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How to Lose Weight Fast: A Research-Based Analysis

How to Lose Weight Fast: A Research-Based Analysis

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Read our Editorial Guidelines to learn more about what makes our site the premier resource for online health information.

Read our Editorial Guidelines to learn more about what makes our site the premier resource for online health information.

Disclaimer: None of the information in this article constitutes medical advice. This article is the opinion of the writer(s), and is presented for informational purposes only. 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, 42.4% of adults in the U.S. are obese and an even higher percentage are overweight.

Given these numbers, many people are curious if there are research-backed strategies for losing weight fast. Gradual weight loss over time is typically considered more sustainable, but more rapid weight loss is possible over short periods. It tends to come with more risks.

In this article we’ll analyze published medical research and explain several strategies to lose weight fast that have medical proof.

Is Losing Weight Fast Possible?

Before examining individual strategies, it’s useful to see if it’s even possible to lose weight fast without medical intervention, and if so what degree of rapid weight loss is possible naturally.

A clinical trial published in the International Journal of Endocrinology Metabolism compared rapid weight loss to slow weight loss. The rapid weight loss group was able to lose over 5% of their body weight in 5 weeks. 

The average weight at baseline in the rapid weight loss group was 85.5 kilograms (kg), which is equivalent to 188.5 pounds (lb). The average weight at the end of the trial was 80.3 kg, or 177 lb. This equates to a 6% weight loss in 5 weeks.

A separate weight loss trial from 2017 demonstrated that 10 women could lose around 10% of their body weight on average over the course of 46 days. The women were placed on an extremely low-calorie diet.

Clearly it’s possible to lose a significant amount of weight in a short period of time without requiring surgery or extreme measures.

Weight Loss Strategy #1: Intermittent Fasting

As we outlined in our DoFasting reviews article, intermittent fasting is proven to cause weight loss on average. 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).

Intermittent fasting is effective because it has favorable effects on metabolism.

An extensive medical review was published in 2020 examining whether intermittent fasting is effective for weight loss. The study authors analyzed results from 27 individual medical trials on intermittent fasting and weight loss, and found that the participants lost weight on average in every single trial.

This is an incredible result, especially considering that the actual 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 alternate days without totally fasting.

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.

Clearly intermittent fasting can cause patients to lose weight fast.

Weight Loss Strategy #2: Paleo Diet

We don’t generally recommend any specific diet model for overall health, but there is an interesting clinical trial involving the paleo diet and rapid weight loss.

The trial examined weight loss outcomes for 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 5.7 kg (12.57 lb) even without adding exercise, and by 6.7 kg (14.77 lb) in the paleo group also engaging in exercise.

A separate meta-study which reviewed many different clinical trials on the paleo diet concluded that the diet has favorable effects on weight loss and waist circumference.

The Paleo Diet appears to be an effective approach for losing weight fast, especially for people starting from an unhealthy Standard American Diet (SAD) high in processed food.

Weight Loss Strategy #3: High-Intensity Interval Training

High-intensity interval training (HIIT) is a type of exercise that involves short bursts of work at nearly maximum capacity. It could include 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 riskier for patients in poor physical condition than moderate exercise. We recommend that anyone considering high-intensity interval training to lose weight get this activity cleared by a doctor first, because it may not be safe for patients with high blood pressure or significant obesity.

A medical review was published in 2019 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 it’s more time-efficient. You can be in and out of the gym in 25 minutes or so, because the workouts are more intense.

Men and Women Respond Differently to Rapid Weight Loss

One fact that many people aren’t aware of is that men and women respond differently to rapid weight loss from a physical perspective.

A medical study published in the Diabetes, Obesity and Metabolism journal analyzed results from 2,500 men and women on a restricted-calorie diet. They found that men tolerated the rapid weight loss approach better. Men had 16% greater weight loss on average, 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 would be a sex difference in rapid weight loss outcomes, but future research will hopefully emerge explaining (or counteracting) this data.

This early data suggests that men may be more likely to see favorable results from short-term “extreme” dieting (which we wouldn’t recommend for health reasons).

Why Rapid Weight Loss Doesn’t Work Long-Term

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 will 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.

More Sustainable Alternative

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, the more effective approach is adding a significant amount 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 7.27 kg (16.03 lb) over 6 months. That’s a pace of 32 pounds per year of weight loss in overweight individuals simply by adding fiber to a slightly restricted-calorie diet.

Fiber can be obtained through the diet from foods like cooked beans and starchy vegetables like sweet potatoes. You can also use a fiber supplement like psyllium husk fiber for a convenient powdered solution.

If you choose to use a supplement, we recommend searching for a product without additive ingredients like added sugars or flavoring.

Fiber is so effective for weight loss because it increases satiation (feeling of fullness), slows digestion and takes up space in the stomach. Differences 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 steak, 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 successful long-term weight loss. The study linked in the previous section on dietary fiber intake had no exercise requirement.

Participants only reduced calories by 750 per day and ate a minimum of 20 g of fiber per day.

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

How to 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 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 always the healthiest decision, 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?

People often ask us about the ability of Metformin, an anti-diabetic medication, to cause weight loss.

Metformin is only approved by the Food and Drug Administration (FDA) in the U.S. to treat type-2 diabetes, so using it for weight loss alone would be an off-label use that we wouldn’t recommend.

Metformin has been proven 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 after more research confirms these findings. The study found that metformin supplementation at a dose of 2,500 milligrams (mg) per day caused an average of 5.8 kg (12.79 lb) of weight loss over 6 months.

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There exist research-backed methods of rapid weight loss. Intermittent fasting, paleolithic dieting and high-intensity interval training have all been shown in medical studies to cause significant weight loss in relatively short durations of time.

These methods typically involve more risk to patients in poor health, so we recommend that anyone considering these rapid weight loss methods get a doctor’s clearance first.

Significantly increasing dietary fiber intake over 20 grams per day is the most sustainable long-term weight loss strategy in our opinion, and the one we typically recommend.

Fiber makes you feel full faster, which allows for increased adherence to diet with reduced discomfort like cravings.

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