02/28/2025
Great info from our expert in Nutrition coaching: Michal Ofer Lifestyle & Wellness
Protein Sparing Modified Fast
Recently, the protein-sparing modified fast has gained widespread popularity among dieters. This is attributable to the significant amount of weight that can be lost during a short period of time. While the protein-sparing modified fast (PSMF) can help reach short-term weight loss goals, it’s highly restrictive and very low in calories and must be used with caution to avoid risking nutritional deficiencies and weight regain.
The term “sparing protein” does not necessarily mean that protein is better than other macronutrients; it refers to the diet’s main goal, which is to maintain muscle mass while losing fat.
In addition, to spare protein means that the diet provides adequate levels of essential amino acids to not impair the body’s ability to rebuild muscles and connective tissue .
A “modified” fast refers to a diet that is modified from other fad diets. This type of nutritional plan goes beyond simple caloric restriction for weight loss; it focuses on the quality and timing of food intake instead.
What Is A PSMF
A protein-sparing modified fast is a high-protein calorie-restricted diet combining several nutritional approaches including intermittent fasting, low-glycemic eating, and ketogenic eating. The principles of PSMF are simple; calories are restricted so that your body uses mostly fats as fuel instead of burning muscle tissues, which can be used even when fasting or not eating enough calories from protein.
The protein-sparing modified fast allows just enough protein and carbohydrates to provide energy for normal daily activities but the rest should come from dietary fats and protein foods such as lean meat, poultry, eggs and seafood like fish.
This semi-starvation approach promotes rapid fat loss while maintaining lean muscle tissue through increased secretion of growth hormone (GH). Even though many people believe that GH makes one “bulky” or causes unwanted body fat increase, research proves otherwise. GH actually spares fat stores by accelerating gluconeogenesis, a procedure that turns non-carbohydrate food sources into glucose to meet the needs of thyroids and other endocrine glands. As it is impossible to avoid gluconeogenesis while following this diet, there will be no decrease in muscle mass.
To ensure safe and effective weight loss using protein-sparing modified fast, one should eat moderately every day and create 12-14 hour daily fasting periods.
Importantly, a longer-term protein-sparing modified fast should be implemented under professional guidance, especially for women and girls who want to lose additional body fat without experiencing related health disorders. The dieter is examined regularly to ensure that they lose only adipose (fat) tissue while preserving lean muscle mass and overall health.
Meat products are consumed with every meal as they have been shown to promote faster weight loss compared with other types of food. However, all cooked foods should be thoroughly chewed before swallowing them, as eating in this manner helps lymphatic glands remove fats from food more effectively during digestion.
When following a PSMF one can eat very adequate amounts (depending on individual size and weight) of lean protein while consuming significantly smaller portions of non-starchy vegetables like broccoli, cauliflower, lettuce, etc. Small amounts of berries can also be eaten as long as they fall within the carbohydrate limitations. Fat consumption is also limited.
Benefits Of A PSMF
Following a PSMF has been associated with several benefits, including:
WEIGHT LOSS
Research has proven that this weight loss protocol can have positive short-term results. The concept behind it is that by consuming only a very low amount of calories per day, patients will lose a significant amount of fat while keeping lean muscle mass untouched.
Compared to traditional low-calorie diets, a PSMF is easier to stick to because the dieter is allowed plenty of food options and can eat regularly throughout the day.
IMPROVED BLOOD SUGAR CONTROL
PSMF supports better blood sugar control, especially for people with diabetes. Although it’s a semi-starvation diet, its low glycemic index makes it safe to use for both types I and II diabetics.
PROMOTES HEALTHY THYROID LEVELS
Many people have been able to regulate their thyroid levels by following a protein sparing modified fasting protocol. High levels of thyroid hormones are linked to obesity, and regulating weight can, in turn, support healthy thyroid function.
MINIMIZES HUNGER PANGS
“Hunger pangs” is a term used for feelings of weakness and hunger that occur due to inadequate caloric consumption. As PSMF contains foods that are low on the glycemic index but incredibly nutrient dense which minimizes these feelings.
DECREASED CHOLESTEROL LEVELS
Research suggests that eating moderate amounts of protein, rather than high-carbohydrate foods, may significantly decrease total cholesterol levels.
Drawbacks Of A PSMF
As with any nutrition protocol, there are potential risks associated with following a protein-sparing modified fast diet plan.
One risk is that the low-calorie intake could lead to malnutrition. A person who chooses a PSMF should ensure adequate micronutrient intake, especially vitamins B and D. This is supported with optimal protein consumption.
Additionally, the diet could trigger disordered eating; however, this can be minimized by closely following healthy routines around food and exercise.
As with any diet, a PSMF might be difficult for some people to adhere to and the protocol may fail at helping weight loss in an acceptable amount of time. While there may be initial weight loss as water weight is lost, it may become unrealistic to lose large amounts of weight while still adhering to the diet.
A PSMF is not recommended for the following people:
· Older adults
· People with a history of disordered eating
· Pregnant or breastfeeding women
· People with a BMI lower than 27
Using PSMF With Keto/Carnivore
The Protein-Sparing Modified Fast is another tool that, if used correctly (and safely!) can help break a weight loss plateau or kick start your weight loss again.
· Use a PSMF macro calculator to get an estimate of how many grams protein per day to eat. The calculator will also tell you calories, grams of fat and carbs as well.
· Follow these macros for a MAXIMUM of 3 days per week. Preferably alternating days rather than consecutive days. Do not be tempted to think that if 3 days a week helps your weight loss along then more will be better. No, more will not be better and you will just be doing a crash diet, not making a permanent lifestyle change.
· Keep in mind that this is a temporary diet. Once you are past your weight loss stall and things are moving again, reduce the frequency of PSMF days.
PSMF Foods
Here are some of the foods you can eat as part of a PSMF:
· Poultry – skinless chicken, turkey, goose, and duck
· Meat – lean beef, pork, and lamb
· Seafood – any types of fish, but avoid shellfish
· Vegetables – almost all types (except for potatoes, corn, and carrots, and any starchy vegetables)
A protein-sparing modified fast limits carbs and fats.
Some foods you should avoid:
· Fruits – especially bananas, apples, pears, melons, and other fruits with lots of sugar
· Berries – especially strawberries in large quantities
· Grains – wheat, oats, barley, millet, quinoa, and buckwheat
· Legumes – black beans, lentils, kidney beans, peanuts, and chickpeas
· Processed foods and fast foods
· Artificial sweeteners and sweetened beverages
Final Thoughts
People who want to lose weight quickly while improving their overall health may find it helpful to follow the protein-sparing modified fast. It has been used for years by people seeking weight loss without losing muscle tissue or feeling hungry many hours a day.
Although many people find this semi-starvation approach to be highly restrictive and difficult to follow long-term, it can still be a safe and effective option for weight loss when performed under the guidance and supervision of a healthcare professional or as an added tool to include a few days a week on a low-carbohydrate protocol.
