How to Lose Weight Fast: Three Surprising Research Findings

How to Lose Weight Fast: Three Surprising Research Findings

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Disclaimer: None of the information in this article constitutes medical advice, and is just the opinion of the writer(s). We recommend that patients follow their doctor’s guidance in regard to weight loss.

Obesity is an epidemic in the United States. According to Centers for Disease Control (CDC) data, 41.9% of adults in the U.S. are obese and an even higher percentage are overweight.

But is losing weight fast and keeping it off possible? Are there research-backed strategies for rapid weight loss? Do men and women respond to rapid weight loss differently? And is it possible to lose weight fast without exercise?

In this article we'll answer all of these questions and more, as we analyze clinical studies on weight loss to share three research-backed options for losing weight fast.

We'll discuss how much weight loss is possible and in what timeframe, explain how men and women respond differently to rapid weight loss, and explain if it's possible to lose weight fast without exercising.

How Much Weight Loss is Possible?

Rapid weight loss has been studied in clinical trials.

A clinical trial published in the International Journal of Endocrinology Metabolism compared a rapid weight loss program to a more gradual weight loss program.

Both groups were placed on a restricted-calorie diet, but the rapid weight loss group restricted calories to a greater degree. The rapid weight loss group was able to lose over 5% body weight in 5 weeks. 

A 2017 clinical trial demonstrated that participants lost around 10% of their body weight over the course of 46 days on an extremely low-calorie diet. The diet only allowed for 721 calories per day.

Clearly, it’s possible to lose weight fast with lifestyle interventions, and there may be no need for more extreme or riskier measures like surgery.

Most clinical trials on rapid weight loss that we came across while researching this article involved reducing calories, which is unsurprising as this is the most easily-modifiable lifestyle factor.

But in the next three sections of this article, we'll share some more unique, research-backed weight loss options for overweight individuals to speak with their doctor about.

Strategy #1 —Intermittent Fasting

As we outlined in our DoFasting reviews article, intermittent fasting is clinically shown to cause weight loss.

This doesn’t mean that it will be effective for everyone; just that it will cause weight loss for most people if applied properly.

Intermittent fasting involves fasting for extended periods of the day (typically 16 hours), and then consuming the day’s worth of calories in a restricted window (typically 8 hours).

A 2020 medical review on intermittent fasting for weight loss analyzed results from 27 clinical trials, and found that the participants lost weight in every single trial.

The methods of intermittent fasting used in the trials varied. Some groups performed 16-hour daily fasts, some groups performed alternate day fasts, while others significantly reduced caloric intake on alternating days.

The average weight loss documented in this review ranged from 0.8% of body weight in the least effective trial, to 13% of body weight in the most effective trial. The trial lengths ranged from 2 to 26 weeks. 

The group that lost 13% of body weight was on a program that involved three days of fasting and four days of unrestricted caloric intake per week. The fasting days allowed for 25% of typical caloric intake.

Strategy #2 — Paleo Diet

Different people have different optimal diets based on genetics and environment, but there's an interesting clinical trial regarding the Paleo Diet and rapid weight loss.

The trial examined weight loss in type 2 diabetic patients placed on a paleolithic (paleo) diet. This diet consists of foods that our hunter-gatherer ancestors would have consumed, and cuts out most agricultural products.

The trial participants were allowed to consume the following groups of foods: lean meat, fish, seafood, eggs, vegetables, fruits, berries and nuts.

The trial participants were disallowed from consuming the following groups of foods: cereals, dairy products, legumes, refined fats, refined sugars and added salt.

Fat mass decreased over 12 weeks by 12.57 pounds in the no-exercise group, and by 14.77 pounds in the exercise group.

A separate meta-study on the Paleo Diet concluded that the diet has favorable effects on weight loss and waist circumference.

Strategy #3 — HIIT

High-intensity interval training (HIIT) is a type of exercise that involves short bursts of intense exercise at nearly maximum capacity.

Some examples of this type of exercise would be hill sprints or biking on a stationary bike at maximum resistance. These bursts, or “intervals,” are broken up by longer periods of moderate or low intensity.

This form of exercise has been found to be extremely effective for fat loss in medical research, but it’s important to note that it may be unsafe for patients in poor physical condition.

We recommend that anyone considering HIIT to lose weight get this activity cleared by a doctor first, because it may not be safe for patients with high blood pressure or morbid obesity.

A 2019 medical review was titled “Is interval training the magic bullet for fat loss?” 

The researchers found that high-intensity interval training caused 28.5% greater reductions in absolute fat mass than similar workouts at moderate intensity.

Even though the calories burned may have been similar, HIIT appears to cause favorable metabolic changes that lead to greater fat loss over time.

One of the benefits of HIIT training over standard workouts is the time efficiency. It's possible to be in and out of the gym in 25 minutes or so, because the workouts are more intense and rests between sets are shorter.

Is Rapid Weight Loss Worse for Women?

Early research suggests that men and women may respond differently to rapid weight loss.

A clinical trial published in the Diabetes, Obesity and Metabolism journal analyzed results from 2,500 men and women on a restricted-calorie diet.

The study authors reported that men tolerated the rapid weight loss program better. Men experienced 16% greater weight loss, and greater reductions in markers of metabolic syndrome and heart rate.

Women had larger reductions in HDL (“healthy”) cholesterol levels, which isn’t necessarily a good sign.

The medical community hasn’t established why there could be a sex difference in the effects of rapid weight loss, but future research will hopefully emerge explaining (or contradicting) this data.

This research suggests that women may benefit from more gradual approaches to weight loss.

Is Rapid Weight Loss Doomed to Fail?

Most restricted-calorie diets fail in the long-term. It’s possible to cut weight for a few weeks or even a month based on sheer will power, but this often isn’t sustainable.

Medical research shows that around 80% of people who lose significant body fat through dieting regain the weight after 12 months.

Simply cutting calories while still eating an unhealthy diet will often result in cravings. It’s not an intelligent strategy if no dietary modifications are made.

The average American eats processed and packaged food for a decent percentage of their overall caloric intake, and trying to just eat smaller portions doesn’t work for most people.

The diet is too low in fiber and the caloric reduction becomes an hourly struggle to avoid temptation.

Since we’ve established that cutting calories on the Standard American Diet and trying to starve yourself is an ineffective way to lose weight over time, a more effective approach seems to be increasing intake of dietary fiber which reduces cravings.

A landmark medical study found that moderate caloric restriction (750 calories per day below baseline) combined with dietary fiber intake (a minimum of 20 grams per day) caused an average weight loss of 16.03 pounds over 6 months.

That’s a pace for 32 pounds per year of weight loss in overweight individuals simply by adding fiber to a moderately-restricted-calorie diet.

Fiber is effective for weight loss because it increases satiation (feeling of fullness), slows digestion and takes up space in the stomach.

The difference in fiber content is the reason it’s relatively easy to eat a whole pizza that’s 2,000 calories in one sitting, but much more challenging to eat 2,000 calories of beans and salad in one sitting.

Can I Lose Weight Fast Without Exercise?

While exercise is an important part of an overall healthy lifestyle, it’s not necessary to achieve long-term weight loss success. The study linked in the previous section on dietary fiber intake had no exercise requirement.

Participants only reduced calories by 750 per day and consumed a minimum of 20 grams (g) of fiber each day.

Exercise burns calories, but it can also increase hunger, so its effect on weight loss may not be as significant as dietary changes.

Based on the available research, we consider it possible to lose weight fast without exercise, although we would always recommend exercise for general health maintenance and wellbeing.

Our Clean Weight Loss Picks

There are food-based nutrients which have been shown in medical studies to be effective for weight loss.

Dietary fiber was shown in a medical review published in The Journal of Nutrition to cause 16 pounds of weight loss in 6 months when combined with moderate caloric restriction (750 calories per day below baseline).

MBG Organic Fiber Potency+ is our top fiber pick because it's certified organic, provides 7 g of fiber per serving and costs under $1.85 per serving at the time of updating this article.

MCT oil was shown in a meta-study to cause more than one pound of weight loss over 10 weeks. This equates to potential annualized weight loss of 6 pounds per year with less than one tablespoon's worth of MCT oil per day.

Performance Lab MCT Oil is our top MCT oil pick because it's certified organic.

Ginger intake "significantly decreased body weight" according to a 2019 meta-study on ginger and weight loss that analyzed data from 14 clinical trials.

Pique La Ginger is our top ginger product, because it's an organic tea in convenient crystallized form, and all that's needed is to pour the powder into a glass and add hot water.

All three of the products mentioned in this section are entirely free of additive ingredients that we consider to be unhealthy.

Can You Lose Water Weight Fast?

If the goal is to reduce water weight, a low-carb diet is a logical solution.

Carbohydrate intake increases glycogen storage, which consequently increases water storage in muscles, according to medical data.

Water weight can significantly influence overall weight, so switching from a high-carb diet to a low-carb diet can sometimes cause temporary weight loss of up to 10 pounds.

It’s important to note that this isn’t true fat loss, and will likely be reversed if carb intake is increased.

We recommend that people speak with their doctor before making major shifts in their diet to reduce water weight.

It’s not necessarily a healthy choice, especially if the shift is made rapidly without giving the body time to adjust, and losing fat should be the goal for overweight individuals; not losing water.

Can You Lose Weight on Metformin?

Overweight patients are often curious about the ability of Metformin, an anti-diabetic medication, to cause weight loss.

Metformin is only approved by the Food and Drug Administration (FDA) to treat type 2 diabetes, so using it for weight loss alone would be an off-label use.

Metformin was shown in a clinical trial to be effective as a standalone weight loss treatment for weight loss, so perhaps the FDA will approve it for weight loss in the future if more research validates these early results.

The above-linked trial found that metformin supplementation at a dose of 2,500 milligrams (mg) per day caused an average weight loss of 12.79 pounds over 6 months.

We published an article titled does Metformin cause weight loss for readers interested in exploring this topic further.

Stay up-to-date on our research reviews


It's possible to lose weight fast with lifestyle modifications.

Based on the research we surveyed, reducing caloric intake is more likely to be effective than dramatically increasing calories burned.

Very-low-calorie diets are effective for short-term weight loss, but have unimpressive results in regard to long-term, sustainable weight loss.

Intermittent fasting, paleo diet and HIIT are all research-backed options that individuals seeking rapid weight loss can discuss with their doctor. 

We consider dietary modifications like increasing fiber intake to be a more logical approach to long-term weight loss than simply cutting out calories while still eating an unhealthy diet.

Fiber has zero calories and takes up space in the stomach, which is why it's been associated with weight loss in a number of clinical trials.

It's possible to lose weight fast without exercise, but exercise provides a number of other health benefits beyond potential weight loss.

Men and women respond differently to rapid weight loss, and early results suggest that men may tolerate this approach better.