Protein-Sparing Modified Fast Review: Does It Aid Weight Loss?

The protein-sparing modified fast diet was originally designed by physicians to help their patients lose weight quickly.

However, within the last few decades, it has gained widespread popularity among dieters looking for a quick and easy way to drop extra pounds.

Although the plan is often praised for its effectiveness, its safety and sustainability have been called into question.

This article takes a closer look at the protein-sparing modified fast and whether it’s effective for weight loss.

What is the protein-sparing modified fast?

The protein-sparing modified fast (PSMF) is a very-low-calorie diet designed to aid weight loss and preserve muscle mass.

It severely restricts calorie consumption while increasing the intake of protein-rich foods.

Additionally, the intake of carbohydrates and fats is very limited on this diet.

The PSMF was first introduced in the 1970s to help people with obesity lose weight under the guidance of a physician.

However, over the past few years, the diet has undergone several modifications. It’s also often followed without medical supervision, which can be dangerous.

How to do a protein-sparing modified fast

The diet is divided into two main phases: the intensive phase and the refeeding phase.

The intensive phase can last up to 6 months and involves limiting calorie intake to less than 800 calories per day.

To follow the PSMF, you must consume approximately 0.7 grams of protein per pound (1.5 grams per kg) of body weight. Generally, this should come from protein-rich foods like poultry, fish, eggs, low-fat cheese, and tofu.

Added fats like oils or salad dressings are off-limits, and carbs are restricted to around 20 grams or less per day.

During the refeeding phase, carbs and fats are slowly added back into the diet, and daily protein intake is gradually reduced by 7–14 grams per month.

Does it work for weight loss?

Studies show that a PSMF can be effective for rapid weight loss when performed under proper medical supervision. This is because the diet is extremely low in calories and high in protein, which promotes weight loss.

One small study in 12 adolescents on a PSMF found that participants lost an average of 25 pounds (11 kg) over a 6-month period. This accounted for about 10% of their total body weight

Another older, 6-week study in 15 people showed that following a PSMF reduced body fat by 32 pounds (14 kg) without significantly altering muscle mass

Potential downsides

Following a PSMF may be a safe and effective option for weight loss when performed under the guidance and supervision of a healthcare professional.

However, the diet is highly restrictive, very low in calories, and eliminates many important nutrients. This can increase your risk of nutritional deficiencies if you’re not being closely monitored.

A PSMF is not suitable for older adults, those with a history of disordered eating, women who are pregnant or breastfeeding, or those with a body mass index lower than 27

The bottom line

A protein-sparing modified fast is a highly restrictive diet designed to promote rapid weight loss by increasing protein intake and limiting your consumption of calories, carbs, and fat.

Some studies have found it effective for short-term weight loss and improvements in blood sugar control, cholesterol, and blood pressure.

However, it may also increase your risk of nutritional deficiencies and weight regain in the long run.