. This means he’ll use more energy both during exercise and at rest, making it easier for him to lose weight. Felix, on the other hand, is losing muscle mass and burning fewer calories than ever for his body's basic functions, making weight loss even more difficult.

Despite all this, there’s one element of Felix’s fast diet that might make him think he's on the right track. Every gram of glycogen is bound to several grams of water. This can add up to two kilograms of water weight, all of which is lost when the glycogen is depleted.

For Felix, this might seem like he’s losing weight fast. But as soon as he stops starving himself, his body will replenish its glycogen store and regain that weight. Clearly, Felix’s plan does more harm than good, but extreme calorie reduction diets aren’t the only regimens promising to shed weight fast.

Plans called “detoxification diets” either promote or restrict certain foods to provide specific nutrients in high quantities. These can be useful for addressing some nutritional problems, but they’re far too specific to be used as general cure-alls. For example, for a person with low vitamin A, a juice diet might be helpful.

But for someone high in vitamin A, juicing could be disastrous. And regardless of personal nutrition, maintaining a juice diet over multiple weeks is likely to compromise the immune system due to a lack of essential fats and proteins. Therein lies the problem with all these fast-moving diets— whether you’re cutting calories or food groups, extreme diets are a shock to your system.

There are well-established rates of healthy weight loss motivated by both diet and exercise that account for genetic and medical differences. And staying on those timelines requires a dietary lifestyle that’s sustainable. In fact, some of the worst side effects of extreme diets are rarely discussed since so few people stick with them, it also bears mentioning that many societies have unhealthy relationships with weight, and people are often pressured to diet for reasons other than health or happiness.

So rather than trying to lose weight fast, we should all be taking our time to figure out what the healthiest lifestyle is for ourselves.